EQUIPMENT OF A 24-CHANNEL MULTIPLEX TELEPHONE SYSTEM USING SYMMETRICAL LINE CABLES (K-24)

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP81-00280R000200030035-5
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 9
• Document Creation Date: December 22, 2016
• Document Release Date: April 8, 2011
• Sequence Number: 35
• Publication Date: October 30, 1956
• Content Type: REPORT

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 Sanitized Copy Approved for Release 2011/04/08: CIA-RDP81-0028OR000200030035-5
UIPNF (T OF A 24-CHANIIE;. MULTIPLEX TELEPHONE STSTE!1 USING
SY? 1ETRICAL L"+5 ABT.b5 K-
(Conclusion: For Beginning See No 5, 1953)
Vestnik Sr si f ommunication G. G. Borodsynk, Candidate Technical
News , No 6, 1953, Moscow, Sciences, Stalin prise laureate
Pages 3-6 G. N. Stepanov, engineer, Stalin
prise laureate
A. V. C heremstev, Candidate of
Technical Sciences
LINE AMPLIFIERS AND DEVICES FOR AUTOMATIC REGULATION OF THE
TRANSMISSION LEVEL.
The most important and the most widely used units of the X-24
apparatus, utilised in all the terminal and intermediate stations, are
the line amplifiers, which compensate for the attenuation of the line
sections in the line spectrum of the apparatus from 12 to 108 kc. These
amplifiers satisfy very rigid requirements with respect to many of their
parameters and particularly with respect to non-linear distortion, noise,
accuracy with which the frequency characteristics are corrected, and
reliability of operation. The need for satisfying the above requirements
is due to the fact that the group path of the apparatus, the currents of
24 channels, are being subjected to simultaneous amplification; in addition,
a large niunber of amplifiers may be connected to a single carrier-
channelised circuit, inasmuch as an average of 30 amplifiers is used for
each 1,000 km in each direction.
Line amplifiers of the following types are used in the K-24 apparatus:
amplifier without ALR, amplifiers with flat-sloping ALR, and amplifiers
with flat-sloping-curvilineal ALR.
Amplifiers with flat-sloping ALE are used both at flat-sloping
intermediate stations, as well as at intermediate stations intended only
for flat ALR. In the latter case the sloping automatic level regulation
are switched into the amplifiers manually when necessary, and sloping
ALR receivers are not installed.
Amplifiers with flat-sloping-curvilinear ALR are also us ---I in the
reception channel of the terminal stations; in this case they are called
reception amplifiers. In addition, among the line amplifiers one can
also include the transmission amplifiers, operating at the output of the
transmission channel of the terminal stations. Even though the trans-
mission amplifiers cannot be called line amplifiers in the full sense of
the word, nevertheless they approximate the latter, because they work in
the same frequency range and must satisfy the sane requirements as line
amplifiers with respect to many principal parameters; transmission
amplifiers differ principally only in that they have a flat amplification
characteristic.
In their principal portion, namely the amplifier element proper,,.
all the above-mentioned line amplifiers are identical and differ from
each other only in the external negative feedback chain and in the
correction networks connected at the input of the amplifier element.
The amplifier element proper contains three stages employing lOZh1L
tubes in the case of local supply and 12Zh1L tubes in the case-of remote
supply. To increase the power two tubes connected in parallel are used
in the output stage.
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 Special recently-developed tubes (typo 12Zh3L) used for remotely-fed
repeaters have all the characteristics of the 127h1L tube, but have a
considerably higher breakdown voltage in the cathode-fila.at portion.
Inasmuch as the filaments of the remotely-fed -=P34ier tubes in both
directions of transmission are connected in series, the operating
voltage between the cathode and the filament of the tube nearest to the
line is approximately 100. If the filament circuit of the tube should
be opened (for example, whenever one of the tubes is removed), the
voltage may rise to the maximum value used in remote 'supply (240 volts).
Therefore, to increase the operative reliability of the connection,
as the production of the 12Zh3L tube expands, it is necessary to change
over from 12ZhIL to 12Zh3L tubes in the line amplifiers of the
remotely-fed points. The above applies equally well to other remotely-
fed repeater stations of multi-channel apparatus, namely to the inter-
mediate stations of the K-12 system and to the VUS-12 stations.
A simplified diagram of a line amplifier with flat-sloping-curvilinear
ALR is shown in Figure 5. Heavy negative feedback is used in the
amplifiers to insure the required attenuation of the non-linearity and
the required stability of gain whenever the voltage of the power supply
fluctuates and whenever tubes are replaced. Two types of feedback are
used: external interstage and internal in the first and third stages.
The external feedback and the internal feedback in the third stage are
of the combined current and voltage type, while current feedback is used
in the first stage.
