.rs
.\" Troff code generated by TPS Convert from ITU Original Files
.\"                 Not Copyright ( c) 1991 
.\"
.\" Assumes tbl, eqn, MS macros, and lots of luck.
.TA 1c 2c 3c 4c 5c 6c 7c 8c
.ds CH
.ds CF
.EQ
delim @@
.EN
.nr LL 40.5P
.nr ll 40.5P
.nr HM 3P
.nr FM 6P
.nr PO 4P
.nr PD 9p
.po 4P

.rs
\v | 5i'
.sp 1P
.ce 1000
\v'12P'
\s12PART\ I
\v'4P'
.RT
.ce 0
.sp 1P
.LP
\fB
.EF '%	 \ \ \ ^''
.OF ''' \ \ \ ^	%'
.sp 1P
.ce 1000
\fBSeries R Recommendations\fR \v'2P'
.ce 0
.sp 1P
.ce 1000
\fBTELEGRAPH\ TRANSMISSION\fR 
.ce 0
.sp 1P
.LP
.rs
.sp 28P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.LP
MONTAGE:\fR PAGE 2 = PAGE BLANCHE
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 1
.ce 0
.sp 1P
.ce 1000
\fBTELEGRAPH\ DISTORTION\fR \v'2P'
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ R.2\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBELEMENT\ ERROR\ RATE\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.2''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.2	%'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964)\fR \v'6p'
.sp 9p
.RT
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that in practice, the error rate on transitions is not used and, with the 
development of data transmission, it is the notion of 
element error rate that has come into use,
.PP
(b) 
that in general, the expression \fIelement error rate\fR is
used with the meaning of \fIerror rate on unit elements\fR . Although this
equivalence of meaning is acceptable for isochronous signal trains, this 
is not so for start\(hystop signal trains. In fact, there may be elements 
in start\(hystop signal trains whose duration is different from that of 
the unit elements (for example, the stop element of a start\(hystop signal 
in accordance with 
International Telegraph Alphabet\ No.\ 2),
.sp 1P
.LP
\fIunanimously declares the view\fR 
.sp 9p
.RT
.PP
(1)
that the following definitions be adopted:
.PP
\fBelement error rate\fR : the ratio of the number of incorrectly
received elements to the number of emitted elements.
.PP
\fBunit element error rate for isochronous modulation\fR : the ratio of
the number of incorrectly received elements to the number of emitted
elements.
.RT
.PP
(2)
that, for start\(hystop signal trains, the notion of
character error rate be used;
.PP
(3)
that, when error rates are measured to assess the quality of a communication, 
the original message acting as a reference for the 
calculation of the error rate shall be considered as being free of error;
.PP
(4)
that measurement of the element error rate assumes that it has
been possible to record the elements received in such a way that they can be
recognized as being correctly or incorrectly recorded. As the result of an
error rate measurement thus depends on the recording system at the end 
of the connection, this system must be specified when the results of the 
element error rate are given. Whenever possible the element error rate 
should be measured at the output of the regenerating device which normally 
precedes the translation device; the signals should be translated for checking 
purposes. 
.bp
.sp 2P
.LP
\fBRecommendation\ R.4\fR 
.RT
.sp 2P
.ce 1000
\fBMETHODS\ FOR\ THE\ SEPARATE\ MEASUREMENTS\ OF\ THE\ DEGREES\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.4''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.4	%'
.ce 0
.sp 1P
.ce 1000
\fBOF\ VARIOUS\ TYPES\ OF\ \fR \fBTELEGRAPH\ DISTORTION\fR 
.ce 0
.sp 1P
.ce 1000
\fI(New Delhi, 1960; amended at Geneva, 1980)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.PP
For separate measurements of the degrees of characteristic
distortion, bias distortion and fortuitous distortion affecting a telegraph
modulation or restitution, the following is recommended where circuits and
voice\(hyfrequency telegraph (VFT) channels are used to carry information
employing International Telegraph Alphabet No.\ 2, without regeneration;
.sp 1P
.RT
.PP
\fB1\fR 
Measure the degree of overall distortion (at the actual mean
modulation rate) on text, for instance the \fBQKS\fR \ text specified in
Recommendation\ R.51 | fIbis\fR . Let \(*D be the measurement obtained.
.sp 9p
.RT
.PP
\fB2\fR Measure the degree of distortion on reversals at the modulation   rate
used in the measurement of \(sc\ (1) above. Let \(*D\d1\ube the measurement 
obtained. \(*D\d1\uis the sum of the bias and fortuitous distortions. 
.sp 9p
.RT
.PP
\fB3\fR 
By using a compensator fitted to the distortion\(hymeasuring
equipment,
for example a compensating winding on the distortion meter relay, reduce the
degree of distortion reading obtained to its minimum value. Let this figure
be\ \(*d. For practical purposes \(*d is the fortuitous distortion. \(*D\d1\u\ 
\(em\ \(*d\ is, for practical purposes, the bias distortion. 
.sp 9p
.RT
.PP
\fB4\fR 
Keep the distortion meter adjusted as for the measurement of \(*d. Measure 
the degree of distortion at the actual mean modulation rate on text 
(\fBQKS\fR text, for instance). Let \(*D` be the reading. \(*D`\ \(em\ \(*d\ 
is, for practical 
purposes, the characteristic distortion.
.sp 9p
.RT
.PP
\fINote\ 1\fR \ \(em\ This method gives approximate results; it is possible
that the equation \(*D\d1\u\ +\ \(*D`\ \(em\ \(*d\ =\ \(*D may not be exactly 
satisfied. 
.PP
\fINote\ 2\fR \ \(em\ The method can be applied by using either an isochronous
distortion\(hymeasuring set or a start\(hystop distortion\(hymeasuring set.
.PP
\fINote\ 3\fR \ \(em\ The fact that the separate measurement of degrees of
different types of distortion is said to be possible and that a method is
recommended for such a measurement does not mean that separate measurements 
of the degrees of different types of distortion are to be recommended when 
international routine maintenance measurements are carried out.
.RT
.sp 2P
.LP
\fBRecommendation\ R.5\fR 
.RT
.sp 2P
.ce 1000
\fBOBSERVATION\ CONDITIONS\ RECOMMENDED\ FOR\ \fR \fBROUTINE\ DISTORTION\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.5''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.5	%'
.ce 0
.sp 1P
.ce 1000
\fBMEASUREMENTS\ ON\ INTERNATIONAL\ TELEGRAPH\ CIRCUITS\fR 
.ce 0
.sp 1P
.ce 1000
\fI(New Delhi, 1960; amended at Geneva, 1964, Mar del Plata, 1968, and\fR 
\fIGeneva, 1980)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
Recommendations\ R.51, R.51 | fIbis\fR , R.54 and R.55;
.PP
(b)
that, for the measurement of the degree of distortion of signals on an 
international telegraph circuit, it is necessary to specify the best condition 
of observation in order to be sure that the measurement obtained gives 
a good indication of what the performance of the circuit will be during 
periods of normal traffic; 
.PP
(c)
that the observation conditions should be such that
their duration or their complexity does not unduly increase the load on the
maintenance services;
.PP
(d)
that certain Administrations, to determine these
conditions, have carried out statistical measurements of the degree of
individual start\(hystop distortion using distortion analyzers, the results of
which seem to be in agreement;
.bp
.sp 1P
.LP
\fIunanimously declares the view\fR 
.sp 9p
.RT
.PP
(1)
that the tests should be carried out at nominal modulation rates of 50, 
75, 100 and 200\ bauds, depending on the type of circuits 
concerned;
.PP
(2)
that the text transmitted during measurements should be
that of Recommendation\ R.51 | fIbis\fR ;
.PP
(3)
that the degree of transmitter distortion of text signals should not exceed\ 
1%; 
.PP
(4)
that, during normal maintenance tests, the duration of the observation 
should correspond to the examination of at least 800\ significant 
instants, whatever the type of distortion meter used, isochronous or
start\(hystop. At a modulation rate of 50\ bauds this results in an observation
period of about 30\ seconds. At other modulation rates, the observation 
should last about 20\ seconds; 
.PP
\fINote\fR \ \(em\ The period of observation required to assess properly 
the performance of tandem 
code\(hyindependent\ time\(hydivision multiplexers
may be much longer than for voice\(hyfrequency telegraph equipment.
.PP
(5)
that, when making start\(hystop measurements using test
equipment
that does not register the peak early and peak late reading simultaneously, 
the observation period should be divided into two more or less equal parts: 
one 
part during which the significant instants in advance of their theoretical
position could be observed and the other part during which the significant
instants coming later than their theoretical position could be observed.
\v'6p'
.sp 2P
.LP
\fBRecommendation\ R.9\fR 
.RT
.sp 2P
.ce 1000
\fBHOW\ THE\ LAWS\ GOVERNING\ \fR \fBDISTRIBUTION\ OF\ DISTORTION\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.9''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.9	%'
.ce 0
.sp 1P
.ce 1000
\fBSHOULD\ BE\ ARRIVED\ AT\fR 
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that for the sake of comparative studies of degrees of distortion, it would 
be well if the procedures for measurement of distortion, and the layout 
of results, could be standardized. The distortion in question 
is:
.LP
	\(em
	start\(hystop individual;
.LP
	\(em
	isochronous individual;
.LP
	\(em
	degree of start\(hystop distortion,
.PP
(b)
that the degree of isochronous distortion is of no
great practical interest, since it is the individual isochronous distortion
that, when isochronous distortion is present, supplies all the useful
information. Hence it is not proposed to include the degree of isochronous
distortion in this Recommendation.
.LP
\fIunanimously declares the following view\fR :
.sp 1P
.RT
.sp 2P
.LP
\fB1\fR 	\fBStart\(hystop individual distortion\fR 
.sp 1P
.RT
.PP
1.1
As regards start\(hystop individual distortion, the distribution
curves will be plotted by means of a statistical distortion analyzer. The
width of the measurement steps should make it possible to take measurements
with steps of 1%, 2%, 4%,\ 8%. A measurement will cover about 20 | 00\ 
transitions (measurement duration of about 15\ minutes at 50\ bauds: three 
transitions on the average per start\(hystop alphabetic signal). 
.sp 9p
.RT
.PP
1.2
The results will be shown on the graphs on the linear scale with
distributional representation, or on the normal probability scale with
cumulative representation, the ordinates being the probabilities or probability 
density and the abscissae the degree of distortion. 
.PP
1.3
For individual distortion, the curves will give negative (early)
and positive (late) distortion.
.PP
1.4
For more detailed studies, the number of transitions to be
examined may be higher than 20 | 00, the number depending on the chosen
probability that the nominal figure will be exceeded.
.bp
.sp 2P
.LP
\fB2\fR 	\fBIsochronous individual distortion\fR 
.sp 1P
.RT
.PP
2.1
There is the difficulty of synchronism between the transmitter
and the distortion analyzer, when the measurements are made at two different
points; moreover, the average propagation time of the signals is to be taken
into consideration when loop measurements are made.
.sp 9p
.RT
.PP
2.2
The methods of measuring and presenting the results will be the
same as for the preceeding case, but the transmitter and the analyzer will 
have to be synchronized as accurately as possible, taking into account 
the 
distortion values to be measured.
.sp 2P
.LP
\fB3\fR 	\fBStart\(hystop distortion\fR 
.sp 1P
.RT
.PP
3.1
This is a matter of the (maximum) degree noted during a
measurement. It is then necessary to decide on the length of the sample 
to be measured; the text to be measured will be composed at random. The 
measurement at 50\ bauds will last 30\ seconds, distributed as specified 
in \(sc\ 5 of 
Recommendation\ R.5.
.sp 9p
.RT
.PP
3.2
Distribution curves of these degrees of start\(hystop distortion
will be drawn as a function of the number of samples.
.sp 2P
.LP
\fBRecommendation\ R.11\fR 
.RT
.sp 2P
.ce 1000
\fBCALCULATION\ OF\ THE\ \fR \fBDEGREE\ OF\ DISTORTION\ OF\ A\ TELEGRAPH |
CIRCUIT\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.11''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.11	%'
.ce 0
.sp 1P
.ce 1000
\fBIN\ TERMS\ OF\ THE\ DEGREES\ OF\ DISTORTION\ OF\ THE\ COMPONENT\ LINKS\fR 
.ce 0
.sp 1P
.ce 1000
\fI(New Delhi, 1960; amended at Geneva, 1964, 1980 and at Melbourne,\fR 
\fI1988)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.PP
\fB1\fR 
In general the isochronous standardized test distortion \(*d
(Definitions 33.07 and 33.12, 
Recommendation\ R.140 of a telegraph circuit
consisting of a number \fIn\fR of links in tandem lies between the arithmetic 
sum and the square root of the sum of the squares of the degrees of distortion 
of the individual links, 
\v'6p'
.sp 1P
.RT
.sp 1P
.ce 1000
@ pile { fIn\fR above sum above \fIi\fR~=1 } @ \(*d\fI
\di
\u\fR > \(*d >
\(sr
@ pile { fIn\fR above sum above \fIi\fR~=1 } @
\(*d\fI
\di
\u\fR \u2\d
$$we,
.ce 0
.sp 1P
.LP
.sp 1
.LP
\fIn\fR being the number of links in tandem. The few exceptions to this 
rule that have been observed related to extremely long circuits (for example, 
four links, each of approximately 3500\ km looped at voice\(hyfrequency 
at the distant end to give the equivalent of four links (each 7000\ km 
go and return) and a total 
length of approximately 28 | 00\ km on cable and open\(hywire carrier telephone\(hytype 
channels). 
.PP
\fB2\fR 
For such purposes as the planning of networks, the degree of
distortion of a telegraph circuit consisting of \fIn\fR channels or links 
in tandem in the telex service (where a great number of channels will be 
interconnected at random) is given fairly approximately by: 
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
\(*d
\dinherent
\u = 
$$So1
above sum above \fIn\fR $$Se \(*d\fI
\dc\u\fR +
\(sr
$$So\fIn\fR above sum above 1
$$Se
(\(*d
\dbias
\u)
\u2\d + 
$$So\fIn\fR above sum above 1
$$Se (\(*d
\dirreg.
\u)
\u2\d
$$we.
.ce 0
.sp 1P
.LP
.sp 1
.LP
Similarly, for the combination of a transmitter and a telegraph circuit
consisting of \fIn\fR channels or links in tandem in the telex service, 
the degree of distortion is given fairly approximately by: 
\v'6p'
.sp 1P
.ce 1000
\(*d
\dtext
\u = 
$$So\fIn\fR above sum above 1
$$Se \(*d\fI
\dc\u\fR +
\(sr
\(*d\fI
\dt\u\fR \u2\d + \(*d\fI
\dv\u\fR \u2\d +
$$So\fIn\fR above sum above 1
$$Se (\(*d
\dbias
\u)
\u2\d + 
$$So\fIn\fR above sum above 1
$$Se
(\(*d
\dirreg.
