SUPPRESSION OF RADIO INTERFERENCE CREATED BY TELEGRAPH COMMUNICATIONS EQUIPMENT

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP81-00280R000100060032-3
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 7
• Document Creation Date: December 22, 2016
• Document Release Date: April 1, 2011
• Sequence Number: 32
• Publication Date: September 24, 1956
• Content Type: REPORT

Sanitized Copy Approved for Release 2011 /04/01
CIA-R DP81-002808000100060032-3
A Next 1 Page(s) In Document Denied
Sanitized Copy Approved for Release 2011 /04/01
CIA-R DP81-002808000100060032-3
 SUPPRE33ION OF RADIO INTERFERENCE CREATED
BY TELEGRAPH COMMUNICATION3 EQUIPMENT"
? Vestnik svyazi [Communications
Herald], No 12, December 1955,
Moscow, Pages 8-10
M. H. itabinovictt
V, Y, Iioditi
A discussion of the sources of radio-interference in telegraph
equipments, their means of propagation, and methods of supgrkasion.
Examples of interference suppression in telegraph equipment ore
given.
Telegraph equipment and devices causing sudden changes of curretzt and
voltsge in electrical circuits interfere with radio reception, In the space
surrounding the equipment high-frequency electromagnetic fields are created,
and'at the terminals as well as between the terminals and the teouai.ngs of
equipment there occur high-frequency interference voltages with a continuous
spectrum, embracing almost the entire range of frequencies usedi'or radio
broadcasting and television. The intensity and degree of the interference
depends on a whole .aeries of causes in which the design of the source of
interference and the number of current or voltage changes per sec-and az?e
of considerable importance.
In moat asses the sources of interference in telegraph equipments are
commutator drives and contact devicea?(motore, keys, cam distributors,
.sounders, etc) changing. (switching) the value-end direction of current
100 or more times per second. ;~
.~:L .;
yu ~(p
The sparking accompanying''~ir;le switching process scorches the .contacts,
resulting in unreliable conduction ticross the latter, In order to reduce
-this harmful affect in?niany telegraph systems a spark quencher (the circuit
consisting`f R and C in Figure 1) yi$.?connectod in parallel with the con-
tacts, The spark-quenching circuit not only facilitates contact operation
but also provides a.?parallel path for transient current and reduces the
intensity of interference with radio reception. ,
The 'radio interference created by telegraph equipment is propagated
by direct radiation into spuce and- along ~~he conductors r-onnec.Cead Witt,
this equipment, Over especially long distances (several kildmcters) radio
interference is propagated along power'and telegraph wzres and along light-
in~, telophono, and signalling cirauits;closo to these wire~?. Esl~~nsivr:
branching of interference-carrying circt4lts complicates the task of car,--
batting radio interference along the paths of its propagation,
In most cases the adoption o~ anti-interference measures at the recr~iv-
ing site does not afford aufficient?~'~?eduction of interference w.i t.h radzr,
and television reception. Interference penetrates a radio reo.:iae,? r:hit':%!y
through capacitive coupling betweon,~the receiving antenna and the inte.r?
forence-carrying circuit, The most thorough method of combatts.ng induc~triral
interference is its suppression directly at the sources, though rr~~n unum
precautions must always bo observed a't the receiving site and al.or,g the
paths of interference propagation (by cor,,rect orientation of l.h~ receiving
antenna, isolation of interference-oa.z~iying circuits by biocking capacit:or5,
etc). i kr'~
The pormissiblo irt~`ensity of industrial lnt?rferenc.r+ creatr~d Ly the
different sources is r ulatod,~by special standards. (State Radio [u::pectlrm.
r
 ~STAT
Ninlatry of ~ommunicationa USSR, Normy predel'no dopustimykh induatrial'nykh
radiopomekb.[Standards for liaximum Permissible Industrial Interference ,
tb.ird edition, Sv,yaz'iadat, 1954, it?ms 9a-g). In these standards, according
to the location of the source of interference and the purpose of the power
supply. system, all telegraph equipment is divided into the following three -
catQgories:.a, equipment installed in a non-residential building and fed
from an industrial power system; b, equipment iateuded for use in a.resi-
dential building. or connected to the publlc.,.power system; c, equipment
located in the immediate vicinity of a radio receiver, All. three. categories
-of telegraph equipment are rated according to the field intensity and accord-
1.r.g,to the voltage between the terminals and tho rousing of th? equipment
Moreover, in ezties with cable telegraph systems a, central telegraph .
office occupying an individual building is regarded as one general source.
of radio interference. The radio interference created by such enterprises
is rated only according to the field intensity.at a distance of ten meters
from the building, since it has been established that the radio interference
of a cable sgatem attenuates rapidly and does not carry over to systems
connected with receiving antennas.
