EQUIPMENT OF THE K-12 12-CHANNEL SYSTEM (CONCLUSION)

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP81-00280R000100060029-7
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 10
• Document Creation Date: December 22, 2016
• Document Release Date: April 1, 2011
• Sequence Number: 29
• Publication Date: September 27, 1956
• Content Type: REPORT

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 (Conaluslon; for first par- &e So 6, 1952)
Ves t 9",421 (COMMMIC&S. long
Herald), Ko 7, 1952, Nosraw,
Pages 3-6
G. G. Borodzyuk
and F. A. Adahe^ov
Line Amalifi.rs
The principal units of the K-12 apparatus, constituting a part of
all terminal and intermediate stations, are the line amplifiers. In
accordance with the 3 types of intermediate stations, 3 types of line
amplifiers are used in the apparstust without AIC, with flat ALC, and
with flat and sloping ALC. The latter amplifiers represent the most
complicated type and are employed not only in the intermediate but also
in the terminal stations where they are called the line reception
amplifiers.
All line amplifiers contain the same principal portion -- the
amplifier proper; they differ from each otbar only in the external
(interstage) negative feedback chain and by virtue of the fact that they
have a set of correcting networks connected at the input of the amplifier.
The same principal portion of the amplifier, with slight variations and
with a very simple external feedback chain, is used as a transmission
amplifier at the terminal station; this amplifier has an amplification
characteristic that is independent of the frequency.
The simplified principal diagram of the line amplifier with flat
and sloping ALC is shown in Figure 6. The doted lines divide the
circuit into portions whose elements are placed in individual blocks.
Ttrs amplifier-proper block, which is identical in the line amplifiers
of all types, is shown in the right upper part of the diagram. It
contains 3 stages of amplification employing lOZhlL tubes if local electric
supply is used or 12Zh1L tubes if remote supply is used.
The first 2 stages with tubes V1 and V are voltage amplifiers, and
the last (output) stage with 2 tubes V3 ani V in parallel is the power
amplifier. The stages of the amplifier are resistance coupled. The fixed
bins is produced on the contr'l grids of the tubes by a voltage drop duo
to the d-c components of the plate currents and screen-grid currents across
the corresponding resistors connected in the cathode circuits of the tubes.
Heavy negative feedback is employed in the amplifier, insuring
stability of the amplifier with fluetuntions in the source of supply and
the required nonlinearity Attenuation in the amplifier. Three negative
feedback chains are used: one outside interstage chain and internal
chains in the first And third amplification stages. The external chain
And the internal chain in the third stage produce a combined current
and voltage feedback. The internal feedback in the first stage is current
feedback.
A potentiometer connected at the input of the amplifier ponnita
frequency-independent variation of the gain in maps of 0.3 nepera each
to eompenaate for the attenuation of line sections of different lengths.
With the aid of this potentiometer it is possible to adjust the gain
within a range of 3.9 nspurs.
 A so-called constant elope network CSN is connected in the external
feedback chain to compensate for the slope of the frequency attenuation
characteristic of a cable-line section 30 km long. Connected at.-the
input of the amplifier are 4 equalizing-networke EN having characteristics
that slope in a direction opposite to the frequency characteristic'of the
cable-line attenuation of different length, and an actual-slope network
with a characteristic corresponding to the Actual attenuation characteristic
of the cable line. By using these networks in varying combinations and by
reconnecting the input potentiometer and the lengtheners -- which have
a total attenuation of 1.35 nepers (in steps of 0.15 nepers each) -- in
the amplifier feedback chain, the resultant frequency characteristic of
the amplifier gain is made to compensate for the attenuation of amplifier
sections ranging from 20 to 54 km in length, with an accuracy to within
one ka. All these reconnections are.-effected by means of soldered joints.
It is possible to change the frequency characteristics of the amplif i-
cation of the amplifier without resoldering the connections (by changing
the settings of contact.juapsrs)with the aid. of variable resistors A and
B which are connected in the external negative feedback chain. The former
of these resistors is connected directly into the circuit, and the second
is a load resistance for network C. The main purpose of resistors A. and B
and of network C is to adjust the gain of the amplifier so as to compen-
sate for variation in attenuation of the cable line produced by temperature
fluctuations. Resistor A makes it possible to change the gain by an
equal amount at all working frequencies within a range up to ?0.35 nepers.
Resistor B together with network C permit changing the slope of the
frequency characteristic of the gain in such a way that the value of gain
at 12 kc changes within a range of up to ?0.55 nepers, while the attenuation
remains almost constant at 56 kc.
The frequency characteristics of the gain of a line amplifier with
flat and sloping ALC at different lengths of line section- compensated
by this amplifier and at an average temperature of ?50 are shown in Figure
7. The same figure shows dotted the amplification characteristics, which
are obtained at the extreme values of resistors A and B for the limiting
values of section length, namely 20 and 54 km.