\u)
\u2\d
$$we,
.ce 0
.sp 1P
.LP
.sp 1
.LP
where
.LP
	\(*d
\s6inherent
.PS 10
	=
	the
probable degree of inherent start\(hystop distortion on standardized text,
.RT
.LP
	\(*d
\s6text
.PS 10
	=
	the probable degree of
gross start\(hystop distortion in service,
.RT
.LP
	\(*d\fI\fI\d\fIc\fR\u	=
	the degree of characteristic start\(hystop
distortion of a single channel or link,
.bp
.LP
	\(*d\fI\fI\d\fIt\fR\u	=
	the degree of synchronous start\(hystop
distortion of the transmitter,
.LP
	\(*d\fI\fI\d\fIv\fR\u	=
	the degree of start\(hystop distortion due solely to
the difference between the mean transmitter speed and the standardized
speed. (The difference to be considered is equal to six times the mean
difference for one element.)
.LP
	\(*d
\s6bias
.PS 10
	=
	 the degree of asymmetrical (bias) distortion of one channel measured 
using 1:1 or 2:2\ signals (either 1:1 or 
2:2\ signals should be used according to which is normally employed for
adjusting the channels),
.RT
.LP
	\(*d
\s6irreg.
.PS 10
	=
	the degree of fortuitous
distortion of one channel measured using 1:1 or 2:2\ signals.
.RT
.PP
\fB3\fR 
The values of distortion (except for \(*d\fI\fI\d\fIc\fR\u) inserted in 
the foregoing formulae must have the same probability of being exceeded 
(
\fIp\fR ). The degree of characteristic distortion \(*d\fI\fI\d\fIc\fR\uof 
a channel is fairly constant for each type of voice\(hyfrequency channel 
and can be 
determined in laboratory tests. Nevertheless, the maximum degree of
characteristic distortion is reached for only about 20% of the signals of
International Telegraph Alphabet\ No.\ 2. Empirical values for \(*d\fI\fI\d\fIc\fR\ucan 
be 
obtained with reasonable accuracy by using methods recommended by
Recommendation\ R.4.
.sp 9p
.RT
.PP
\fB4\fR 
The probability of exceeding the degrees of distortion
\(*d
\s6inherent
.PS 10
and \(*d
\s6text
.PS 10
calculated
with the aid of the above formulae is 0.2\ \fIp\fR .
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ The laws governing the addition of distortion in tandem 
connected code\(hyindependent time\(hy 
division\ multiplex systems, and in
particular the duration of measurement to be assumed, are the subject of
study.
.PP
Pending further study and mores specific advice, arithmetic
addition of distortion can be safely assumed for simplicity in all cases.
Although pessimistic this will not lead to unnecessarily restrictive
planning decisions in those cases where there is a regenerative link in the
chain,\ e.g., Recommendation\ R.101 TDM or a regenerative SPC exchange. 
However, where another law is known to apply then the appropriate law of 
addition can be used. 
.RT
.LP
e.g.:
.LP
mcvft
	\(em
	see text of Recommendation above
.LP
code\(hyindependent tdm
	\(em
	see note above for non\(hysynchronized tandemed
systems
.LP
	\(em
	for synchronized tandemed systems the distortion
due to the multiplexing process will be that of a
single system
.LP
code\(hydependent tdm
	\(em
	regenerative
.LP
.rs
.sp 21P
.ad r
Blanc
.ad b
.RT
.LP
.bp
.LP
\fBMONTAGE: PAGE 8 = PAGE BLANCHE\fR 
.sp 1P
.RT
.LP
.bp
.sp 1P
.ce 1000
\v'3P'
SECTION\ 2
.ce 0
.sp 1P
.ce 1000
\fBVOICE\(hyFREQUENCY\ TELEGRAPHY\fR 
.ce 0
.sp 1P
.sp 2P
.LP
\fBRecommendation\ R.20\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTELEGRAPH\ MODEM\ FOR\ SUBSCRIBER\ LINES\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.20''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.20	%'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1980; amended at Malaga\(hyTorremolinos, 1984 and at\fR  |
\fIMelbourne, 1988)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a)
that the use of high\(hylevel telegraph transmission with single or double 
current may cause disturbing impulse noise in adjacent cable pairs that 
may be eliminated by applying low\(hylevel transmission with telegraph 
modems; 
.LP
.PP
(b)
that telegraph modems would substantially reduce the
power consumption in the central office;
.PP
(c)
that where connection to a subscriber has to be achieved over a non\(hymetallic 
pair (e.g.,\ a 
voice\(hychannel frequency\(hydivision multiplex or pulse code modulation 
system) a telegraph modem has to be utilized; 
.PP
(d)
that the frequencies given below are already
standardized in Recommendation\ V.21\ [1];
.PP
(e)
that suitable inexpensive telegraph modems can be used for full duplex 
transmission on 2\(hywire circuits at modulation rates up to 
300\ bauds;
.sp 1P
.LP
\fIunanimously declares the view\fR 
.sp 9p
.RT
.PP
that where low\(hylevel telegraph transmission is used, the following method 
of transmission should be recommended for all modulation rates up to 
300\ bauds.
.RT
.sp 2P
.LP
\fB1\fR 	\fBChannel allocation\fR 
.sp 1P
.RT
.PP
The method of transmission is based on Recommendation V.21\ [1]
with the following frequency 
designations:
.RT
.LP
	Central\ office\ to\ subscriber\ (channel\ 1)
	F\dA\u\ =\ 1180\ Hz,
.LP
F\dZ\u\ =\ \ 980\ Hz;
.LP
	Subscriber\ to\ central\ office\ (channel\ 2)
	F\dA\u\ =\ 1850\ Hz,
.LP
F\dZ\u\ =\ 1650\ Hz.
.PP
The characteristic frequencies as measured at the telegraph modem line 
output should not differ by more than \(+- | \ Hz from the nominal figures. 
.PP
The modem shall continue to operate with a \(+- |  Hz change in receive
frequency.
.PP
It should be noted that there is equipment in use that applies
alternative frequencies to those shown in this Recommendation.
.bp
.RT
.sp 2P
.LP
\fB2\fR 	\fBInterface\fR 
.sp 1P
.RT
.PP
Where the modem is a separate, self\(hycontained unit, the following interchange 
circuits shall be used: 
.PP
Common return (e.g. circuit 102 in Recommendation V.24\ [2])
.PP
Transmitted data (e.g. circuit 103 in Recommendation V.24\ [2])
.PP
Received data (e.g. circuit 104 in Recommendation V.24\ [2])
.PP
Carrier detect (e.g. circuit 109 in Recommendation V.24\ [2])
.FS
This  is considered optional, particularly at the subscriber's location.
.FE
.
.RT
.sp 2P
.LP
\fB3\fR 	\fBElectrical characteristics\fR 
.sp 1P
.RT
.PP
The electrical characteristics (for stand alone telegraph modems) of the 
interchange circuits, should be in accordance with CCITT 
Recommendation\ V.28\ [3].
.RT
.sp 2P
.LP
\fB4\fR 	\fBPerformance\fR 
.sp 1P
.RT
.PP
4.1
The modem under test shall be connected to another modem
(according to this Recommendation or to Recommendation\ V.21) via an attenuator 
having a return loss of 4\ dB and an insertion loss of 30\ dB. The relative 
group\(hydelay characteristics of the transmit filters are subject to further
study.
.sp 9p
.RT
.PP
4.2
Uniform spectrum Gaussian noise (band limited to 10 kHz) shall be added 
to give a normalized signal\(hyto\(hynoise ratio of 32\ dB. 
This is defined as:
\v'6p'
.sp 9p
.RT
.sp 1P
.ce 1000
$$Bosignal energy per bit
} over { oise power per herts
$$Be =
$$Bosignal power
} over { oise power
$$Be \(mu
$$Bonoise bandwidth
} over { ignal bit rate
$$Be = 32 dB
.ce 0
.sp 1P
.LP
.sp 1
.PP
4.3
Test signals to Recommendation R.51 | fIbis\fR (QKS) shall be sent at a 
\(em13\ dBm transmit level in both directions simultaneously. (To ensure 
incoherence, the rate of the test signals for the direction not under test
shall be slightly lower.) The test period shall be 15\ seconds.
.sp 9p
.RT
.PP
The performance shall be in accordance with Table\ 1/R.20.
.ce
\fBH.T. [T1.20]\fR 
.ce
TABLE\ 1/R.20
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(60p) sw(60p) sw(60p) , ^  | c s 
^  | ^  | ^  | c 
^  | c | c | c.
Transit rate  (bit/s)	 {
Maximum isochronous distortion (%)
 }
	140 or 2600 ohm line	600 ohm line	No frequency error	\(+-6 Hz frequency error	No frequency error
_
.T&
lw(48p) | cw(60p) | cw(60p) | cw(60p) .
\ 50	\ 5	\ 7	\ 3
.T&
lw(48p) | cw(60p) | cw(60p) | cw(60p) .
\ 75	\ 6	\ 8	\ 4
.T&
lw(48p) | cw(60p) | cw(60p) | cw(60p) .
100	\ 7	10	\ 5
.T&
lw(48p) | cw(60p) | cw(60p) | cw(60p) .
110	\ 7	10	\ 5
.T&
lw(48p) | cw(60p) | cw(60p) | cw(60p) .
134.5	\ 8	12	\ 6
.T&
lw(48p) | cw(60p) | cw(60p) | cw(60p) .
150	\ 9	13	\ 6
.T&
lw(48p) | cw(60p) | cw(60p) | cw(60p) .
200	11	16	\ 8
.T&
lw(48p) | cw(60p) | cw(60p) | cw(60p) .
300	15	22	11
_
.TE
.nr PS 9
.RT
.ad r
\fBTable 1/R.20 [T1.20], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
4.4
In certain configurations, it is not possible to check the
modem
distortion, e.g.\ telegraph terminals, multiplex and switching equipment with
integral telegraph modems on which the d.c.\ signal output of the telegraph
modem is inaccessible for any reason. The performance will normally be 
in the form of a test for distortion margin before errors are output from 
the 
equipment.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ The modem needs only be tested at the maximum modulation 
rate of the equipment into which it is to be incorporated. 
.PP
4.5
The design of the telegraph modem shall be such that the
transmission performance is guaranteed without adjustment on installation or
subsequently.
.sp 9p
.RT
.sp 2P
.LP
\fB5\fR 	\fBLine signal levels and terminating impedance\fR 
.sp 1P
.RT
.PP
The line interface of the modem shall be balanced and shall present an 
impedance of 600\ ohms with a return loss (reference 600\ ohms resistive) 
of not less than 14\ dB (reflection coefficient no greater than\ 20%) over 
the range 300\(hy3400\ Hz. 
.RT
.sp 2P
.LP
5.1
	\fIOutput signal level\fR 
.sp 1P
.RT
.PP
5.1.1
When terminated in 600 ohms the output level should be set to   \(em13\ dBm.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ In certain applications, in particular if carrier
circuits for voice channel frequency division multiplex or pulse code
modulation systems are used (where the input level should be limited to
\(em13\ dBmO) it
may be necessary to have a setting range of output level which could give 
up to 0\ dBm. 
.PP
5.1.2
The difference in output levels between the Binary\ 1
(condition\ Z) and Binary\ 0 (condition\ A) signals shall not be greater 
than 1\ dB for either of the channels. 
.sp 9p
.RT
.sp 2P
.LP
5.2
	\fIReceive signal level\fR 
.sp 1P
.RT
.PP
5.2.1
When the received signal level is \(em43 dBm or greater, the
equipment should correctly interpret the line condition as either \fIF\fR\d\fIA\fR\uor 
\fIF\fR\d\fIZ\fR\u.
.sp 9p
.RT
.PP
5.2.2
When the received signal level remains below a threshold between \(em45\ 
dBm and \(em48\ dBm, the equipment shall ignore incoming information within 
300\ ms of the signal level dropping below the threshold. During this delay 
the receiving equipment may interpret (correctly or incorrectly) characters 
received after the drop in received signal level below the threshold.
Thereafter, the equipment should not interpret characters received until the
received signal level has restored to at least 2\ dB above the threshold. 
If the signal level drops below the threshold for less than 10\ ms, the 
equipment 
should take no action.
.PP
5.2.3
Once the received signal level has fallen below the threshold
value, the equipment shall ignore any subsequent increases in the signal 
level which are either less than 2\ dB above the threshold or of more than 
2\ dB above the threshold but less than 10\ ms in duration. 
.PP
\fINote\ 1\fR \ \(em\ The requirements of \(sc\ 5.2.3 need not apply during 
the first 20\ ms from the fall in received signal level below the threshold. 
.PP
\fINote\ 2\fR \ \(em\ The signal level detector shall respond to the total 
power contained within the nominal spectrum of the received line signal. 
.RT
.sp 2P
.LP
\fB6\fR 	\fBMaintenance facilities\fR 
.sp 1P
.RT
.PP
Maintenance facilities, e.g. test loops, are a national
matter.
.RT
.sp 2P
.LP
\fB7\fR 	\fBProtection against high voltages\fR 
.sp 1P
.RT
.PP
The equipment shall withstand residual lightning surges, high
voltage line faults, and high level telegraph keying. The protection required 
is considered a national matter, though in some cases Recommendation\ K.21 
could be applied\ [4]. 
.bp
.RT
.LP
.rs
.sp 24P
.ad r
\fBFigure 1/R.20, p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fB8\fR 	\fBLine wetting\fR 
.sp 1P
.RT
.PP
8.1
Line wetting, where required by the type of line plant used,
will normally be sourced by the in\(hystation equipment and looped by the
subscriber's equipment.
.sp 9p
.RT
.PP
8.2
The current has a maximum value of 15 mA with the line
short\(hycirucited. The wetting current shall be a minimum of 5\ mA on 
4000\(hyohm 
lines. The open circuit voltage shall be under 80\ V.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ In some countries, other values may apply.
.PP
Where a modem may be required to work in the presence of line wetting, 
then the modem performance (see \(sc\ 4) and the modem line impedance (see 
\(sc\ 5) 
requirements must apply with line wetting current flowing.
.PP
The noise applied to the line from the wetting power supply shall be under 
\(em80\ dBm (600\ ohms) over a range 300 to\ 3400\ Hz (flat). 