It follows from examination of Figure 5 that the amplifier differs
in its diagram from the line amplifier of the K-12 apparatus with res-
pect to the interstage coupling circuits, which contain also induction
coils in series with the aet.:ve plate load resistors. More substantial
differences are in the external negative feedback chain and in the
networks connected at the input of the amplifier. Placed in. the negative
feedback chain are: constant slope network CSN, corresponding to a line
section 8 km long, a set of lengtheners having a total attenuation of
1.3 nepers (in steps of 0.1 nepers each), a flat regulation device,
"flat LR." with limits of ? 0.5 nepers at 16 kc, as well as a network
for regulating the' curvilinearity, "cure. LR," with limits of ? 0.25
nepers at 64 kc.
Connected at the input of. the amplifier are filter X-12 and 5 line
equaliser networks L8, which slope the frequency characteristic of the
gain so as to correspond to ling sections 12, 6, 3, and 1.5 km in
length (a total of 28.5 kmi, and also a potentiometer that permits
adjusting the gain within limits of 2.7 nepers, in steps of 0.3 nepers
each.
The maximum gain of the amplifier at time highest frequency of 108
kc when the level regulating devices are in the central position is
8 ? 0.1 nepers. This gain is changed automatically when the cable
attenuation is changed by temperature with the aid of the ALR device.
Manual regulation is also possible, effected in this case by charging
the position of contact-making jumpers.
Because they contain fewer regulating elements, amplifiers with
flat-sloping ALR and without ALR have a correspondingly simpler feedback
chain. The constant slope network in amplifiers with flat-sloping ALR
corresponds to a line section 14.5 km long, while in amplifier: Without
ALR corresponds to a length of 20 km. At the input of these amplifiers
there is a set of line equalisers, corresponding to line sections 12,
6, 3, and 1.5 km in length (a total of 22.5 km). The maximum gain of
the amplifier without ALR is 8.3 ? 0.1 nepers, and that of an amplifier
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 STAT
with flat-sloping ALR with the regulating elements in the central position
is 8 0.1 nepers. All the valueii of section length given above pertain
to cables with paper-kordel? insulation.
Automatic level regulation devices intended for compensation of
temperature variations of the cable attenuation characteristics are
analogous in the K-24 apparatus with the?same devices used in the K-12
apparatus. The regulation is carried out without the aid of electro-
nagnetic mechanisms, by changing the resistanoes of indirectly heated
thermistors TR-l -- TR-3, operating in the feedback chain of the line
amplifiers. Control is effected by control-frequency current, received
by the control-channel receivers. The basic-difference lies in'the
introduction of a third automatic regulation, namely curvilinearity
regulation, intended for compensation of the deviation of the ii rement
in frequency characteristic of the.cable attenuation from a straight-line
law. The need for this regulation is considerably greater in the case of
the K-24 apparatus than in the case of the K-12 apparatus, owing to the
expanded frequency spectrum.' The curvilinear regulation is controlled
with a 64 kc control current, while the flat and sloping regulations are
controlled with 104 and 16 kc respectively.
The circuits of the control channel receivers of the K-24 apparatus
differ from those of the K-12 apparatus of the first versions in the
addition of a device that reduces considerably the operating process of
the level regulation, which occurs whenever several amplifiers with ALR
are connected in series and the level at the start of the trunk line
changes suddenly. At the present time this modification has also been
effected in the control-chamber receiver circuits of the K-12 apparatus.
CONSTRUCTION AND GROUPING OF APPARATUS: CURFtSNT OONSUl"TION
The K-24 apparatus is similar in its construction to the K-12 and V-12
apparatus. Many racks in the ter al stations are identical with the
racks of the K-12 apparatus. Among such racks are: the tonal-calling
rack (STV), differential-system rack (SVS), four-wire switching rack
(SChK), individual converter rack (SIP), carrier and control frequency
rack (SNK), remote-supply transmission rack (SDP-1), cable-circuit test
and signalization rack (SKTs), and lead-in and. switching rack (VKS),
used whenever line transformers are used for the carrier-channelised
pairs at an expanded frequency range up to 110 kc. The dimensions and
the capacities (depending on the number of channels served by the
equipment) of these racks are indicated in the description of the K-12
apparatus.
In addition, the terminal at.ation comprises also the group-
installation rack of the 24-chann?9l system (SGU). It has overall
dimensions of 646 x 2,500 x 450 mm, which is standard for long-distance
commurication apparatus racks. Placed on the SGU rack are the trans-
mission and reception amplifiers, the group rrsquenay converters, the
automatic level regulatioc devices, and other e2,ments of the group
channel used for 2 24-channel systems.