The standards distinguish sources of radio interference connected to
the power lir.ea of residential buildings as (a) with a duration o3 mors
thaix one secr~n3 regard lass of the rate of recur?rance and (b) Ffth a dura-
tion of one second or less but repeated more often than once eVeT'y live
minutes.
Radio interference caused by circuit breakers and knife switches is.
not included in the standards. '
The intensity of radio interference is determined by means of,specaal
instruments, circuit noise motors. Ia order that the results oi'. measurements
under different conditions may be compared, the methods of measurement of.
interference and the parameters of typical meters are also specified in the
standards. The IP-12 circuit noise meter has found wide use in the Soviet .
Union for measurements in the long-, medium-; and short-wave ranges (0,15-
'LO IVIc) and the IP-14 meter for measurements in the ultrashort-wave range
('10-150 Mc).
Suppression of radio, ir_terferenre '.s usually achieved by -means of fil-
tora connected to the interference-carrying conductors of telegraph equip-
ment as well as by shielding the uources of interference in those cases
where it is necessary to eliminate the fields of direcily radiated iniar-
f.i~ r?nCe .
In order that the equipment required for su{,pression of radio inter-
ference may be as simple and economical as passible it is necaaeary to
sa3r.-,h for possibilities of reducing the intensity of interference created
try the sources themselves. In certain telegraph equipment this may be
achzovc~d by careful connection of the components of the telegraph cir--
~:uzts, wherein the equivalent internal. impedance of the source oY inter-?
le.rence relative to high frequencies is as great as possible, cram the
formula
UL E
ZL
(ht re E is the emf of the source of interference, Z1 is the internal im?-
prdunce of that source, and 'LL is the load impedance) in determining the
 interference voltage drop across the lead it is apparent that, all other
conditions being equal, an increase in the internal impedance ~i is ac-
companied by a decrease in the interference voltage across the load. Hence.
in developing telegraph circuits it is desirable, wherever poaaible,"to
connect components with resistors and inductances at the sending end and
to place them in the immediate vicinity o3 the source oY interference.
Such connection, in increasing the ia~pedanos of the transmitting section
of the circuit, permits reduction of the interference voltage in the~net-.
work and in the load, and in a Yew cases permits limiting the use of
blocking capacitors to single unite so that the intensity of residual
interference meets the requireaents of the standards.
Tho balancing method prceea esgecial3y effective in suppressing radio,
interference. This method consissa in the symmetrical connection of all
the windings of electrical equipment of a given circuit relative to the
spark contact; the windings are divided into two equal sections and are
connected to both conductors of the source of interference, wherein they
play the role of an inductor and at the same time balance the asymmetrical
interference voltages between each conductor and the ground. With the
voltages between the conductors and ground equal in value and sign vela-
tive to ground, there are crested mutually compensating electromagnetic
fields Having no effect on the antenna,
In balanced schemes the suppression oY inter,erer_ce in compliance
with the standards can in zaos?T cASes be ar,.}ig,sva,~, by si~:Ip1e ne9na without
significantly increasing the cost of Lhs ~~gr::ipy~.=.'n~t. cai?!?ure to take ad-
vantage of the possibilities for interference suppression by electrical
balancing often lards to an un,~usti?ied incrc-.see in the ultimst:e CDSt, of
equipment. For example, in the ST-35 t:~l~agrae:?a oquipm?s2t prod''uced in
1984 interference is suppressed by a bulky arr?sng~ament consisting of.s
.two-section motor filter and throe single-sRCt:ion,f~lters --~..a line filter
a trans>citter'filter, and a receiver filter. On the other hand,. if in
developing the arrangement ?or interferFnro tsupprese..on conside.ation
had been given to the possibilAty of symmet.ical conaecti.on :~f the exciter
windings of the DT'A-40 motor r~ilative to its contact speed regulator and
symmetrical connection of the windings 7F'thA receiving? electromagnet
or the receiving relay relative to the contacts of the te].e~;raph trans-
mitter, then the interference suppressing arrangemenk of rho equipment
could have been simpler and less expensive.