.RT
.sp 2P
.LP
\fB9\fR 	\fBPermitted out\(hyof\(hyband energy\fR 
.sp 1P
.RT
.PP
9.1
The out\(hyof\(hyband energy is a national matter; however the
following information is provided to assist equipment manufacturers:
.sp 9p
.RT
.PP
9.2
The transmitted signal level (with an output level at \(em13\ dBm)  at
any one frequency shall not exceed the following limits (with the forward 
and reverse channel keyed at 300\ bit/s with a QKS code): 
.sp 9p
.RT
.LP
	200\ Hz\ to\ 3200\ Hz
	\(em13\ dBm
.LP
	100\ Hz\ to\ 200\ Hz\ and\ 3200\ Hz\ to\ 3400\ Hz
	\(em23\ dBm
.LP
	Below\ 100\ Hz
	\(em33\ dBm
.LP
	Above\ 3400\ Hz
	\(em33\ dBm
	and decreasing by
12\ dB/octave to \(em67\ dBm
.bp
.sp 2P
.LP
	\fBReferences\fR 
.sp 1P
.RT
.LP
[1]
	CCITT Recommendation \fI300 bits per second duplex modem standardized\fR 
\fIfor use in the general switched telephone network\fR , Rec.\ V.21.
.LP
[2]
	CCITT Recommendation \fIList of definitions for interchange circuits\fR 
\fIbetween data terminal equipment and data circuit terminating equipment\fR ,
Rec.\ V.24.
.LP
[3]
	CCITT Recommendation \fIElectrical characteristics for unbalances\fR 
\fIdouble\(hycurrent interchange circuits\fR , Rec.\ V.28.
.LP
[4]
	CCITT Recommendation \fIResistibility of subscribers' terminals to\fR 
\fIover\(hyvoltages and over\(hycurrents\fR , Rec.\ K.21.
\v'6p'
.sp 2P
.LP
\fBRecommendation\ R.30\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBTRANSMISSION\ CHARACTERISTIC\ FOR\ \fR \fBINTERNATIONAL\ VFT\ LINKS\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.30''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.30	%'
.ce 0
.sp 1P
.ce 1000
\fI(Mar del Plata, 1968; amended at Geneva, 1976)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.PP
\fB1\fR 
Standardized carrier systems with 4\(hykHz and 3\(hykHz spacing
permit homogeneous voice\(hyfrequency telegraph (VFT) systems providing the
capacities of telegraph channels given in Table\ 1/R.30.
.sp 1P
.RT
.ce
\fBH.T. [T1.30]\fR 
.ce
TABLE\ 1/R.30
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) | cw(48p) | cw(48p) | cw(48p) | cw(48p) .
Bearer bandwidth	50\(hybaud  120\(hyHz spacing	100\(hybaud 240\(hyHz spacing	200\(hybaud 360\(hyHz spacing	200\(hybaud 480\(hyHz spacing
_
.T&
cw(36p) | cw(48p) | cw(48p) | cw(48p) | cw(48p) .
4 kHz	24	12	8  (not normally used)	6
_
.T&
cw(36p) | cw(48p) | cw(48p) | cw(48p) | cw(48p) .
3 kHz	22	11	7	5
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLE 1/R.30 [T1.30], p.\fR 
.sp 1P
.RT
.ad b
.RT
.PP
\fB2\fR 
Audio\(hyfrequency circuits with heavy or semi\(hyheavy loading permit 
12\(hychannel 50\(hybaud systems; circuits with lighter loading permit 
18\ channels at 50\ bauds. 
.sp 9p
.RT
.LP
.PP
\fB3\fR 
Four\(hywire links are to be preferred for voice\(hyfrequency
telegraphy.
.sp 9p
.RT
.PP
\fB4\fR 
The composition of a 4\(hywire link for voice\(hyfrequency telegraphy differs 
from that of a telephone circuit in that there are no terminating sets, 
signalling equipment and echo suppressors. 
.sp 9p
.RT
.PP
\fB5\fR 
With 2\(hywire links, a duplex arrangement would not be feasible
since the links could not be balanced with the necessary precision to avoid
mutual interaction. If the low frequencies are used for transmission in one
direction and high frequencies for the other direction, a 2\(hywire link can be
used for voice\(hyfrequency telegraphy.
.sp 9p
.RT
.PP
\fB6\fR 
The conditions of use of international VFT links are described in detail 
in Recommendation\ H.22\ [1]. 
.bp
.sp 9p
.RT
.PP
\fB7\fR 
PCM (pulse code modulation) channels complying with
Recommendation\ G.712\ [2] are also suitable as bearers for FMVFT
(frequency\(hymodulated voice\(hyfrequency telegraph) links. However, the 
increase 
in telegraph distortion in relation to the transmission level and the number 
of tandem\(hyconnected PCM channels is the subject of further study. 
.sp 9p
.RT
.LP
.sp 2P
.LP
	\fBReferences\fR 
.sp 1P
.RT
.LP
[1]
	CCITT Recommendation \fITransmission requirements of international\fR 
\fIvoice\(hyfrequency telegraph links (at\ 50, 100 and 200\ bauds)\fR ,
Rec.\ H.22.
.LP
[2]
	 CCITT Recommendation \fIPerformance characteristics of PCM channels at\fR 
\fIaudio frequencies\fR , Rec.\ G.712. 
\v'6p'
.LP
.sp 2P
.LP
\fBRecommendation\ R.31\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSTANDARDIZATION\ OF\ \fR \fBAMVFT\ SYSTEMS\fR \ \fBFOR |
A\ MODULATION\ RATE\ OF\ 50\ BAUDS\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.31''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.31	%'
.ce 0
.sp 1P
.ce 1000
\fI(Mar del Plata, 1968, incorporating former Recommendations R.31,\fR 
\fIR.32 and R.34;\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIamended at Malaga\(hyTorremolinos, 1984)\fR 
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 2P
.LP
\fIunanimously declares the following view\fR :
.sp 1P
.RT
.PP
\fB1\fR It is advisable to adopt, for amplitude\(hymodulated
voice\(hyfrequency telegraph (AMVFT) systems and for a modulation rate not
exceeding 50\ bauds, the series of frequencies formed by odd multiples 
of 60\ Hz, the lowest frequency being 420\ Hz as shown in Table\ 1/R.31. 
.sp 9p
.RT
.ce
\fBH.T. [T1.31]\fR 
.ce
TABLE\ 1/R.31
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
Channel position	Frequency  Hz	Channel  position	Frequency  Hz
_
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 1	\ 420	13	1860
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 2	\ 540	14	1980
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 3	\ 660	15	2100
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 4	\ 780	16	2220
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 5	\ 900	17	2340
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 6	1020	18	2460
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 7	1140	19	2580
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 8	1260	20	2700
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
\ 9	1380	21	2820
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
10	1500	22	2940
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
11	1620	23	3060
.T&
cw(30p) | cw(42p) | cw(30p) | cw(42p) .
12	1740	24	3180
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLE 1/R.31 [T1.31], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.sp 1
.PP
\fB2\fR This numbering is valid whatever use is made of the channel
(e.g. traffic channel, pilot channel,\ etc.) or the method employed to obtain
the line frequencies, e.g.\ by group modulation. For the numbering of
channels that has been adopted in the international service see
Recommendation\ R.70 | fIbis\fR .
.bp
.sp 9p
.RT
.PP
\fB3\fR In the case of systems on telephone\(hytype circuits with a
spacing of 3\(hykHz operating in accordance with the standardized frequency
series, channel positions\ 23 and 24 cannot be used.
.sp 9p
.RT
.PP
\fB4\fR The frequencies applied to the telephone\(hytype circuit that is
used as the voice\(hyfrequency telegraph bearer circuit should not deviate by
more than 6\ Hz from the nominal value when the telegraph channels supplied 
are operating over a telephone\(hytype circuit composed exclusively of 
audio\(hyfrequency sections, and not more than 3\ Hz in other cases. 
.sp 9p
.RT
.PP
\fB5\fR The power levels of carrier waves transmitted on the line and
measured successively in as short a period as possible should not differ 
from one another by more than 1.74\ dB when they are operating on a constant 
impedance.
.sp 9p
.RT
.PP
\fB6\fR The power of each of the carrier waves transmitted on the line
should not vary in operation by more than \(+- | .87\ dB when it operates on a
constant impedance.
.sp 9p
.RT
.PP
\fB7\fR The amplitude of the signals transmitted by a channel modulator 
during a transition from condition\ A to condition\ Z should remain 
within the tolerances of Figure\ 1/R.31 in which the values \fIt\fR\d0\uand 
\fIy\fR\d2\uand \fIy\fR\d1\uare fixed as follows: 
.sp 9p
.RT
.LP
	\fIt\fR\d0\u\ =\ \ 11\ ms,
.LP
	\fIy\fR\d1\u\ =\ \ 95%,
.LP
	\fIy\fR\d2\u\ =\ 110%.
.LP
.rs
.sp 27P
.ad r
\fBFIGURE 1/R.31, p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.bp
.PP
\fB8\fR Receivers with rapid\(hyaction level correction should not be so
sensitive to secondary pulses following the signal pulse provided that the
amplitude of the signal emitted does not exceed the reference level by
more than\ 10% and that the reference level does not exceed the normal 
level by 10.4\ dB. (This provision applies only to new systems.) 
.sp 9p
.RT
.PP
\fB9\fR If 1:1 reversals at frequency \fIf\fR\d\fIp\fR\ucorresponding to the
modulation rate are sent over a channel with mid\(hyfrequency \fIF\fR\d0\u, 
the voltage at frequency \fIF\fR\d0\u\ \(+-\ 3\ \fIf\fR\d\fIp\fR\umust 
not exceed 3% of the nominal 
voltage at frequency \fIF\fR\d0\uand the voltage at the frequencies
\fIF\fR\d0\u\ \(+-\ 5\ \fIf\fR\d\fIp\fR\umust not exceed 0.4% of the nominal 
voltage at frequency 
\fIF\fR\d0\u.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ These tolerances will be required only for future systems. 
Administrations should try as far as possible to use systems satisfying 
these tolerances on international relations. 
.PP
\fB10\fR The unbalance of the emitted signal should not be greater than
\(+- | % (methods of measuring this unbalance are described in\ [1] and\ [2]).
This tolerance takes account of the
limit in \(sc\ 11\ below for new systems.
.sp 9p
.RT
.PP
\fB11\fR For new systems, the static relay should introduce a
difference of not less than 45\ dB between the two signalling conditions. 
(For existing systems the limit is 30\ dB.) 
.sp 9p
.RT
.LP
.PP
\fB12\fR In the event of failure of the control current in the sending
static relay, the attenuation of the residual signal relative to this nominal 
level should be at least 27\ dB. This attenuation of the signal need not 
occur immediately on the failure of the control current. 
.sp 9p
.RT
.PP
\fB13\fR Systems should be able to tolerate slow level variations of at
least \(+- | \ dB. Administrations should equip systems that are unable to
tolerate such variations with a common amplifier to enable them to tolerate
variations of at least \(+- | \ dB.
.sp 9p
.RT
.PP
\fB14\fR The permissible limit for the power of the telegraph signal on
each telegraph channel when a continuous tone is being transmitted is given 
in Table\ 2/R.31. 
.sp 9p
.RT
.ce
\fBH.T. [T2.31]\fR 
.ce
TABLE\ 2/R.31
.ce
\fBNormal limits (nominal values) for the power per telegraph
.ce
channel in AMVFT systems\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(108p) | cw(60p) sw(60p) , ^  | c | c.
 {
Number of telegraph channels in the AMVFT system 
 }	 {
Allowable power per telegraph channel
at a point of zero relative
level
when sending a signal corresponding to
continuous Z condition
 }
	microwatts	decibels
_
.T&
lw(108p) | cw(60p) | cw(60p) .
12 or less	35	\(em14.5\ 
_
.T&
lw(108p) | cw(60p) | cw(60p) .
18	15	\(em18.3\ 
_
.T&
lw(108p) | cw(60p) | cw(60p) .
24	\ 9	\(em20.45
.TE
.LP
\fINote\fR
\ \(em\ These limits are such that the maximum instantaneous voltage will
exceed that of a sinusoidal voltage with a power of 5 milliwatts at a point of zero relative level. This is the maximum permissible for voice\(hyfrequency
circuits.
.nr PS 9
.RT
.ad r
\fBTABLE 2/R.31 [T2.31], p. 
.sp 1P
.RT
.ad b
.RT
.PP
.sp 1
\fB15\fR Audio\(hyfrequency is transmitted to line when stop polarity
(condition\ Z) is sent.
.bp
.sp 9p
.RT
.LP
.PP
\fB16\fR When a signal, whose frequency is equal to the nominal
frequency of the channel and whose level is 18.3\ dB below the normal signal
level of the channel, is applied to the detector of a 24\(hychannel AMVFT 
system, the receiving relay should not respond. 
.sp 9p
.RT
.PP
\fB17\fR It must be possible to subject any channel to a test without
withdrawing from service a channel other than the return channel of the 
circuit planned. 
.sp 9p
.RT
.PP
\fB18\fR In graded harmonic frequency telegraphy, it is desirable
that the same frequencies be used separately for circuits established on
different successive sections of a 4\(hywire circuit.
.sp 9p
.RT
.PP
\fB19\fR In graded harmonic frequency telegraphy, the attenuation of
the filters that pass a group of frequencies must, in the suppressed frequency 
band, be higher by at least 35\ dB than that shown in the transmission 
band. 
.sp 9p
.RT
.PP
\fB20\fR In graded harmonic frequency telegraphy, in order to facilitate 
local tests, the frequencies used for communications set up between two 
international offices in one direction should also be used in the opposite
direction, if possible.
.sp 9p
.RT
.sp 2P
.LP
	\fBReferences\fR 
.sp 1P
.RT
.LP
[1]
	 \fIMeasuring method to determine the asymmetry of an amplitude\(hymodulated\fR 
\fItelegraph signal\fR , Blue\ Book, Vol.\ VII, Supplement No.\ 11, ITU, 
Geneva,\ 1964. 
.LP
[2]
	\fIThe measurement of the distortion produced in the sending terminal\fR 
\fIequipment of an A.M.\(hyV.F. telegraph system\fR , Blue\ Book, Vol.\ 
VII, Supplement No.\ 12, ITU, Geneva,\ 1964. 