The repeater stations comprise the SDP-1, SDP-II, SKTs, and VKS
racks, which are identical with the racks of the K-12 apparatus. The
SDP-I and SKTs racks are used only for attended stations, and the
SDP-11 are used only in unattended stations. The attended stations
also contain intermediate-repeater racks SPU with amplifiers without
ALR, with flat ALR, with flat-sloping ALR, and with flat-
sloping-cu ilinear ALR, depending on the type of the stations. The unattended
stations are equipped with SPU racks without ALR and with remote supply.'
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 All the amplifier racks have overall dimensions of 646 x 2,500 x 450 mm.
With this, the racks without l!LR, those with flat AIR, and those with
flat-sloping /SLR carry equipment for 5 systems, while the rack with the
flat-sloping-curvilinear ALR is equipped for 3 systems. The terminal
stations may be equipped with artificial lines, the attenuation
characteristic of which is .-'uivalent to the attenuation of cables 8
and 14 ka long. These lines are used if the repeater section is of
shortened length.
The voltage of the porter supplies of the terminal stations should be
stabilised with an accuracy of ? 3%. The power supplies of the
attended intermediate stations should also be stabilised. The following
minimum voltag-,s at the output of the stabilizi:ig devices have been
established for the apparatus: plate voltage, 206 ? 3%; filament
voltage, 21.2 ? 3%.
The remote-supply current is stabilised automatically by voltage
regulators on the SDP-I rack, with an accuracy of ? 3%. The nominal
known voltage applied to the a p ifiers in the remotely-supplied points
is 160.
The average current consumption for the rack of the K-24 apparatus
required to supply the filament and plate circuits of the tubes and also
for the principal signalling circuits, is indicated in the -table.
Filament
battery
Plate
battery
STV
5.80
0.22
For one 24-channel
system
SChK
0.64
0.01
For one rack (up to
60 Ehannels)
SIP
3.80
0.17
For two racks (one
24-channel system)
SGU
1.2e.
0.13
For one 24-channel
system
SNK
7.70
0.50
For one rack (up to
five 24-channel
systems)
SKTs
0.25
For one rack
SPU with fl
SPU with fl
at ALR
at-sloping
0.64
For one 24-channel
system
AIR
0.90
For one 24-channel
system
SPU with fl
at-sloping-
For one 24-channel
curviline
ar ALR
1.16
0.15
system
SPU without
ALR,
For one 24-channel
remotely
fed
0.13
system
SPU without
ALR,
For one 24-channel
locally fed
0.05
system
The maximum rated gain of the intermediate stations of the K-24
apparatus is 8.2 nepers. However, it does not follow from this that all
the repeater sections may have an attenuation equal or nearly equal to
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 8.2 neyo rs, for 1n this case the noise level in the channels will be
ezceasive. To keep within the norm for the psophometric noise voltage
in the channels, the-attenuation of the repeater sections should be on
the average 7 nepers, and only in individual sections can it reach 8 to
8.2 nepers.
The locations of the repeater points (RP) are determined during the
design in the following manner. Starting with the average value of
attenuation, one obtains the rated length of the repeater section, which
is: 32 to 34 km for a cable with paper-kordel+ insulation and 37 to 39
km for a cable with styroflex-kordel? insulation. The proposed trunk
line is then subdivided into repeater sections, taking into account the
need of placing the RP in populated points and adhering as much ae
possible to the rated length. The maximum permissible length of a
repeater section cannot exceed 39 km for a cable with paper-kordel?
insulation and 46 km for a cable with styroflez-kordel? insulation.
The correct placement of the repeater points must be checked against the
expected value of the psophometric voltage of the intrinsic (broadband)
noise in the channel. The latter must not exceed 0.5 millivolts (at a
point with a relative level of -0.8 nepers) for a re-reception section
2,500 km long. If the re-reception length of the section is less, the
norm for the magnitude of the intrinsic noise in the channel can be
determined from the following inequality:
Un intr ( 0.5 L/2500 millivolts
where L is the length of the re-reception section in km. The above norm
corresponds to the accepted distribution of noise, in accordance with
which one quarter of the power, out of the norm for all types of noise
(1 milliwatt for 2,500 km) is allotted to the intrinsic (broadband) noise
in the channel.
The psophometric voltage of the intrinsic noise is the voltage
measured with a peophometer in the channel in the absence of-trans-
mission over the other channels of the system and over the channels of
the same name of the parallel systems. The expected value of the
psophometric voltage of the intrinsic noise in the upper channel, which
is under the worse condition, is calculated from the following equation:
Un intr"''.. 0.05 Vi e2 6 Si
where i is the number of the repeater section; N the number of repeater
sections; L631 the difference between the gain of the repeater station
and the avorage gain ( nSi - Si - 7); 0.05 the psophometric noise volt-
age introduced into the channel by a single repeater station with a
gain of 7 nepers.