Amplifiers with flat ALC contain only one fJ network at the input;
in all other respects this amplifier is a complete duplicate of the
amplifier with flat and sloping ALC.
The amplifier without ALC differs from the amplifiers considered
above in that it has no P21 network but has a principal-slope network in
the feedback chain to insure equalization of the characteristics of a
44 km cable line, and also has not one but 3 actual-slope networks at
the input. The feedback chain of the amplifier without ALC is provided
with a set of lengtheners adding up to 2.05 rather than 1.35 nepers. This
amplifier is designed to compensate the attenuation of amplifier sections
ranging from 20 to 57 km with an accuracy to within one km.
In addition, line amplifiers with flat ALC and without ALC contain
a low pass filter, which protects the input of the amplifier against the
entrance of noise in the frequency range below 12 kc, produced principal-
ly by crosstalk from low-frequency pairs in nonloaded cable pairs.
The use of gain adjustment and constant-slope networks in the nega-
tive feedback chain of the line amplifiers reduces considerably the effect
of thermal noise produced in the resistances connected at the amplifier
input. Were all the gain and frequency-characteristic slope adjustments
 to be effected with the aid of equalizing networks and length.ners con-
nected at the amplifier input, the thermal noise would in all cases be
at a level corresponding to the maximum gain used for the compensation
of a maximum-length section.
The heavy negative feedback in the amplifier, amounting to approxi-
mately 5 nepers at 60 kc for an average length of section (external feed-
back plus feedback in the output stage) also reduces considerably the
nonlinear distortion introduced by the ampiitier. The characteristics
of the dependence of the nonlinearity attenuation in the second and third
harmonics on the output level of the amplifier (power) are represented
in Figure 8. The measurements were made at the indicated 60-kc harmonic
with an amplifier gain equal to 6.8 nepers.
The accuracy with which the frequency characteristics of the line
attenuation are corrected with the aid of networks in the line amplifiers
is sufficiently accurate. However, if there are many amplifier sections,
the correction errors accumulate and their sum may become excessive.
To eliminate these errors the K-12 system employs supplementary correcting
networks (equalizing systems) installed in the intermediate and terminal
points of every fifth or sixth amplifier section.
Installations for Automatic Control of the Transmission Level
The K-12 apparatus employs purely electrical automatic level control,
effected with the aid of thermistors. With this, 2 separately acting
automatic level controls are employed, each regulated by an independent
control-frequency currents "flat," using a 56-ke control frequency, and
"sloping," using a 16-kc control frequency. The above currents are
transmitted over the line in both directions.
It was indicated in the description of the line amplifier circuit
(Figure 6) that by varying resistances AB, connected in the external
feedback chain of the amplifier, it is possible to change the gain of
the amplifier independently of the frequency ("flat" control) and to
change the slope of the frequency characteristic of the amplifier
("sloping" control). It is possible to replace rea&stprs AB in the nega-
tive feedback chain of the amplifier by indirectly-heated thermistors
Tr-l and Tr-2 of the TKP-300 type. The resistance of the thermistor
is regulated with the aid of its heater circuit using the corresponding
control-frequency current. The working body of the thermistor, made of
a semiconductor and having quite small dimensions (fractions of a mm)
is surrounded by the heater winding and is placed in an evacuated glass
bulb. A typical characteristic of the dependence of the working-body
resistance on the heater current for the type PKP-300 thermistor is
shown in Figure 9. The maximum power dissipated by the heater winding
is 20 mw.
Automatic control insures the constancy of the level of control-
frequency currant at the output of the line amplifier with an accuracy
of ?0.07 nepern at a change of lovel at the input of amplifier by ?0.35
nepers in the case of flat regulation and ?0.5 nepers in the case of
sloping regulation (at the 16 kc frequency). For the 12 kc boundary
frequency of the line spectrum the limits of the sloping regulation are
+0.55 nepera. Such limits result in enough compensation for variations
in cable attenuation resulting from fluctuations in soil temperature to
cover 3 amplifier sections employing flat regulation and 9 amplifier
sections employing sloping regulation.
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In the receiver channel of the terminal stations the control fre-
quency currents are separated from the total transmitted spectrum by
narrow-band uartz filters connected in parallel with-the output of line
amplifier A (Figure 3); from there the currents flows into the input
of the control-channel receiver (CC rec). In the latter they are '
amplified, converted into 3 kc auxiliary-frequency currents. and applied
to the heater winding of the thermistor.