\v'1P'
.LP
.sp 2P
.LP
\fBRecommendation\ R.35\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSTANDARDIZATION\ OF\ \fR \fBFMVFT\ SYSTEMS\fR  | fR \fBFOR\ A\ MODULATION\ 
RATE\ OF\ 50\ BAUDS\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.35''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.35	%'
.ce 0
.sp 1P
.ce 1000
\fI(former CCIT Recommendation B.48, Geneva, 1956; amended\fR \fIat New 
Delhi, 1960,\fR 
.sp 9p
.RT
.ce 0
.ce 1000
\fIGeneva, 1964, Mar del Plata, 1968, Geneva, 1972, 1976, 1980,\fR 
.ce 0
.sp 1P
.ce 1000
\fIMalaga\(hyTorremolinos, 1984 and at Melbourne, 1988)\fR 
.ce 0
.sp 1P
.PP
\fINote\fR \ \(em\ In this Recommendation, frequency\(hymodulated
voice\(hyfrequency telegraph (FMVFT) equipment with and without crystal 
control are distinguished. In order to improve the quality of transmission 
and to 
minimize maintenance costs, the application of equipment with crystal control 
is recommended. 
.sp 1P
.RT
.PP
\fB1\fR 
The nominal modulation rate should be standardized at
50\ bauds.
.sp 9p
.RT
.LP
.PP
\fB2\fR 
For the nominal mean frequencies, the series formed by the odd multiples 
of 60\ Hz should be adopted, the lowest frequency being 420\ Hz in 
accordance with Recommendation\ R.31, \(sc\ 1, the mean frequency \fIF\fR\d0\ubeing 
defined as half the sum of the two characteristic frequencies corresponding 
to the permanent start polarity \fIF\fR\d\fIA\fR\uand stop polarity \fIF\fR\d\fIZ\fR\u. 
For the numbering of channels that has been adopted in the international 
service, see Recommendation\ R.70 | fIbis\fR . 
.sp 9p
.RT
.PP
\fB3\fR 
The mean frequencies at the sending end should not deviate from their nominal 
value by more than: 
.sp 9p
.RT
.LP
	a)
	for equipment without crystal control 2\ Hz;
.LP
The tightening of this tolerance is for further study.
.FE
	b)
	for equipment with crystal control 0.5\ Hz.
.bp
.PP
\fB4\fR 
The unbalance due to the modulation process
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
should not exceed 2%,
.sp 9p
.RT
.LP
where
.LP
	\fIF\fR  | 
\fI
\dA\u\fR \ and\ 
\fIF\fR  | 
\fI
\dZ\u\fR 	are
the two characteristic frequencies measured over a period of 10\ s;
.LP
	\fIF\fR  | 
\d0\u
	is the mean static frequency
measured =
$$1o\fIF\fR  | 
\fI
\dA\u\fR + \fIF\fR  | 
\fI
\dZ\u\fR $$1u2
$$1e;
.LP
	\fIF\fR\d\fIl\fR\u	is the mean dynamic frequency measured with 1:1
rectangular signals during 10\ s.
.PP
Measurement should be made applying to the input of the
transmitter\ 1:1 rectangular signals with the build\(hyup and hangover time
below 1\ \(*ms and with the unbalance below 0.1%. In the event that in 
service the transmitter is controlled by an electro\(hymechanical relay 
(with a certain 
transit time), the measurement should also be made with that type of relay
inserted between the 1:1\ signal generator and the input to the transmitter.
Both forms of measurements need not necessarily be included in the maintenance 
procedure but should be included in laboratory type tests. 
.PP
\fINote\fR \ \(em\ To determine the unbalance due to the modulation process by
the method indicated above, it is necessary to measure the
frequencies\ \fIF\fR  | 
\fI
\dA\u\fR , \fIF\fR  | 
\fI
\dZ\u\fR and \fIF\fR\d\fIl\fR\uand to calculate the mean frequency\ \fIF\fR  | 
\d0\u
and the
unbalance
\v'6p'
.RT
.sp 1P
.ce 1000
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
.ce 0
.sp 1P
.LP
.sp 1
.PP
A more rapid method for checking whether or not the unbalance is
less than the limit fixed is to measure:
.LP
	\(em
	the mean dynamic frequency\ \fIF\fR\d\fIl\fR\u\ with 1:1\ signals during
10\ seconds;
.LP
	\(em
	the mean dynamic frequency\ \fIF\fR\d\fIm\fR\u\ with 2:2\ signals during
10\ seconds;
\v'6p'
.sp 1P
.ce 1000
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e = 4
$$1 | fIF\fR  | 
\d0\u
\(em
\fIF
\dm\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em \fIF\fR  | 
\fI
\dZ\u\fR $$1e
.ce 0
.sp 1P
.LP
.sp 1
or to subtract:
\v'6p'
.sp 1P
.ce 1000
| fIF\fR \fI
\dl\u\fR \(em \fIF
\dm\u\fR | = 
$$Bo1
} over { 
$$Be (\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR ) \(*d \( = 
$$Bo1
} over { 
$$Be (\fIF
\dA\u\fR \(em
\fIF
\dZ\u\fR ) | (*d \(= 0.4 Hz.
.ce 0
.sp 1P
.LP
.sp 1
.PP
The absolute value of the difference between the two frequencies
measured, \fIF\fR\d\fIl\fR\u\ and \fIF\fR\d\fIm\fR\u,\ must be less than 
0.4\ Hz. 
.PP
\fB5\fR 
The difference between the two characteristic frequencies
(corresponding to the start and the stop conditions) should be 60\ Hz.
.sp 9p
.RT
.PP
\fB6\fR 
The maximum tolerance on this difference should be \(+- | \ Hz.
.sp 9p
.RT
.PP
\fB7\fR 
The total average power transmitted to the telephone\(hytype
circuit is normally dependent on the transmission characteristics of the
circuit as follows:
.sp 9p
.RT
.LP
	a)
	For circuits with characteristics not exceeding the limits
given in Annex\ A, the total average
power transmitted by all channels of a system should preferably
be limited to 50\ \(*mW at a point of zero relative level.
This sets, for the average power of a telegraph channel (at a
point of zero relative level), the limits given in Table\ 1/R.35.
.LP
	b)
	For other circuits, the total average power transmitted by
all channels of a system is limited to 135\ \(*mW at a
point of zero relative level. This sets, for the average power
of a telegraph channel (at a point of zero relative level), the
limits given in Table\ 2/R.35.
.bp
.ce
\fBH.T. [T1.35]\fR 
.ce
TABLE\ 1/R.35
.ce
\fBNormal limits (nominal values) for the power per telegraph channel
.ce
in FMVFT systems for bearer circuits\fR 
.ce
\fBwith charactistics not
.ce
exceeding the limits given in Annex A\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(108p) | cw(60p) sw(60p) , ^  | c | c.
 {
Number of telegraph channels in the FMVFT system
 }	 {
Allowable power per telegraph channel
at a point of zero relative
level
 }
	in microwatts	 {
in absolute power level 
decibels
 }
_
.T&
lw(108p) | cw(60p) | cw(60p) .
12 or less	4.0	\(em24.0
_
.T&
lw(108p) | cw(60p) | cw(60p) .
18	2.7	\(em25.7
_
.T&
lw(108p) | cw(60p) | cw(60p) .
24	2.0	\(em27.0
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLE 1/R.35 [T1.35], p.\fR 
.sp 1P
.RT
.ad b
.RT
.ce
\fBH.T. [T2.35]\fR 
.ce
TABLE\ 2/R.35
.ce
\fBNormal limits (nominal values) for the power per telegraph channel
.ce
\fR 
.ce
\fBin FMVFT systems for others bearer circuits
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(108p) | cw(60p) sw(60p) , ^  | c | c.
 {
Number of telegraph channel in the FMVFT system
 }	 {
Allowable power per telegraph channel
at a point of zero
relative level
 }
	in microwatts	 {
in absolute power level
decibels
 }
_
.T&
lw(108p) | cw(60p) | cw(60p) .
12 or less	10.8	\(em19.7
_
.T&
lw(108p) | cw(60p) | cw(60p) .
18	\ 7.2	\(em21.4
_
.T&
lw(108p) | cw(60p) | cw(60p) .
24	\ 5.4	\(em22.7
.TE
.LP
\fINote\fR
\ \(em\ The figures in Tables 1/R.35 and 2/R.35 assume the provision of a
pilot channel on the telegraph bearer at a level of
\(em27 dBm0 and \(em22,7 dBm0 respectively.
.nr PS 9
.RT
.ad r
\fBTable 2/R.35 [T2.35], p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
.sp 2
.PP
\fB8\fR 
In service, the levels of the signals corresponding to
continuous condition\ Z and continuous condition\ A should not differ by more
than 1.7\ dB in the same channel. Both of these levels must lie between 
\(+- | .7\ dB with reference to the level given in Table\ 1/R.35 or Table\ 
2/R.35 as 
applicable.
.sp 9p
.RT
.PP
\fB9\fR 
The frequency for the transmitted condition corresponding to the condition\ 
A is the higher of the two characteristic frequencies and that 
corresponding to the condition\ Z is the lower.
.sp 9p
.RT
.PP
\fB10\fR In the absence of a channel\(hymodulator control telegraph current, 
a frequency should be transmitted within \(+- | \ Hz of the frequency normally 
transmitted for the start polarity. This frequency need not be sent immediately 
after interruption of the control current. 
.bp
.sp 9p
.RT
.PP
\fB11\fR 
The frequency spectrum of the emitted signal, when
transmitting 1:1 reversals (Definition 31.401, Recommendation\ R.140) at the
modulation rate of 2\ \fIf\fR\d\fIp\fR\u(\fIf\fR\d\fIp\fR\u\ =\ frequency 
of modulation), should be in accordance with the limits specified in Figure\ 
1/R.35, which shows the levels of the spectra of different components with 
respect to the amplitude of the 
non\(hymodulated carrier as ordinates and the frequencies as abscissae.
.sp 9p
.RT
.PP
\fB12\fR The receiving equipment should operate satisfactorily when the 
receiving level falls to 17.4\ dB below the nominal level. The receiving 
equipment should have been restored to condition\ A when the receiving level
has fallen to 23.5\ dB below the nominal level. The nominal level is the 
level resulting from the choice of power per channel (see Tables\ 1/R.35 
or\ 2/R.35 as applicable) depending 
upon the number of channels (12, 18 or 24) on the circuit. The alarm\(hycontrol
level is left to the choice of each Administration.
.sp 9p
.RT
.PP
\fB13\fR On delivery by the manufacturer of 50\(hybaud FMVFT equipment,
the following values must not be exceeded for the degree of distortion on a
telegraph channel. These values correspond to closed circuit measurements, 
made with the audio\(hyfrequency line terminals of the sending and receiving 
equipments connected together through an artificial line. Before the series 
of 
measurements taken in accordance with 
Recommendation\ R.51, the levels are
adjusted to their normal values, the mean frequencies are checked to see
whether they are within:
.sp 9p
.RT
.LP
	1)
	for equipment without crystal control \(+- | \ Hz;
.LP
	2)
	for equipment with crystal control \(+- | .5\ Hz
,
.LP
of their nominal value (see \(sc\ 3 above) and the difference between the two
characteristic frequencies is within the permitted tolerance of less than 
3\ Hz (see \(sc\ 6 above). Bias distortion is eliminated by adjustment 
in the 
channel receivers. The other channels of the system are modulated with
unrelated signals when the effect of inter\(hychannel interference is to be
included in the measurement. These \*Qunrelated signals\*U can conveniently be
1:1\ signals from different generators at approximately 50\ bauds but not
synchronous to each other or to the signal on the channel under test.
.LP
	a)
	The transmission levels being normal, the artificial line
introducing no frequency drift, but the measured channel being subject to
fortuitous distortion due to interchannel interference: 5%\ for the degree of
inherent isochronous distortion.
.LP
	b)
	The level being maintained constant, but at a value different
from the normal level, for all constant levels between 8.7\ dB above the 
normal reception level and 17.4\ dB below the normal reception level, the 
other 
conditions being the original measurement condition: 7%\ for the degree of
inherent isochronous distortion.
.LP
	c)
	In the presence of interference by a single sine\(hywave frequency
equal first to one and then to the other characteristic frequency, with 
a level of 20\ dB below the signal level, the other conditions for the 
start of 
measurements being maintained: 12%\ for the degree of inherent isochronous
distortion (i.e.\ total distortion including the increase due to the interfering 
frequency, not distortion due to the interfering frequency alone). 
.LP
	d)
	By introducing a frequency drift (\(*D\fIf\fR \ Hz) of the signals
during transmission through the artificial line, \(*D\fIf\fR \ being not
more than 5\ Hz and the initial condition of the test otherwise
being preserved:
.LP
	\(em
	for\ equipment\ without\ crystal\ control
	?04
.LP
	\(em
	for\ equipment\ with\ crystal\ control\ but\ without
	?05\ \ (5\ +
2.5\ \(*D\fIf\fR Hz)\ %
.LP
	compensation\ for\ frequency\ drift
	\(rb
.LP
	\(em
	for\ equipment\ with\ crystal\ control\ and\ compensation
.LP
for frequency drift
	 |  \ 7%
.LP
	for the degree of inherent isochronous distortion.
.LP
	 By introducing a frequency drift (\(*D\fIf\fR \ Hz) of the signals during 
transmission through the artificial line, \(*D\fIf\fR being not more than 
10\ Hz, and the initial conditions of the test otherwise being preserved: 
.LP
	\(em
	for\ equipment\ with\ crystal\ control\ and\ compensation
.LP
for\ frequency\ drift
	 |  \ 13%
.LP
	for the degree of inherent isochronous distortion. The measurements
shall be made after the transient effects of changing frequency have
ceased.
.LP
	e)
	Equipment with crystal control, with any climatic conditions
specified for the tested equipment, the initial condition of
the test otherwise being preserved: 8%\ for the degree of
inherent isochronous distortion. The bias distortion caused
by changes of climatic conditions should not be eliminated.
.bp
.LP
.rs
.sp 36P
.ad r
\fBFIGURE 1/R.35, p.\fR 
.sp 1P
.RT
.ad b
.RT
.PP
\fB14\fR 
Frequency drifts on modern telephone\(hytype circuits are
generally less than 2\ Hz. Hence it is not necessary to recommend frequency
drift control. For circuits on which a maximum frequency drift of not greater 
than \(+- | \ Hz cannot be guaranted, and on which the distortion resulting 
from the frequency drift is not acceptable, compensation seems necessary. 