During operation it is necessary to maintain the telegraph equipment
and mechanisms in working condition. It is necessary that the motor brushes
.make good contact witi2 the commutator and that the contact surfaces of the
relay and the speed. regulator not be corrodes, for otherwise the intensity
of radio interference will he considerably increased, Vibration oP.the
components and interference suppressing filters lowers the effectiveness
of the suppression. Hence, careful fastening of all the components and
wiring in the ,eq~~ipm6nt 13 IlecetiSa Z'y,
Let us examine a few examples of suppression of radio interference
in telegraph equipments. (?. A, Aleshin took part in dev~+lapir_g the des-
cribed methods of Interference suppression,]
1. Suppression of Radio Interference Created by the I4I-44 QMorse) Telegraph
Equipment
Equipments oP the M-?44 type are inetsAled in communications offices
and departments in which communications equipment and radio equipment may
be placed close together in the same premises. The intensity of radio
interference caused by the M?-44 equipment is as high as 700 times greater
t}Ian allowed under the standards (item 9r.); with a radio receiver turned
 Sanitized Copy Approved for Release 2011/04/01 :CIA-RDP81-002808000100060032-3
on telegraph keying is clearly heard in the loudspeaker, interiering with
the reception of radio broadcasts.
Figure 2 shows a method oP suppressing interference caused by'the.H-44
equipment operating on d-c with'-a line voltage not exceeding 200 v. The coils'
of the electromagnet aro symmetrically connected to the line and battery
conductor relative to the operating contact of the key. The telegraph key
is placed in a grounded shield. However, in connection with the difficulty
of making the shields, equipment already~placpd in operation may be operated.
with the key placed on a grounded metal pli[.te -- on the condition that the
radio receiver employs an external antenna and the tele eph equip'sfent is
located ~lQt leas than tao meters away from the radio re? iver.
? The knob of the key must be made of an insulating material, for 11
during keying the hand of the operator is in contact with tha metal army
of the key, the strength of Lhe intereterenco will be increased by Several
The components of spark gLencher Rs end C$p must be placed in the im-
mediate vlcinity of the key so that the ~onnectiag sires between the key
and the filter will be as short es possible. Filter capecitora Ci must be
fastened inside the base of the equipment close to the coils ofithe electro-
magnet. The housing of the clockwork aechaniam must be grounded. I~t is cesir-
able that the telegraph circuit of the !l-44 equipment end the antenna circuit
of the radio receiver have separate grounds. .
2. Suppression?oi Radio Interference Created by TR~1 end RP-4 Telegraph Relaga
Polarized TRIS and RP-4 relays, designed for operation in the ciicuits of
telegraph equipment installed on the premises of central telegraph offices
and city communications departments, cause radio interference considerably in
Figure 3 shows the circuit of an interference suppressing filter for
telegraph relays with polarential keying,?which circuit insures compliance
with item 9b of the standards. The circuit contains one inductor, consisting .
of two coils (L1 33 milliherries) of 1,110 turns of PEL-0.2 wire each. The
two-section coil form is fitted over a core of transformer steel. The di-
menaions of the Plates are 3.8 x 43 mm with a thickness of 0.35 mm. The stack
is 3.8 mm thick.
With grounding of -the auxillary..Winding of the RP-4 relay the residual
interference voltages at terminals f-$ of the operating windings are decreased.
Hence, if the layout of the telegrap~,ti'equipment permits such connection, it
is recommended that terminal 12?of the RP-4 relay be grounded. .
All the components of the filter (capacitors, coils, resistors) must be
placed in a grounded Shielding container with output posts. In order to min-
imize coupling .between the input and output posts of the filter they must be
placed on opposite sides of the container. The filter itself must be loca-
ted next to the relay terminals in order that the wires connecting the two
will be as short as possible. The wires leading to the input and the output
of the filter must not be led through a common braid:
Tne relays must be covered with shield packets and the terminal strips
must be placed on a metal panel.