The control channel receiver circuit is so designed that insigni-
ficant fluctuations in the control frequency current at the output of
the line amplifier cause very large changes in the auxiliary frequency.
current applied to the heater winding of the thermistor. This results in
the required limits and accuracy of the control. The receiver contains
2 type lOZh1L tubes and an auxiliary indirectly-heated thermistor. The
first tube is used to amplify the control frequency current and to
generate the auxiliary 3-kc frequency. The second tube is used to amplify
the control and auxiliary frequency currents. The thermistor serves to
control the power of the.3-kc frequency..
If the trunk line is very long (above 2,000 km) the use of automatic
level control of the 2 types (flat and sloping) may be.inadequate. This
is explained by the possible accumulation of errors due to the deviations
of the frequency characteristics of cable attenuation from a straight
line. To compensate for the above errors, it is proposed to introduce
a third level control, the so-called curvilinearity control, for which
a third control frequency is required.
Remote SuDDLv Installations
The K-12 system employs remote supply of the unattended amplifi-
cation points, using a circuit consisting-of 2 cable conductors, (over
which the high frequency communication is also effected) and the ground.
This circuit is produced by using the center taps of the line transformers
as shown. in Figure 10.
In the station which provide3 the'remote supply, the voltage from
the plate battery is applied to the center top of the line transformer
through a carbon pile voltage regulator AVC1, fuses, and a polarized
signal relay R. In the supplied station the remotely-supplied voltage
is applied from the center point of the line transformer to the winding
of the switching relay R3 and in parallel thrcigh contacts of this relay
to the series-connected filaments of the tub if both amplifiers of the
12-channel system.
The carbon pile regulator.AVC1 serves to maintain the remote-supply
voltage constant. One end of the coil of its electromagnet is connected
through-the winding and contacts of relay R1- 1 to the point at which
the remote supply is fed. The second end of this coil is connected through
contacts of relays Rl_l and R1-2 and through the winding of polarized
signal relay R?_1'to the center tap of the line transformer of a separate
pair in the cable, at which the center top of the line transformer is
grounded at the supplied station. When so connected, the AVC1 regulator
compensates for the variations in cable conductor resistance, occurring
through the entire amplifier sections as a result of temperature changes,
and maintains constant the remote-supply voltage at the fed point.
If all the nonloaded cable pairs are used for carrier. telephony,
then the center points of the pair of loaded low-frequency group of k
conductors is used for the electromagnet winding circuit. To prevent
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the do field of the supply current from magnetising the loading coils
of the phantom networks of the low-frequency pairs, the coil of the
electromagnet of a second carbon pile regulator AVC2 is connected to the
center point of the transformer of the second pair of loaded group of
4 conductors.
If damage occurs to the circuits feeding the coil of the electro-
magnet of one of the carbon pile regulators, relays R1_1 and 81_2
disconnect the circuits of the electromagnet coils from the center points
of the transformers of the loaded pairs, grounding them through resistors
R2_1 and R2_2, which equal to the average value of the resistance of the
disconnected circuits. This prevents the magnetization of the loading
coils of the phantom networks.
Polarized relays R and R2.1 are used to signal any change in the
remote-supply current.
Relay R3 in the supplied station insures automatic switching of the
remote supply to a spare source (for example, to a second neighboring
attended station) whenever damage occurs to the supply over the principal
circuit. Protecting chokes Ch, connected if necessary in series with the
filament supply circuit, serve to protect the latter from induced com-
mercial frequency currents, which say occur in case of faults in high
voltage lines that pass parallel to the communication cable line. One
carbon pile regulator can serve up to 11 remote-supply circuits.
Entrance and Switching Installation.
An entrance-switching rack (VKS) and an auxiliary testing and
signalization cable line rack (9KT) are used for the entrance equipment
of interurban cables.
The entrance switching rack is intended for connecting the inter-
urban cable and also to protect the station equipment and the service
personnel against dangerous voltages which may be induced in the cable.
This rack permits replacing some pairs of cables by others and also to
carry out control measurements over the cable. In addition to 4 boxes
with terminal strips, which have shielded or nonehielded to nninkls, this
rack carries...the line transformers, the protective discharge gape, and
the induction coils. The latter are connected in the center-tap circuit
of the line transformers and serve to increase the crosstalk attenuation
between cable pairs. Cables with high and low levels (transmission and
reception) are connected to different entrance-switching racks.
The VKS racks are mounted on porcelain insulators. The sheaths of
the cables entering into the cable rack and the cable hangers are insulated
from the ground. In addition, the racks to which low and high level
cables are connected are insulated from each other. Rubber mats should
be placed ahead of the VKS. The racks must be insulated from the ground
so as to prevent possible cases of shock to the service personnel whenever
high voltage occurs in the cable.