Two methods 
can be used:
.sp 9p
.RT
.LP
	a)
	compensation for each channel up to about 15\ Hz;
.LP
	b)
	compensation for all the channels by using a pilot. In this
case, the receiving end must be able to request and obtain a
pilot frequency. Administrations should agree among themselves
on the advisability of sending the pilot and the choice of
frequency. The frequencies 3300\ Hz or, preferably, 300\ Hz are recommended
for this pilot, with a tolerance of:
.LP
	1)
	for equipment without crystal control \(+- | \ Hz
.LP
	2)
	for equipment with crystal control \(+- | .2\ Hz.
.LP
	The mean power emitted at the relative zero point on this
frequency should not exceed \(em27.0\ dBm0 or \(em22.7\ dBm0 as appropriate 
(see 
Table\ 2/R.35).
.PP
\fB15\fR The number of significant modulation conditions is fixed at two; 
this number may be increased, if necessary, by agreement between the 
Administrations concerned.
.bp
.sp 9p
.RT
.ce 1000
ANNEX\ A
.ce 0
.ce 1000
(to Recommendation R.35)
.sp 9p
.RT
.ce 0
.ce 1000
\fBLimits required by a bearer circuit for FMVFT application if the\fR 
.sp 1P
.RT
.ce 0
.ce 1000
\fBtotal power transmitted by all channels is set at 50 microwatts\fR 
.ce 0
.LP
A.1
	\fILoss/frequency distortion\fR 
.sp 1P
.RT
.PP
The variation with frequency of the overall loss of the link with respect 
to the loss at 800\ Hz should not exceed the limits shown in 
Figure\ A\(hy1/R.35.
.RT
.LP
.rs
.sp 28P
.ad r
\fBFIGURE A\(hy1/R.35, p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
A.2
	\fIRandom noise\fR 
.sp 9p
.RT
.PP
The mean psophometric noise power referred to a point of zero
relative level should not exceed 32 | 00\ pW0p (\(em45\ dBm0p), using a 
psophometer in accordance with Recommendation\ P.53\ [1]. 
.RT
.sp 1P
.LP
A.3
	\fIImpulsive noise\fR 
.sp 9p
.RT
.PP
The number of counts of impulsive noise that exceeds \(em28\ dBm0
should not exceed\ 18 in 15\ minutes when measured with an impulsive noise
counter in accordance with Recommendation\ O.71\ [2].
.bp
.RT
.sp 1P
.LP
A.4
	\fIError rates\fR 
.sp 9p
.RT
.PP
The telegraph character error rate that may be caused by
interruptions and noise in the bearer circuit should not exceed the limits
stated in Recommendations\ R.54 and\ F.10\ [3].
.RT
.LP
.sp 2P
.LP
	\fBReferences\fR 
.sp 1P
.RT
.LP
[1]
	CCITT Recommendation \fIPsophometers (apparatus for the objective\fR 
\fImeasurement of circuit noise)\fR , Rec.\ P.53.
.LP
[2]
	 CCITT Recommendation \fISpecification for an impulsive noise measuring\fR 
\fIinstrument for telephone\(hytype circuits\fR , Rec.\ O.71. 
.LP
[3]
	CCITT Recommendation \fICharacter error rate objective for telegraph\fR 
\fIcommunication using 5\(hyunit start\(hystop equipment\fR , Rec.\ F.10.
\v'1P'
.LP
.sp 2P
.LP
\fBRecommendation\ R.35 | fR \fIbis\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fB50\(hyBAUD\ \fR \fBWIDEBAND\ VFT\ SYSTEMS\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.35^bis''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.35^bis	%'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
	The\ CCITT,
.sp 1P
.RT
.sp 1P
.LP
\fIconsidering\fR 
.sp 9p
.RT
.PP
(a) 
that Voice\(hyfrequency telegraph (VFT) systems standardized by the CCITT 
for 50\(hybaud channels are described in Recommendations\ R.31 (for 
amplitude modulation) and\ R.35 (for frequency modulation). Systems that 
comply with these Recommendations are those normally recommended by the 
CCITT. 
However, it may sometimes be advisable to use a VFT system for a speed of
50\ bauds in which the channels have wider spacing than in systems complying
with Recommendations\ R.31 and\ R.35,
.LP
.PP
(b)
that the use of channels with a spacing of more than
120\ Hz for a modulation rate of 50\ bauds offers certain advantages in the
following cases:
.LP
	i)
	on links with not much traffic (which it is not intended to
increase to more than 12\ channels for a long time to come);
.LP
	ii)
	 on links where channels are required to have less distortion than on 
channels established in accordance with 
Recommendations\ R.31 and\ R.35;
.LP
	iii)
	as far as maintenance is concerned, wideband equipment
requires less attention,
.PP
(c)
that in particular, if telephone\(hytype circuits carrying VFT systems 
are unstable, the use of wideband channels together with frequency modulation 
is recommended, 
.PP
(d)
Moreover that, if systems are standardized so that only one modulation 
method is used, the cost of equipment should be 
lower.
.LP
.sp 1P
.LP
\fIunanimously declares the view\fR 
.sp 9p
.RT
.PP
that when Administrations agree to set up a 50\(hybaud VFT system with 
spacing of more than 120\ Hz, the VFT equipment should have the following 
characteristics:
.LP
	1)
	VFT systems for wideband 50\(hybaud channels should be
homogeneous systems using frequency modulation only;
.LP
	2)
	equipment in conformity with Recommendation\ R.37 is
recommended for this purpose.
.bp
.sp 2P
.LP
\fBRecommendations\ R.36\ to\ R.38 | \fR 
.RT
.sp 2P
.ce 1000
\fBREPORT\ ON\ \fR \fBVOICE\(hyFREQUENCY\ TELEGRAPH\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ 36\ to\ R.38^B''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ 36\ to\ R.38^B	%'
.ce 0
.sp 1P
.ce 1000
\fBCHANNELS\fR \fB\ FOR\ USE\ ABOVE\ 50\ BAUDS\fR 
.ce 0
.sp 1P
.ce 1000
\fI(Common introductory report on Recommendations R.36,\fR \fIR.37, R.38 |  
and R.38 | )\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964; amended at Mar del Plata, 1968, and Geneva, 1980)\fR 
.ce 0
.sp 1P
.PP
\fB1\fR The CCITT has examined the characteristics of telegraph
circuits
for use above 50\ bauds. It has been noted that modulation rates of\ 75, 100,
150, 200 and 300\ bauds are envisaged. The CCITT considers that the number of
different types of VFT channels to be provided should not fully correspond 
to such a detailed list, for two basic reasons: 
.sp 1P
.RT
.LP
	a)
	With the exception of 300\ bauds, a particular rate circuit can
be provided over a higher rate channel. In some cases a lower
rate channel might also be considered, this being the situation
where a 300\(hybaud circuit may sometimes be supported
on a nominally 200\(hybaud channel.
.LP
	b)
	The lease charges envisaged are generally such that a marginal
tariff difference may exist between circuits operated at the
next higher rate.
.PP
\fB2\fR 
The CCITT has therefore established VFT standards for nominal 100\(hy and 
200\(hybaud channels in addition to the earlier standards for channels 
for operation at nominally 50\ bauds.
.sp 9p
.RT
.PP
\fINote\fR \ \(em\ The performance of a circuit operated at a modulation
rate of
75\ bauds via one VFT channel conforming to Recommendation\ R.35 should 
be quite satisfactory. Similarly, the performance of a circuit operated 
at a modulation rate of 300\ bauds via one VFT channel conforming to Recommendation\ 
R.38 |  may be satisfactory. However when a circuit consists of two or 
more channels in 
tandem, the use of a regenerative repeater may be required. To judge this,   
.LP
it is advisable to conduct distortion measurements on the end\(hyto\(hyend 
circuit 
concerned and also on the individual VFT channels employed. In general, 
it is recommended that circuits operated at a particular modulation rate 
should not be routed over nominally lower rate VFT channels, whenever this 
can be 
avoided.
.PP
\fB3\fR 
Very different possibilities for using these channels may   be envisaged:
.sp 9p
.RT
.LP
	\(em
	start\(hystop transmission or synchronous transmission;
.LP
	\(em
	tandem operation of several channels;
.LP
	\(em
	use of point\(hyto\(hypoint circuits, circuits with broadcast or
switched circuits;
.LP
	\(em
	integration into the world network;
.LP
	\(em
	data transmission.
.PP
\fB4\fR 
Signal regeneration devices do not normally form an integral   part
of a VFT channel, as their presence reduces the flexibility to assign a 
channel for a different use. 
.sp 9p
.RT
.PP
\fB5\fR 
With regard to channels for 200\ bauds, it has been agreed that the spacing 
for such channels should normally be 480\ Hz because of the 
.sp 9p
.RT
.LP
advantages of 480\ Hz spacing compared with 360\(hyHz spacing with regard to
distortion and the cost of equipment. But when the advantage of having a
greater number of telegraph channels on the same bearer circuit is considered 
essential by the Administration (e.g.\ on long submarine cables employing 
narrow band 3\(hykHz telephone channeling equipment), the use of 360\(hyHz 
spacing between 200\(hybaud telegraph channels may be justified. 
.PP
\fB6\fR 
For the above reasons, Recommendations\ R.36, R.37, R.38 |  and R.38 |  
have been adopted. 
.sp 9p
.RT
.PP
\fB7\fR 
Recommendation R.36 applies to heterogeneous systems and
Recommendations\ R.37, R.38 |  and\ R.38 |  apply to homogeneous systems.
.sp 9p
.RT
.PP
\fB8\fR 
For the homogeneous systems referred to by
Recommendations\ R.37,
R.38 |  and\ R.38 | , only frequency modulation is recommended.
.bp
.sp 9p
.RT
.LP
.ce
\fBH.T. [T3.35]\fR 
.ce
\fBComparative table of values for the degree of tolerable
.ce
distorsion\fR 
.ce
\fBon telegraph channels with various modulation rates\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(78p) | cw(30p) sw(30p) sw(30p) sw(30p) sw(30p) , ^  | c s s s s 
^  | c | c | c | c | c.
Reception condition	 {
Inherent isochronous distorsion (%) 
of different types of VFT
channels
 }
	Recommendation	R.35  (50 bauds  120 Hz)	R.35 | is  (50 bauds  240 Hz)	R.37  (100 bauds  240 Hz)	R.38A  (200 bauds  480 Hz)	R.38B  (200 bauds  360 Hz)
_
.T&
lw(78p) | cw(30p) | lw(30p) | cw(30p) | cw(30p) | cw(30p) .
 {
For the normal reception level
 }	\ 5		\ 5	\ 5	\ 6
_
.T&
lw(78p) | cw(30p) | lw(30p) | cw(30p) | cw(30p) | cw(30p) .
 {
In the case of slow level variation of +8,7 dB to \(em17,4\ dB with respect to
the normal reception level
 }	\ 7		\ 7	\ 7	\ 7
_
.T&
lw(78p) | cw(30p) | lw(30p) | cw(30p) | cw(30p) | cw(30p) .
 {
In the presence of interference by a single sinewave frequency equal to
either of two characteristic frequencies with a level of 20 dB below the
signal level of the test channel
 }	12		12	10	15
_
.T&
lw(78p) | cw(30p) | lw(30p) | cw(30p) | cw(30p) | cw(30p) .
 {
With introduction of a frequency drift (\(*D\fIf\fR
Hz) of the
signals:
 }					
.T&
lw(78p) | cw(30p) | lw(30p) | cw(30p) | cw(30p) | cw(30p) .
 {
a)
for a drift \(= |  Hz:
Equipment without crystal control
Equipment with crystal control but without compension for frequency drift
 }	(5 + 2.5 \(*D\fIf\fR )		(5 + 1.3 \(*D\fIf\fR )	(5 + 0.7 \(*D\fIf\fR )	 {
(6 + 1.2 \(*D\fIf\fR
) 
Equipment with crystal control and
compensation for frequency drift 
 }
.T&
cw(78p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
\ 7		\ 7			
.T&
lw(78p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) | cw(30p) .
 {
b)
for a drift \(= | 0 Hz:
Equipment with crystal control and
compensation for frequency drift 
 }	13		10		
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLE R.36 to 38 (R) [T3.35], p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
\fBRecommendation\ R.36\fR 
.RT
.sp 2P
.ce 1000
\fBCOEXISTENCE\ OF\ 50\(hyBAUD/120\(hyHz\ CHANNELS,\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.36''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.36	%'
.ce 0
.ce 1000
\fB100\(hyBAUD/240\(hyHz\ CHANNELS,\ 200\(hyBAUD/360\(hyHz\ OR\ 480\(hyHz\ 
CHANNELS\fR 
.ce 0
.sp 1P
.ce 1000
\fBON\ THE\ SAME\ \fR \fBVOICE\(hyFREQUENCY\ TELEGRAPH\ SYSTEM\fR 
.ce 0
.sp 1P
.ce 1000
\fI(New Delhi, 1960; amended at Geneva, 1964 and 1980)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.LP
\fB1\fR 	\fBCommon views\fR 
.sp 1P
.RT
.PP
1.1
Channels with higher modulation rates (100 or 200\ bauds) must be capable 
of being inserted in systems of amplitude\(hymodulated 50\(hybaud/120\(hyHz 
channels conforming to Recommendations concerning them respectively as 
well as in systems of frequency\(hymodulated 50\(hybaud/120\(hyHz channels 
(conforming to 
Recommendation\ R.35). However, it is preferable that these high\(hyspeed 
channels should, as far as possible, be placed in a frequency\(hy 
modulated\ system
(conforming to Recommendation\ R.35). However, 200\(hybaud/360\(hyHz channels 
can be set up only on systems established on bearer circuits having a spacing 
of 
3\ kHz.
.bp
.sp 9p
.RT
.LP
.PP
1.2
If there are 50\(hybaud channels on a mixed system, the distortion
limits for the 50\(hybaud channels on homogeneous 50\(hybaud channel systems 
will 
have to be respected; hence, 100\(hybaud and 200\(hybaud channel equipment 
will have to be designed to this end. If this is not possible, the power 
levels on the 
100\(hybaud and 200\(hybaud channels will have to be reduced.
.PP
1.3
The 100\(hy and 200\(hybaud channels should have performances
comparable
to those that could be obtained in a homogeneous system, as specified in
Recommendations\ R.37, R.38 | , R.38 | , provided that the condition indicated
under \(sc\ 1.2\ above is respected. They should, in particular, satisfy 
\(sc\ 13a) 
of Recommendations\ R.37, R.38 | , or R.38 |  respectively.