(LNot7: The number 0.05 applies when the transmission power level
in the upper (24th) channel is + 0.5 nepers, i.e., when the trans-
mission level has a sloping frequency characteristic; if the character-
istic is horizontal and the transmission power level is +0.2 nepers,
it is necessary to substitute 0.07 for 0.05 in the equation.)_
Si = t' (1O8)Z + d P t(1O8) ?' ,
where {. is the length of the repeater section in km; f'( O$) the
per-kilometer attenuation of the cable at 108 kc and at a
given in nepers per kilometer; tl-\ tf Rt(1O8) the change in the
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 per-kilometer attenuation of the cable at 108 kc when the temperature
changes from the mailman to the minin+um, given in nepers per kilometer;
2'the distance from the preceding amplifier with ALR, given in km.
From the equations given it follows that to check the noise level
by calculation it is necessary to know within what range the soil tem-
perature changes at the depth at which the cable is laid (0.8 m) and
to specify the placement of the point that are equipped with amplifiers
with AI.R. For the majority of the regions of the European portion of
the U3SR it is possible to assume that at a depth of 0.8 m the soil
temperature fluctuates over the year from -4 degrees to -f 160 C.
The change in the per-kilometer attenuation of the cable is deter-
mined from the following equation:
Q (eft = Y ti P (t2 - t1 }
where P tl is the per-kilometer attenuation at the minimum temperature.
O(p the temperature coefficient of attenuation, tl the minimum temper-
ature, and t2 the maximum temperature. I- the cable has paper-kordel?
insulation with star twist and conductors 1.2 mm in diamter (copper),
then the temperature coefficient CC for 108 kc is found to ,~'nge from
6 x 10-4 to 8 x 101+ per degree. For a cable of this type r' 108) _
205 x 10-3 nepers/km and A t(108) = ? 3-3 nepers/km.
The placement of the points equipped with amplifiers with ALR is
made on the basis of the regulation limits and of the value of AP t.
The maximum distance between points with flat ALR can be obtained rom
the following expression.
C max (flat) - 0.7 .~ 230 km
A b t(1O8)
In practice it is recommended that amplifiers with flat AIR be
placed closer, so as to obtain a certain margin to provide for the
inaccuracy in the initial level setting and for the inaccuracy in the
initial data concerning the temperature fluctuations. Usually in the
design each third or fifth repeater point is equipped with amplifiers
with flat ALR.
The limiting distance between points equipped with amplifiers with
flat-sloping ALR is determined from the following equation:
?,max r?~f/sloping) - 1 R
o n~.(16) - Yt(1o8)
where L N t(lA) is tcce temperature variation in the per-kilometer
attenuation o the cable at the control frequency of the sloping
regulation, i.e., at 16 kc.
For a cable of the above type and for the above-mentioned tem-
perature-fluctuation limits we have /? (\(16) `" x 10-3 nepers/km,
and the maximum distance between points can be assumed to be approxi-
mately 500 km. Points equipped with amplifiers with flat-sloping ALR
rre located in practice every 10-12 repeater sections, i.e., 300-400
km apart. Amplifiers with ALR should be installed in points that are
equipped with independent sources of supply. One does not compute the
limiting distance for points equipped with amplifiers 'having flat-
sloping-curvilinear ALR; such points must be placed approximately
every 800-1,000 km.
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 To determine the location of the amplifier points with ALR in the
case of trunk lines equ-cped with cable with styroflex-kordel* insula-
tions, it is necessary to find the coefficients Ar t(lo8) and L (16)
corresponding to the projected cable.
When locating the repeater points it, is necessary to take into
account that the maximum gain of 0.2 repers Car. be used only between
points equipped with amplifiers without A.LR,, The :r,axin.um attenuation
of a repeater section (at the minimum temperat.:re), adjacent to a
point equipped with ALR. must not ex,'eed 7.5 netrers. Consequently,
the maximum permissible length of such a section is 3b.5 km for a
cable with paper-kordel' insulation and 42 }Jn for a cable with styroflex-
kordel? insulation.
When the calculations are made one mu-it bear in mind that reducing
the gain in short repeater sections results In noise improvement. This
improvement can be taken into accoumt only when regulating the gain in
the feedback chain. The limits of this rgulation are restricted to a
minimum value of 6.8 nepers for amplifiers w;th ,**LR and 5.5 nepers for
amplifiers without ALR. Thus, if the vale of obtained during
the calculation of the gain (S,) is less than the above, the value of
P(108)1 should be assumed to- to b.8 or 5.4 ne ers respectively.
The noise levels in the channels were meal .red di.-rang the line
and operating tests of the K-24 apparatus, performed on an experimental
section of the trunk line. With this the measured values agreed with
the calculated ones, obtained with the above equations. The difference
between the measured and calculated val:_ee dia not exceed 10%.
Experimental operation of the appar