Mounted on the rack for cable-circuit test and signalization are
the signalization elements that operate whenever the compressed air
pressure in the cable drops, a sot of relays for the service lines, and
the conversation-calling installation. It is proposed in the future to
mount on this rack a d-o bridge for cable measurements. The SKTS is
also insulated from the ground.
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Construction and Assembly of Apparatus -- Current Consumption
The K-12 apparatus is made up in the form of racks. Many of the racks
have dimensions and constructions that are standard for all.domestic long
distance apparatus of most recent models. The majority of tacks can carry
units'for several 12-channel systems.
The terminal station is made up of the following racks: .(1) tonal-
calling rack STY, which provides room for 24 receivers and 3 tonal-calling
generators; (2) differential system rack SDS,which can carry up to 108
differential systems (3 differential systems on each panel); (3) 4-wire
switching rack SCHK, designed for mounting a measuring instrument (neper
meter), conversation-calling installations, and 5 panels with 4-wire
switching terminals and low-frequency amplification regulators, each
panel serving 12 channels; (4) individual converter rack SIP, intended
for mounting the individual frequency converter with the associated pass-
band channel filters and low-frequency amplifiers, for one 12-channel
system; (5) group installation rack SGU, on which are mounted the line
amplifiers for transmission and reception, group frequency converters,
and other elements of the group channel, and also ALC installations for
3 12-channel systems; (6) carrier and control frequency rack SNK, which
can insure carrier and control frequency supply to 10 12-channel systems.
All these racks measure 646 x 2,500 x 450 mm.
In addition to the above racks, the terminal station contains the
following..
1. Remote supply transmission rack SDF 1, having a capacity of 22
circuits; its dimensions are 526 x 2,500 x 450 mm.
2. Entrance-switching rack VKS. A rack of this type is designed
for installation of 4 boxes each having 2 terminal boards. The capaci-
tance of. the terminal strip with shielded terminals is 6 pairs of cables,
and one without shielded terminals is 10 pairs of cables. The rack
contains 64 positions for placement of transformers and inductance coils.
The dimensions of the rack are 600 x 2,500 x 680 mm.
3.' Cable circuit test and signalization rack SKTS. This rack is
placed,in the same row as the entrance-switching racks. The dimensions
of the rack are 526 x 2,500 x 450 mm.
The intermediate amplifier stations are provided with intermediate
amplifier racks SPU. If the SPU rack is installed in a station having
automatic level control, then in addition to the line amplifiers this
rack carries also the control-channel receivers. The capacity of each
rack permits the mounting of equipment for 5 12-channel systems. The
dimensions of the rack are 646 x 2,500 x 450 mm.
In addition to the intermediate amplifier racks, the attended inter-
mediate stations, which provide power for remote supply, should also con-
tain: (1) entrance-switching VKS racks whose number is determined by
the capacity and purpose of the cables, (2) cable circuit test and
signalization rack S;KTS, and (3) remote Supply transmission rack SDP-l
(Figure 11). The last 2 types of racks are not installed in remotely-fed
unattended..amplification points, which are provided only with remote
supply reception racks SDP-II. The maximum capacity of the SDP-II rack
is 20 circuits; its dimensions are 526 x 2,500 x 450 mm.
 The cement. canstr l by the k-12 apparatus for the ripply of time
f Ilam*nt a4-.! plate tirrstits of tin tubes, As nil as for the principal
sig".al circvlta. IF shown in the table.
Cvrrt t Consuption
aspares
Ranks
f !hearer
battery
2.90
plate
battery
0.11
for one 12-channel
SChM
0.62.
0.01
systa
for one rack
SIP
1.90
0.085
for one 12-channel
SCU
1.00
0.10
system
same
SNK
7.70
0.50
for one rack
SKTs
0.25
-
same
SPU with flat ALC
0.65
0.08
for one 12-channel
same, with flat and sloping
ALC
0.85
0.10
system
same
same, without ALC (remotely
supplied)
-
0.12
same
same without ALC (locally
supplied)
0.43
0.06
same
The nominal voltage of the source of filament supply is 24 v, and
of the plate supply source is 220 v. However, for the SCU, SNK, and
SPU racks with local supply it is necessary to stabilize the voltage of
the supply sources with an accuracy of ?3%. The voltage at the output
of the stabilizers will therefore be lower and may reach 21.2 ? 3% for
the filament circuit and 206 ? 3% for the plate circuits. The remote
supply is applied to the SPU rack from a plate voltage source with a
nominal rating of 220 v, whereby the remote supply is stabilized, as was
already indicated, with the aid of AVC regulators at the SDP-I rack.
The STV and SIP racks can be fed, as in the V-12 apparatus, from
stabilized or unstabilized sources of supply, with barreters used in
the latter case for the filament circuits, thereby increasing the
filament consumption by 33 percent as compared with the values indicated
in the table.
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