.PP
1.4
The mean power transmitted to line at a point of zero relative
level
is normally dependent on the transmission characteristics of the bearer 
circuit as follows: 
.LP
	a)
	50\ \(*mW total for FMVFT aggregates carried on circuits
complying with the limits specified in Annex\ A to Recommendation\ R.35;
.LP
	b)
	135\ \(*mW total for other circuits and for AMVFT.
.LP
.PP
The mean normal power for each channel should not exceed the
values specified in Table\ 1/R.36, for cases\ a) and\ b) above.
.LP
.ce
\fBH.T. [T1.36]\fR 
.ce
TABLE\ 1/R.36
.ce
\fBVFT channel power levels\fR 
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(36p) sw(36p) | cw(48p) | cw(36p) sw(36p) sw(36p) , c | c ^  | | c | c | c.
 {
VFT channel power level (\(*mW)
 }	Relevant Recommendation	VFT channel characteristics
Bearer  case a)	Bearer  case b)	Modulation rate (bauds)	Bandwidth  (Hz)	Type of modulation
_
.T&
cw(36p) | cw(36p) | lw(48p) | cw(36p) | cw(36p) | cw(36p) .
\(em	 {
\ 9\fB.6 | fR\(ua\fBa\fR\(ua\fB)\fR
 }	R.31	\ 50	120	AM
.T&
cw(36p) | cw(36p) | lw(48p) | cw(36p) | cw(36p) | cw(36p) .
 {
2.0\fB | fR\(ua\fBa\fR\(ua\fB)\fR
 }	 {
\ 5.6\fB | fR\(ua\fBa\fR\(ua\fB)\fR
 }	R.35	\ 50	120	FM
.T&
cw(36p) | cw(36p) | lw(48p) | cw(36p) | cw(36p) | cw(36p) .
4.0 | ua\d\u)\d	10.8 | ua\d\u)\d	R.37	100	240	FM
.T&
cw(36p) | cw(36p) | lw(48p) | cw(36p) | cw(36p) | cw(36p) .
\(em	19.2 | ua\d\u)\d	R.38B	200	360	FM
.T&
cw(36p) | cw(36p) | lw(48p) | cw(36p) | cw(36p) | cw(36p) .
8.0 | ua\d\u)\d	21.6 | ua\d\u)\d	R.38A	200	480	 {
FM
\ua\d\u)\d
Provided that the condition mentioned under \(sc 1.2 is respected.
 }
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLE 1/R.36 (R) [T1.36], p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 2P
.LP
.sp 2
\fB2\fR 	\fBCombined use of channels with 240\(hyHz spacing and channels\fR 
\fBwith 120\(hyHz spacing\fR 
.sp 1P
.RT
.PP
For the numbering of channels that has been adopted in the
international services see Recommendation\ R.70 | fIbis\fR .
.FE
2.1
Channels with 240\(hyHz spacing should be installed in the following preferred 
order: 12 (if possible), 11, 10, 9, 8, 7,\ . |  |  The channel 
numbers
are in accordance with Recommendation\ R.37
(100\(hybaud channels with 240\(hyHz spacing).
.sp 9p
.RT
.LP
.sp 2P
.LP
\fB3\fR 	\fBCombined use of 200\(hybaud channels with 360\(hyHz spacing\fR 
\fBand channels with 120\(hyHz or 240\(hyHz spacing\fR 
.sp 1P
.RT
.PP
3.1
The characteristics of these channels with high modulation rates are defined 
in Recommendations\ R.37 on 100\(hybaud channels with 240\(hyHz spacing 
and\ R.38 |  on 200\(hybaud channels with 360\(hyHz spacing.
.sp 9p
.RT
.PP
3.2
The 200\(hybaud/360\(hyHz channels should be installed in the following
preferred order: 5, 4, 6, 3, 2,\ 1 instead of the corresponding 50\(hybaud
channels. The channel numbers
are in accordance with
Recommendation\ R.38 | .
.bp
.LP
.PP
3.3
In combined systems using channels with three different
smodulation
rates, the order indicated in \(sc\ 3.2\ above should be used in preference 
to that indicated in \(sc\ 2.1\ above. 
.sp 2P
.LP
\fB4\fR 	\fBCombined use of 200\(hybaud channels with 480\(hyHz spacing\fR 
\fBand channels with 120\(hyHz or 240\(hyHz spacing\fR 
.sp 1P
.RT
.PP
4.1
For a combination of channels with 240\(hyHz spacing and channels
with 480\(hyHz spacing, the channels with 480\(hyHz spacing should be installed 
in 
the following preferential order: 4, 3, 5, 2,\ 6
.
.sp 9p
.RT
.PP
4.2
For a combination of channels with 120\(hyHz spacing and channels
with 480\(hyHz spacing, the order indicated in \(sc\ 4.1\ above is applicable.
.PP
\fINote\fR \ \(em\ In cooperation with a system using 6\(hychannel group
modulation, the preferred order would be: 4, 3, 6 (if possible),\ 1
.
.PP
4.3
In combined systems using channels with three different
modulation
rates, the order indicated in \(sc\ 4.1\ above should be used in preference 
to that indicated in \(sc\ 2.1\ above. 
\v'6p'
.sp 2P
.LP
\fBRecommendation\ R.37\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBSTANDARDIZATION\ OF\ \fR \fBFMVFT\ SYSTEMS\fR \fB\ FOR |
A\ MODULATION\ RATE\ OF\ 100\ BAUDS\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.37''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.37	%'
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964; amended at Mar del Plata, 1968, Geneva,\fR  |
\fI1972, 1976, 1980,\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIMalaga\(hyTorremolinos, 1984 and at Melbourne, 1988)\fR 
.ce 0
.sp 1P
.PP
\fINote\fR \ \(em\ In this Recommendation frequency\(hymodulated
voice\(hyfrequency telegraph (FMVFT) equipment with and without crystal control
are distinguished. In order to improve the quality of transmission and to
minimize maintenance costs, the application of equipment with crystal control 
is recommended. 
.sp 1P
.RT
.LP
.PP
\fB1\fR 
The nominal modulation rate is standardized at 100\ bauds.
.sp 9p
.RT
.PP
\fB2\fR 
The nominal mean frequencies are 480\ +\ (\fIn\fR \ \(em\ 1) 240\ Hz, \fIn\fR 
being
the channel position number. The mean frequency is defined as half the 
sum of the characteristic frequencies corresponding to the start polarity 
and stop 
polarity. For the numbering of channels that has been adopted in the
international service see 
Recommendation\ R.70 | fIbis\fR .
.sp 9p
.RT
.PP
\fB3\fR 
The mean frequencies at the sending end should not deviate from their nominal 
value by more than: 
.sp 9p
.RT
.LP
	a)
	for equipment without crystal control 3\ Hz;
.LP
	b)
	for equipment with crystal control 0.5\ Hz
.
.PP
\fB4\fR 
The difference between the two characteristic frequencies in
the same channel is fixed at 120\ Hz.
.sp 9p
.RT
.PP
\fB5\fR 
The maximum tolerance on this difference should be
\(+- | \ Hz.
.sp 9p
.RT
.PP
\fB6\fR 
The unbalance due to the modulation process
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR  | 
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e,
should not exceed 2%,
.sp 9p
.RT
.LP
where
.LP
	\fIF\fR  | 
\fI
\dA\u\fR and \fIF\fR  | 
\fI
\dZ\u\fR 	are
the two
characteristic frequencies measured over a period of 10\ s;
.LP
	\fIF\fR  | 
\d0\u
	is the mean static frequency
measured 
$$1o\fIF\fR  | 
\fI
\dA\u\fR + \fIF\fR  | 
\dZ\u\fR $$1u2
$$1e;
.LP
	\fIF\fR\d\fIl\fR\u	is the mean dynamic frequency measured with
1:1\ rectangular signals during 10\ s.
.bp
.PP
Measurement should be made applying to the input of the
transmitter\ 1:1 rectangular signals with the build\(hyup and hangover 
time below 1\ \(*ms and with the unbalance below 0.1%. In the event that 
in service the 
transmitter is controlled by an electro\(hymechanical relay (with a certain
transit time), the measurement should also be made with that type of relay
inserted between the 1:1\ signal generator and the input to the transmitter.
Both forms of measurement need not necessarily be included in the maintenance 
procedure but should be included in laboratory type tests. 
.PP
\fINote\fR \ \(em\ To determine the unbalance due to the modulation process by
the method indicated above, it is necessary to measure the
frequencies\ \fIF\fR  | 
\fI
\dA\u\fR , \fIF\fR  | 
\fI
\dZ\u\fR and \fIF\fR\d\fIl\fR\u
and
to calculate the mean frequency\ \fIF\fR  | 
\d0\u
and the
unbalance
\v'6p'
.RT
.sp 1P
.ce 1000
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
.ce 0
.sp 1P
.LP
.sp 1
.PP
A more rapid method for checking whether or not the unbalance is
less than the limit fixed is to measure:
.LP
	\(em
	the mean dynamic frequency \fIF\fR\d\fIl\fR\uwith 1:1\ signals during
10\ s;
.LP
	\(em
	the mean dynamic frequency \fIF\fR\d\fIm\fR\uwith 2:2\ signals during
10\ s;
\v'6p'
.sp 1P
.ce 1000
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em
\fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em \fIF\fR  | 
\fI
\dZ\u\fR $$1e =
4 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dm\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
.ce 0
.sp 1P
.LP
.sp 1
or to subtract:
\v'6p'
.sp 1P
.ce 1000
| fIF
\dl\u\fR \(em \fIF
\dm\u\fR | = 
$$Bo1
} over { 
$$Be (\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR ) | (*d \( =
$$Bo1
} over { 
$$Be (\fIF
\dA\u\fR \(em \fIF
\dZ\u\fR ) | (*d \(= 0.9 Hz.
.ce 0
.sp 1P
.PP
.sp 1
The absolute value of the difference between the two frequencies
measured, \fIF\fR\d\fIl\fR\uand \fIF\fR\d\fIm\fR\u, must be less than 0.9\ Hz.
.LP
.PP
\fB7\fR 
The total average power transmitted to the telephone\(hytype
circuit
is normally dependent on the transmission characteristics of the circuit as
follows:
.sp 9p
.RT
.LP
	a)
	 For circuits with characteristics not exceeding the limits (nominal values) 
given in Annex\ A to Recommendation\ R.35, the mean power per channel 
at a point of relative zero level should not be more than 4.0\ \(*mW
(\(em24.0\ dBm0). The pilot channel, where employed, should have a
level of not more than 2.0\ \(*mW (\(em27.0\ dBm0);
.LP
	b)
	for other circuits, the mean power per channel at a point of
relative zero level should not be more than 10.8\ \(*mW
(\(em19.7\ dBm0). The pilot channel, where employed,
should have a level of not more than 5.4\ \(*mW
(\(em22.7\ dBm0).
.PP
\fB8\fR 
In service, the levels of signals corresponding to continuous
condition\ Z
and continuous condition\ A should not differ by more than 1.7\ dB in
the same channel. Both of these levels must lie between \(+- | .7\ dB with 
reference to the level in \(sc\ 7\ above. 
.sp 9p
.RT
.LP
.PP
\fB9\fR 
The frequency for the transmitted condition corresponding to the condition\ 
A is the higher of the two characteristic frequencies and that 
corresponding to the condition\ Z is the lower.
.sp 9p
.RT
.PP
\fB10\fR In the absence of a channel\(hymodulator control telegraph current, 
a frequency shall be transmitted that shall be within \(+- | 0\ Hz of the 
frequency normally transmitted for the condition\ A. It is not necessary 
for this 
transmission to take place immediately after the control current has been cut.
.sp 9p
.RT
.PP
\fB11\fR The frequency spectrum of the emitted signal, when transmitting 
1:1\ reversals (Definition\ 31.401, 
Recommendation\ R.140)
at the modulation rate of 2\ \fIf\fR\d\fIp\fR\u(
\fIf\fR\d\fIp\fR\u\ =\ frequency
of modulation), should be in accordance with the limits specified in
Figure\ 1/R.37, which shows the levels of the spectra of different components
with respect to the amplitude of the non\(hymodulated carrier as ordinates 
and the frequencies as abscissae. 
.sp 9p
.RT
.PP
\fB12\fR The receiving equipment should operate satisfactorily when the 
receiving level falls to 17.4\ dB below the nominal level. The receiving 
equipment should have been restored to condition\ A when the receiving level
has fallen to 23.5\ dB below the nominal level. The alarm\(hycontrol level 
is left to the choice of each Administration. 
.bp
.sp 9p
.RT
.PP
\fB13\fR 
On delivery by the manufacturer of 100\(hybaud FMVFT equipment, the following 
values must not be exceeded for the degree of distortion on a 
telegraph channel. These values correspond to closed circuit measurements, 
made with the audio\(hyfrequency line terminals of the sending and receiving 
equipments connected together through an artificial line. Before the series 
of 
measurements taken in accordance with Recommendation\ R.51, the levels are
adjusted to their normal values, the mean frequencies are checked to see
whether they are within:
.sp 9p
.RT
.LP
	1)
	for equipment without crystal control \(+- | \ Hz;
.LP
	2)
	for equipment with crystal control \(+- | .1\ Hz
,
.LP
.rs
.sp 36P
.ad r
\fBFIGURE 1/R.37, p.\fR 
.sp 1P
.RT
.ad b
.RT
.LP
of their nominal value (see \(sc\ 3 above) and the difference between the two
characteristic frequencies is within the permitted tolerance of less than
4\ Hz (see \(sc\ 5 above). Bias distortion is eliminated by adjustment in the
channel receivers. The other channels of the system are modulated with
unrelated signals when the effect of interchannel interference is to be
included in the measurement. These \*Qunrelated signals\*U can conveniently be
1:1\ signals from different generators at approximately 100\ bauds but not
synchronous to each other or to the signal on the channel under test.
.bp
.LP
	a)
	The transmission levels being normal, the artificial line
introducing no frequency drift, but the measured channel being subject to
fortuitous distortion due to interchannel interference: 5%\ for the degree of
inherent isochronous distortion.
.LP
	b)
	The level being maintained constant, but at a value different
from
the normal level, for all constant levels between 8.7\ dB above the normal
reception level and 17.4\ dB below the normal reception level, the other
conditions being the original measurement conditions: 7%\ for the degree of
inherent isochronous distortion.
.LP
	c)
	In the presence of interference by a single sine\(hywave frequency
equal first to one and then to the other characteristic frequency, with 
a level of 20\ dB below the signal level, the other conditions for the 
start of 
measurements being maintained: 12%\ for the degree of inherent isochronous
distortion (i.e.\ total distortion including the increase due to the interfering 
frequency, not distortion due to the interfering frequency alone). 