~otinection of the interference suppressing filters does not increase the
distortion of telegraph signals; it merely causes a negligible rounding of
the leading edge of the signal.
,,.
Sanitized Copy Approved for Release 2011/04/01 :CIA-RDP81-002808000100060032-3
 STAT
3. Suppression of Radio Interference Caused by the Call Set of the Automatic
Subscriber Telegraph (AAVP-1)
The AAVP-1 "call net contain'contact mechanises (digit selector, push-
buttons, telegraph and telephone relays) which cause interference with radio
reception. The call sets are installed in institutions, industrial enter-
prises, end also in the citq`coiamunicationa sections usually found 'in
residential buildings.
The most intense source of radio interference in the call set is the
digit selector. In dialing a number the interference voltage in the long=
wave range reaches 25,000 microvolts in a duplex telegraph circuit and 3,500
microvolts 1n a simplex circuit.
Since a subscriber's number. may consist of several digits and one second
is required for the transmission of a digit, operation of the digit'selector
may have a prolonged disturbing influence on radio reception. Hence, inter-?
Terence from the digit selector of the call net must be suppressed.'
The problem of suppressing radio interference oreated by the other ,
sources is solved differently. While the intensity of these interferences
is also considerable (for example, at the terminals of the call net in turn-
ing the motor on and oii, the interference voltage at a frequency of 0.16
1!c reaches 8,000 microvolts), their duration does not exceed"a second. 1lore-
over, they appear in the fora of distinct clicks, and the number of connec-
tions o! subscriber equipmr,nt during maximum traffic does not exceed nix per
hour. Hence these ere not included in the standards for maximum permissible
radio interference and their suppression is optional. Thus, notwithstanding
the fact that the call net contains several saurcee of intense radio inter-
ference, only the interference from the digit selector is suppressed.
Figure 4 shows the diagram of the transmitting circuit of an AAPV-1
call set in which the digit selector is connected with ari'interference
suppressing filter L1C1. The arrangement contains an inductor consisting
of two coils (L1 20 millihenries) of 850 turns of PEL-0.2 wire each. The
two-section coil form is fitted over a core o! transformer steel. The di-
mensions of the plates are 3.8 mm x 43 mm with a thickness of 0.35 mm. The
stack is 3,8 mm thick.
In order that interference from the dig~t selector will not be induced
in the receiving and motor circuits the rote ference suppressing filter
must be placed in~the immediate Ticigity. of the digit selector.
4. Suppression of Interference Created by TV-39 Automatic Telegraph Sub-
scriber Exchanges
The most intense sources of radio interference in TV-39 exchanges
are the telegraph relays. Hence, panels for line-balancing unite and sub-
scriber panels contain filters f?~r suppression of interference caused by
telegraph keying. Connection of these filters to the relay circuits is
achieved by means of ,fumpers on the Y11ter housings.
In cites With cable telegraph facilities the measures adopted for
suppression of interference at TV-39 exchanges insure compliance with
item 9d of the standards.
In cities with open-wire telegraph systems residual interference must
meet the requirements of item 9n of the standards. Hence, additional meas-
ures are needed to reduce the voltage level of interference in calling,
connecting, and clearing. It is recommended that the microiilter line and
that a 1-microfarad blocking capacitor be inserted in the d-c supply line
Sanitized Copy Approved for Release 2011/04/01 :CIA-RDP81-002808000100060032-3
 C ~
FIGURE I
Cep~Q/idd (type KpCI) efeetrc~rngnet
C} ~Qf~fd hype K8G-Iltl)
FIGURE 2
~sP "1x1 ohms laomeln)
Cep wQl ?fd (type KBGI)
~"Q05 fr.fd (type KI)Gf)
(~'~QQf uf0 (type KEPI
FIGt1RE 3
C! ~OA23?f
(type K8P)
l~,?O,Smh C~ O,Df~xtd
l:'IGI]R?
6
Sanitized Copy Approved for Release 2011/04/01 :CIA-RDP81-002808000100060032-3