\v'1P'
.sp 2P
.LP
\fBRecommendation\ R.38 | \fR 
.RT
.sp 2P
.ce 1000
\fBSTANDARDIZATION\ OF\ \fR \fBFMVFT\ SYSTEM\fR \fB\ FOR\ A\ MODULATION\ 
RATE\ OF\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.38^A''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.38^A	%'
.ce 0
.sp 1P
.ce 1000
\fB200\ BAUDS\ WITH\ CHANNELS\ SPACED\ AT\ 480\ Hz\fR 
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964; amended at Mar del Plata, 1968,\fR  |
\fIGeneva, 1972, 1976, 1980,\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIMalaga\(hyTorremolinos, 1984 and at Melbourne, 1988)\fR 
.ce 0
.sp 1P
.PP
\fINote\ 1\fR \ \(em\ This is the standardized system for operation at
200\ bauds.
.sp 1P
.RT
.PP
\fINote\ 2\fR \ \(em\ In this Recommendation frequency\(hymodulated
voice\(hyfrequency telegraph (FMVFT) equipment with and without crystal control
are distinguished. In order to improve the quality of transmission and to
minimize maintenance costs, the application of equipment with crystal control 
is recommended. 
.LP
.PP
\fB1\fR 
The nominal modulation rate is fixed at 200\ bauds.
.sp 9p
.RT
.PP
\fB2\fR 
The nominal mean frequencies are 600\ +\ (\fIn\fR \ \(em\ 1) 480\ Hz, \fIn\fR 
being
the channel position number. The mean frequency is defined as half the 
sum of the characteristic frequencies corresponding to conditions A and 
Z. 
For the numbering of channels that has been adopted in the international
service see Recommendation\ R.70 | fIbis\fR .
.sp 9p
.RT
.PP
\fB3\fR 
The mean frequencies at the sending end should not deviate from their nominal 
value by more than: 
.sp 9p
.RT
.LP
	a)
	for equipment without crystal control 4\ Hz;
.LP
	b)
	for equipment with crystal control 0.8\ Hz
.
.PP
\fB4\fR 
The difference between the two characteristic frequencies in the same channel 
is fixed at 240\ Hz. 
.sp 9p
.RT
.PP
\fB5\fR 
The maximum tolerance on this difference should be
\(+- | \ Hz.
.sp 9p
.RT
.PP
\fB6\fR 
The unbalance due to the modulation process
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
should not exceed 2%,
.sp 9p
.RT
.LP
where
.LP
	\fIF\fR  | 
\fI
\dA\u\fR and \fIF\fR  | 
\fI
\dZ\u\fR 	are the two
characteristic frequencies
measured over a period of 10\ s;
.LP
	\fIF\fR  | 
\d0\u
	is the mean static frequency measured
$$1o\fIF\fR  | 
\fI
\dA\u\fR + \fIF\fR  | 
\fI
\dZ\u\fR $$1u2
$$1e;
.LP
	\fIF\fR\d\fIl\fR\u	is the mean dynamic frequency measured with
1:1\ rectangular signals during 10\ signals.
.bp
.PP
Measurement should be made applying to the input of the transmitter 1:1\ 
rectangular signals with the build\(hyup and hangover time below 1\ \(*ms 
and 
with the unbalance below 0.1%. In the event that in service the transmitter 
is controlled by an electro\(hymechanical relay (with a certain transit 
time), the 
measurement should also be made with that type of relay inserted between the
1:1\ signal generator and the input to the transmitter. Both forms of
measurements need not necessarily be included in the maintenance procedure 
but should be included in laboratory type tests. 
.PP
\fINote\fR \ \(em\ To determine the unbalance due to the modulation process by
the method indicated above, it is necessary to measure the
frequencies\ \fIF\fR  | 
\fI
\dA\u\fR , \fIF\fR  | 
\fI
\dZ\u\fR and \fIF\fR\d\fIl\fR\uand
to
calculate the mean frequency\ \fIF\fR  | 
\d0\u
and the unbalance
\v'6p'
.RT
.sp 1P
.ce 1000
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
.ce 0
.sp 1P
.PP
.sp 1
A more rapid method for checking whether or not the unbalance is
less than the limit fixed is to measure:
.LP
	\(em
	the mean dynamic frequency \fIF\fR\d\fIl\fR\uwith 1:1\ signals during
10\ s;
.LP
	\(em
	the mean dynamic frequency \fIF\fR\d\fIm\fR\uwith 2:2\ signals during
10\ s;
\v'6p'
.LP
.sp 1P
.ce 1000
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e =
4 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dm\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
.ce 0
.sp 1P
.LP
.sp 1
or to subtract:
\v'6p'
.sp 1P
.ce 1000
| fIF
\dl\u\fR \(em \fIF
\dm\u\fR | = 
$$Bo1
} over { 
$$Be (\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR ) | (*d \( =
$$Bo1
} over { 
$$Be (\fIF
\dA\u\fR \(em \fIF
\dZ\u\fR ) | (*d \(= 1.8 Hz.
.ce 0
.sp 1P
.PP
.sp 1
The absolute value of the difference between the two frequencies measured, 
\fIF\fR\d\fIl\fR\uand \fIF\fR\d\fIm\fR\u, must be less than 1.8\ Hz. 
.PP
\fB7\fR The total average power transmitted to the telephone\(hytype circuit 
is normally dependent on the transmission characteristics of the circuit 
as 
follows:
.sp 9p
.RT
.LP
	a)
	For circuits with characteristics not exceeding the limits given
in Annex\ A to Recommendation\ R.35, the mean power per channel at a point of
relative zero level should not be more than 8.0\ \(*mW (\(em21.0\ dBm0). 
The pilot 
channel, where employed, should have a level of not more than 2.0\ \(*mW
(\(em27.0\ dBm0).
.LP
	b)
	For other circuits, the mean power per channel at a point of
relative zero level should not be more than 21.6\ \(*mW (\(em16.7\ dBm0). 
The pilot 
channel, where employed, should have a level of not more than 5.4\ \(*mW
(\(em22.7\ dBm0).
.PP
\fB8\fR 
In service, the levels of the signals corresponding to
continuous condition\ Z and continuous condition\ A should not differ by more
than 1.7\ dB in the same channel. Both of these levels must lie between 
\(+- | .7\ dB with reference to the level in \(sc\ 7\ above. 
.sp 9p
.RT
.PP
\fB9\fR 
The condition\ A frequency is the higher of the two
characteristic frequencies, and the condition\ Z frequency is the lower one
(see Recommendation\ V.1\ [1]).
.sp 9p
.RT
.LP
.PP
\fB10\fR In the absence of a channel\(hymodulator control telegraph current, 
a frequency shall be transmitted that shall be within \(+- | 0\ Hz of the 
frequency normally transmitted for the condition\ A. It is not necessary 
for this 
transmission to take place immediately after the control current has been cut.
.sp 9p
.RT
.PP
\fB11\fR The frequency spectrum of the emitted signal, when transmitting 
1:1\ reversals (Definition\ 31.401, Recommendation\ R.140) at the modulation 
rate of 2\ \fIf\fR\d\fIp\fR\u\ (\fIf\fR\d\fIp\fR\u\ =\ frequency of 
modulation) should be in accordance with the limits specified in Figure\ 
1/R.37, which shows the levels of the spectra of different components with 
respect to the amplitude of the non\(hymodulated carrier as ordinates and 
the frequencies as abscissae. 
.sp 9p
.RT
.PP
\fB12\fR The receiving equipment should operate satisfactorily when the 
receiving level falls to 17.4\ dB below the nominal level. The receiving 
equipment should have been restored to condition\ A when the receiving level
has fallen to 23.5\ dB below the nominal level. The alarm\(hycontrol level 
is left to the choice of each Administration. 
.bp
.sp 9p
.RT
.PP
\fB13\fR On delivery by the manufacturer of 200\(hybaud/480\(hyHz
frequency\(hymodulated voice\(hyfrequency telegraph (FMVFT) equipment, 
the following values must not be exceeded for the degree of distortion 
on a telegraph 
.sp 9p
.RT
.LP
channel. These values correspond to closed circuit measurements, made with 
the audio\(hyfrequency line terminals of the sending and receiving equipments 
connected together through an artificial line. Before the series of
measurements taken in accordance with Recommendation\ R.51, the levels are
adjusted to their normal values, the mean frequencies are checked to see
whether they are within:
.LP
	1)
	for equipment without crystal control \(+- | \ Hz;
.LP
	2)
	for equipment with crystal control \(+- | .8\ Hz,
.LP
of their nominal value (see \(sc\ 3\ above) and the
difference between the two characteristic frequencies is within the permitted 
tolerance of less than 6\ Hz (see \(sc\ 5\ above). Bias distortion is eliminated 
by adjustment in the channel receivers. The other channels of the system 
are 
modulated with unrelated signals when the effect of interchannel interference 
is to be included in the measurement. These \*Qunrelated signals\*U can 
conveniently be 1:1\ signals from different generators at approximately
200\ bauds but not synchronous to each other or to the signal on the channel
under test.
.LP
	a)
	The transmission levels being normal, the artificial line
introducing no frequency drift, but the measured channel being subject to
fortuitous distortion due to interchannel interference: 5% for the degree of
inherent isochronous distortion.
.LP
	b)
	The level being maintained constant, but at a value different
from the normal level, for all constant levels between 8.7\ dB above the 
normal reception level and 17.4\ dB below the normal reception level, the 
other 
conditions being the original measurement conditions: 7% for the degree of
inherent isochronous distortion.
.LP
	c)
	In the presence of interference by a single sine\(hywave frequency
equal first to one and then to the other characteristic frequency, with 
a level of 20\ dB below the signal level, the other conditions for the 
start of 
measurements being maintained: 10% for the degree of inherent isochronous
distortion (i.e.\ total distortion including the increase due to the interfering 
frequency, not distortion due to the interfering frequency alone). 
.LP
	d)
	By introducing a frequency drift (\(*D\fIf\fR \ Hz) of the signals during
transmission through the artificial line, \(*D\fIf\fR \ in Hz being not 
more than 10, 
and the initial conditions of the test otherwise being
preserved: (5\ +\ 0.7\ \(*D\fIf\fR \ Hz)% for the degree of inherent isochronous
distortion; the measurements shall be made after the transient effects of
changing frequency have ceased.
.LP
	e)
	Equipment with crystal control, with any climatic conditions
specified for the tested equipment, the initial condition of
the test otherwise being preserved: 8% for the degree of
inherent isochronous distortion. The bias distortion caused
by changes of climatic conditions should not be eliminated.
.PP
\fB14\fR 
Frequency drifts on modern telephone\(hytype circuits are
generally less than 2\ Hz. Hence it is not necessary to recommend frequency
drift control. For circuits on which a maximum frequency drift of not greater 
than \(+- | \ Hz cannot be guaranteed, and on which the distortion resulting 
from 
the
frequency drift is not acceptable, compensation seems necessary. Two methods
can be used:
.sp 9p
.RT
.LP
	a)
	compensation for each channel up to about 15\ Hz;
.LP
	b)
	compensation for all the channels by using a pilot. In this
case, the receiving end must be able to request and obtain a
pilot frequency. Administrations should agree among themselves
on the advisability of sending the pilot and the choice of
frequency. The frequencies 3300\ Hz or, preferably, 300\ Hz are recommended 
for this pilot, with a tolerance of: 
.LP
	1)
	for equipment without crystal control \(+- | \ Hz
.LP
	2)
	for equipment with crystal control \(+- | .2\ Hz.
.LP
	The mean power emitted at the relative zero point on this
frequency
should not exceed \(em27.0\ dBm0 or \(em22.7\ dBm0 as appropriate (see 
\(sc\ 7 and 
Tables\ 1/R.35 and\ 2/R.35 in Recommendation\ R.35, which are also applicable 
to equipment to this Recommendation). 
.bp
.PP
\fB15\fR The number of significant conditions of the modulation is fixed 
at two; this number may be increased, if necessary, by agreement between 
the 
Administrations concerned.
.sp 9p
.RT
.LP
.sp 2P
.LP
	\fBReference\fR 
.sp 1P
.RT
.LP
[1]
	 CCITT Recommendation \fIEquivalence between binary notation symbols and\fR 
the significant conditions of a two\(hycondition code\fR , Rec.\ V.1. 
.LP
.sp 2P
.LP
\fBRecommendation\ R.38 | \fR 
.RT
.sp 2P
.ce 1000
\fBSTANDARDIZATION\ OF\ \fR \fBFMVFT\ SYSTEMS\fR \fB\ FOR\ A\ MODULATION\ 
RATE | 
OF\ 200\ BAUDS\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.38^B''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.38^B	%'
.ce 0
.ce 1000
\fBWITH\ CHANNELS\ SPACED\ AT\ 360\ Hz\fR 
.ce 0
.ce 1000
\fBUSABLE\ ON\ LONG\ INTERCONTINENTAL\ BEARER\ CIRCUITS\fR 
.ce 0
.sp 1P
.ce 1000
\fBGENERALLY\ USED\ WITH\ A\ 3\(hykHz\ SPACING\fR 
.ce 0
.sp 1P
.ce 1000
\fI(Geneva, 1964; amended at Geneva, 1972, 1976, 1980 and\fR \fIMalaga\(hyTorremolinos, 
1984)\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.PP
\fB1\fR 
Frequency\(hymodulated voice\(hyfrequency telegraph (FMVFT) systems, with 
a spacing of 360\ Hz between the mean frequencies, can accommodate seven 
channels. In the case of telephone bearer channels with 4\(hykHz spacing, 
channel position\ 8 can be used. 
.sp 1P
.RT
.LP
.PP
\fB2\fR 
The nominal modulation rate is fixed at 200\ bauds.
.sp 9p
.RT
.PP
\fB3\fR 
The nominal mean frequencies are 540\ +\ (\fIn\fR \ \(em\ 1) 360\ Hz,
\fIn\fR \ being
the channel position number. The mean frequency is defined as half the 
sum of the characteristic frequencies corresponding to the conditions\ 
A and\ Z. 
For the numbering of channels that has been adopted in the international
service see Recommendation\ R.70 | fIbis\fR .
.sp 9p
.RT
.PP
\fB4\fR 
The mean frequencies at the sending end must not deviate by more than\ 
\(+- | \ Hz from their nominal value. 
.sp 9p
.RT
.PP
\fB5\fR 
The difference between the two characteristic frequencies in the same channel 
is fixed at\ 180\ Hz. 
.sp 9p
.RT
.PP
\fB6\fR 
The maximum tolerance on this difference should
be\ \(+- | \ Hz.
.sp 9p
.RT
.PP
\fB7\fR 
The unbalance due to the modulation process
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
should not exceed\ 2%,
.sp 9p
.RT
.LP
where
.LP
	\fIF\fR  | 
\fI
\dA\u\fR and \fIF\fR  | 
\fI
\dZ\u\fR 	are the two
characteristic frequencies measured over a period of 10\ s;
.LP
	\fIF\fR  | 
\d0\u
	is the mean static frequency measured
$$1o\fIF\fR  | 
\fI
\dA\u\fR + \fIF\fR  | 
\fI
\dZ\u\fR $$1u2
$$1e;
.LP
	\fIF\fR\d\fIl\fR\u	is the mean dynamic frequency measured with 1:1
rectangular signals during 10\ s.
.PP
Measurements should be made applying to the input of the
transmitter 1:1 rectangular signals with the build\(hyup and hangover time
below\ 1\ \(*ms and with the unbalance below\ 0.1%. In the event that in
service the transmitter is controlled by an electro\(hymechanical relay (with a
certain transit time), the measurement should also be made with that type of
relay inserted between the 1:1\ signal generator and the input to the
transmitter. Both forms of measurements need not necessarily be included 
in the maintenance procedure but should be included in laboratory type 
tests.
.PP
\fINote\fR \ \(em\ To determine the unbalance due to the modulation process by
the method indicated above, it is necessary to measure the
frequencies\ \fIF\fR  | 
\fI
\dA\u\fR , \fIF\fR  | 
\fI
\dZ\u\fR and \fIF\fR\d\fIl\fR\uand
to calculate the mean frequency\ \fIF\fR  | 
\d0\u
and the
unbalance
\v'6p'
.RT
.LP
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e.
.bp
.sp 1P
.ce 1000
.ce 0
.sp 1P
.PP
A more rapid method for checking whether or not the unbalance is
less than the limit fixed is to measure:
.LP
	\(em
	the mean dynamic frequency \fIF\fR\d\fIl\fR\uwith 1:1\ signals during
10\ s;
.LP
	\(em
	the mean dynamic frequency \fIF\fR\d\fIm\fR\uwith 2:2\ signals during
10\ s;
\v'6p'
.LP
.sp 1P
.ce 1000
\(*d = 2 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dl\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR 
\(em \fIF\fR  | 
\fI
\dZ\u\fR $$1e =
4 
$$1 | fIF\fR  | 
\d0\u
\(em \fIF
\dm\u\fR |
$$1u\fIF\fR  | 
\fI
\dA\u\fR \(em
\fIF\fR  | 
\fI
\dZ\u\fR $$1e
.ce 0
.sp 1P
.LP
.sp 1
or to subtract:
\v'6p'
.sp 1P
.ce 1000
| fIF
\dl\u\fR \(em \fIF
\dm\u\fR | = 
$$Bo1
} over { 
$$Be (\fIF\fR  | 
\fI
\dA\u\fR 
\(em
\fIF\fR  | 
\fI
\dZ\u\fR ) | (*d \( =
$$Bo1
} over { 
$$Be (\fIF
\dA\u\fR \(em \fIF
\dZ\u\fR ) | (*d \(= 1.3 Hz.
.ce 0
.sp 1P
.PP
.sp 1
The absolute value of the difference between the two frequencies measured,\ 
\fIF\fR\d\fIl\fR\uand\ \fIF\fR\d\fIm\fR\u, must be less than\ 1.3\ Hz. 
.PP
\fB8\fR 
The mean power per channel at relative zero level should not be more than 
19.2\ microwatts. 
.sp 9p
.RT
.PP
\fB9\fR 
In service, the levels of the signals corresponding to
continuous
condition\ Z and continuous condition\ A should not differ by more
than 1.7\ dB in the same channel. Both of these levels must lie between\ 
\(+- | .7\ dB with reference to the level in \(sc\ 8 above. 
.sp 9p
.RT
.LP
.PP
\fB10\fR The condition\ A frequency is the higher of the two
characteristic
frequencies, and the condition\ Z is the lower one (see
Recommendation\ V.1\ [1]).
.sp 9p
.RT
.PP
\fB11\fR In the absence of a channel\(hymodulator control telegraph current, 
a frequency shall be transmitted that shall be within \(+- | 0\ Hz of the 
frequency normally transmitted for the condition\ A. It is not necessary 
for this 
transmission to take place immediately after the control current has been
cut.
.sp 9p
.RT
.PP
\fB12\fR The receiving equipment should operate satisfactorily when the 
receiving level falls to 17.4\ dB below the nominal level. The receiving 
equipment should have been restored to condition\ A when the receiving
level has fallen to 23.5\ dB below the nominal level. The alarm\(hycontrol 
level is left to the choice of each Administration. 
.sp 9p
.RT
.PP
\fB13\fR On delivery by the manufacturer of 200\(hybaud/360\(hyHz
FMVFT\ equipment,
the following values must not be exceeded for the degree of distortion on a
telegraph channel. These values correspond to closed circuit measurements, 
made with the audio\(hyfrequency line terminals of the sending and receiving 
equipments connected together through an artificial line. Before the series 
of 
measurements taken in accordance with 
Recommendation\ R.51, the levels are
adjusted to their normal values, the mean frequencies are checked to see
whether they are within \(+- | \ Hz of their nominal value (see \(sc\ 4\ 
above) and the difference between the two characteristic frequencies is 
within the permitted tolerance of less than 4\ Hz (see \(sc\ 6 above). 
Bias distortion is eliminated by adjustment in the channel receivers. The 
other channels of the system are 
modulated with unrelated signals when the effect of interchannel interference 
is to be included in the measurement. These \*Qunrelated signals\*U can 
conveniently be 1:1\ signals from different generators at approximately
200\ bauds but not synchronous to each other or to the signal on the channel
under test.
.sp 9p
.RT
.LP
	a)
	The transmission levels being normal, the artificial line
introducing no frequency drift, but the measured channel being subject to
fortuitous distortion due to interchannel interference:\ 6% for the degree of
inherent isochronous distortion.
.LP
	b)
	The level being maintained constant, but at a value different
from the normal level, for all constant levels between 8.7\ dB above the 
normal reception level and 17.4\ dB below the normal reception level, the 
other 
conditions being the original measurement conditions: 8% for the degree of
inherent isochronous distortion.
.LP
	c)
	In the presence of interference by a single sine\(hywave frequency
equal first to one and then to the other characteristic frequency, with 
a level of 20\ dB\ below the signal level, the other conditions for the 
start of 
measurements being maintained: 15% for the degree of inherent isochronous
distortion (i.e.\ total distortion including the increase due to the interfering 
frequency, not distortion due to the interfering frequency alone). 
.LP
	d)
	By introducing a frequency drift (\(*D\fIf\fR \ Hz) of the signals during
transmission through the artificial line, \(*D\fIf\fR \ being not more than\ 
10; and the initial conditions of the test otherwise being preserved: (6\ 
+\ 1.2\ \(*D\fIf\fR \ Hz)% 
for the degree of inherent isochronous distortion; the measurements shall be
made after the transient effects of changing frequency have ceased.
.bp
.PP
\fB14\fR Frequency drifts on modern telephone\(hytype circuits are generally 
less than 2\ Hz. Hence, it is not necessary to recommend frequency drift 
control. For circuits on which a maximum frequency drift of not greater
than \(+- | \ Hz cannot be guaranteed, and on which the distortion resulting
from the frequency drift is not acceptable, compensation seems necessary. 
Two methods can be used: 
.sp 9p
.RT
.LP
	\(em
	compensation for each channel up to about 15\ Hz;
.LP
	\(em
	compensation for all the channels by using a pilot. In this
case, the receiving end must be able to request and obtain
a pilot frequency. Administrations should agree among  
.LP
themselves on the advisability of sending the pilot and the
choice of frequency. The frequency 300\ Hz is recommended,
with a tolerance of\ \(+- | \ Hz. The mean power emitted at the
relative zero point on this frequency should not exceed that
recommended for a telegraph channel in the case of a 24\(hychannel
group, i.e.\ \(em22.5\ dBm0.
.PP
\fB15\fR The number of significant conditions of the modulation is fixed 
at two; this number may be increased, if necessary, by agreement between 
the 
Administrations concerned.
.sp 9p
.RT
.sp 2P
.LP
	\fBReference\fR 
.sp 1P
.RT
.LP
[1]
	 CCITT Recommendation \fIEquivalence between binary notation symbols and\fR 
\fIthe significant conditions of a two\(hycondition code\fR , Vol.\ VIII, 
Fascicle\ VIII.1, Rec.\ V.1.
\v'6p'
.sp 2P
.LP
\fBRecommendation\ R.39\fR 
.RT
.sp 2P
.sp 1P
.ce 1000
\fBVOICE\(hyFREQUENCY\ TELEGRAPHY\ ON\ RADIO\ CIRCUITS\fR 
.EF '%	Fascicle\ VII.1\ \(em\ Rec.\ R.39''
.OF '''Fascicle\ VII.1\ \(em\ Rec.\ R.39	%'
.ce 0
.sp 1P
.ce 1000
\fI(former CCIT Recommendation B.49, Geneva, 1956; amended at\fR 
\fIGeneva, 1964,\fR 
.sp 9p
.RT
.ce 0
.sp 1P
.ce 1000
\fIMar del Plata, 1968, Geneva, 1976 and Melbourne, 1988)\fR 
.ce 0
.sp 1P
.PP
It is necessary to distinguish between the case in which the
radio
frequency used is below approximately 30\ MHz, and the case in which the 
radio frequency used is greater than approximately 30\ MHz. 
.sp 1P
.RT
.sp 2P
.LP
\fB1\fR 	\fBRadio circuits the frequency of which is below approximately\fR 
\fB30 MHz\fR 
.sp 1P
.RT
.LP
.PP
1.1
In the case of radio circuits whose frequency is less than
approximately 30\ MHz, it appears that the use of amplitude\(hymodulated
voice\(hyfrequency telegraph systems, as defined by Recommendation\ R.31, 
cannot be 
recommended. In such a case, the nature of the telephone\(hytype circuits
available for telegraph operation may vary widely according to the radio 
system used, and several systems of telegraph transmission are available 
(e.g.\ two\(hy or four\(hytone telegraph systems, frequency modulated systems,\ 
etc.). 
.sp 9p
.RT
.PP
1.2
However, frequency\(hyshift systems are in use on many routes and
the frequency\(hyexchange method (Definition\ 32\(hy32, Recommendation\ 
R.140) of 
operation is in use
on long routes suffering from severe multipath distortion.
.sp 1P
.LP
1.3
	\fISynchronous telegraphy operating at approximately 100\ bauds\fR 
 | see CCIR Recommendation\ 436\(hy2\ [1])
.sp 9p
.RT
.PP
Radiotelegraph channels that operate synchronously at a modulation
rate of 96\ bauds and employ automatic error correction are being increasingly 
used. The channel arrangement shown in Table\ 1/R.39 is preferred for 
voice\(hyfrequency multi\(hychannel frequency\(hyshift systems operating at a
modulation rate of approximately 100\ bauds over HF\ radio circuits. For   
.PP
frequency\(hyexchange systems (Definition 32.32, 
Recommendation\ R.140), the
central frequencies of Table\ 1/R.39 should
be used, and should be paired in the manner found to be best suited to the
propagation conditions of the route. (A typical arrangement would take
alternate pairs giving 340\ Hz between tones.)
.bp
.RT
.ce
\fBH.T. [T1.39]\fR 
.ce
TABLE\ 1/R.39
.ce
\fBCentral frequencies of voice\(hyfrequency frequency\(hyshift telegraph
.ce
channels with a channel separation\fR 
.ce
\fBof 170 Hz and a modulation index of about 0.8\fR 
.ce
(Frequency shift: \(+- | 2.5 Hz or \(+- | 0 Hz)
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
Channel position	Central frequency  (Hz)	Channel position	Central frequency  (Hz)
_
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
1	\ 425	\ 8	1615
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
2	\ 595	\ 9	1785
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
3	\ 765	10	1955
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
4	\ 935	11	2125
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
5	1105	12	2295
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
6	1275	13	2465
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
7	1445	14	2635
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
		15	2805
_
.TE
.nr PS 9
.RT
.ad r
\fBTABLE 1/R.39 [T1.39], p.\fR 
.sp 1P
.RT
.ad b
.RT
.sp 1P
.LP
.sp 2
1.4
	\fIStart\(hystop telegraphy at 50 bauds\fR 
.sp 9p
.RT
.PP
For several years, various Administrations have had in service, on
certain selected circuits, equipment with a channel spacing of 120\ Hz, the
central frequencies and frequency deviations of which are in agreement with
Recommendation\ R.35. The central frequencies of these systems are given in
Table\ 2/R.39.
.RT
.ce
\fBH.T. [T2.39]\fR 
.ce
TABLE\ 2/R.39
.ce
\fBCentral frequencies of voice\(hyfrequency frequency\(hyshift telegraph
.ce
channels with a channel separation\fR 
.ce
\fBof 120 Hz and a modulation index of about 1.4\fR 
.ce
(Frequency shift: \(+- | 5 Hz or \(+- | 0 Hz)
.ps 9
.vs 11
.nr VS 11
.nr PS 9
.TS
center box;
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
Channel position	Central frequency  (Hz)	Channel position	Central frequency  (Hz)
_
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 1	\ 420	11	1620
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 2	\ 540	12	1740
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 3	\ 660	13	1860
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 4	\ 780	14	1980
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 5	\ 900	15	2100
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 6	1020	16	2220
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 7	1140	17	2340
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 8	1260	18	2460
.T&
cw(48p) | cw(48p) | cw(48p) | cw(48p) .
\ 9	1380	19	2580
.T&
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\fBTABLE 2/R.39 [T2.39], p.\fR 
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\fB2\fR 	\fBRadio circuits whose frequency is greater than approximately\fR 
\fB30 MHz\fR 
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The use of voice\(hyfrequency telegraphy on line\(hyof\(hysight radio\(hyrelay
links and on trans\(hyhorizon radio\(hyrelay systems is under study.
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	\fBReference\fR 
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[1]
	 CCIR Recommendation \fIArrangement of voice\(hyfrequency telegraph channels\fR 
\fIworking at a modulation rate of about 100\ bauds over HF radio circuits\fR 
, 
Vol.\ III, Rec.\ 436\(hy2, ITU, Geneva,\ 1978.
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Blanc
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\fBMONTAGE: PAGE 38 = BLANCHE\fR 
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