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Approved For Release 2000/08/29 : CIA-RDP78-04861A00000'56Ob3-3 Translated from: ELEKTRICHESTVO NO. 7 1952 pp. 41-46 Lo .-ran.e H.F Telephonic Communication over Power Transmission Lines by Cands, Tech. Sci. I.K. BOBROVSKAYA, Ya,L. BI HQ'MKY, K.P. XEEGDROV and Engineers V.I. iiMDVEDEV and N.G. ivY'AKOCEENA (41aJ Consideration of the fundamental data of the EPO-~ apparatus, dcsig=d fox the ura off' H.P. Tblophany' chamcls along eiocts l transmi3sion lines. The method of single sideband transmission used in the apparatus and a number of other refinements permit a considerable increase in the range of H.F. colivaunicat ions reliability and capacity (degree of use7of high voltage lines for telephonic purposes. ] trodu U.q In 1922 J oade 'ua A.A. CHERT SHEV carried out H.F. telephonic cannunication over the 110KV tr~n~ lire fx K&SM to W=W. Later thanks to the work of V.A. D'YAKOV, A.M. MuizhKOV, V.1. IVANOV, M.P. PAP TIN and a number of other Soviet scientists and engineers this fox m of ccex .uxiicat i o . beoema the most aVortan. - means * siowl ipg. ~D I ?SKIIYE , UPRAVLETNIYE7 on power systems. The soviet apparatus type DPK, which works by transmitting currents at carrier frequency to line with two side bands and transrt.tter per of 5 watts on telephony, has been most widely used. The rapid growth of power systems in the postwar period, the increase in distances over which electrical power is transmitted and the necessity f, 'pr a considerable increase in the number of channels for both telephony and remote- control rtelemechanios 7 and protection, all demanded the development of new types of H.P. apparatus. This :-work was initiated by the communications laboratory of TSNIEL .- S in 1945.1i0asle of terminal apparatus for telephonic channels were worked out by the factory of the .1inistry of the Cow.iunications Apparatus Industry in co-operation with the chair of long-distance communications of the Electroteehnical Institute of Cow iunications i./n. BONCH-BRUYEVICH with participation by TSNIT';L. The new apparatus was allotted the designation EPO-1 Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 (communications over electrical transmission lanes) single sideband, one telephonic channel /1EKL'ROPEREDt.CH1. ODNdOPOLOSNLYL 7). Conditions for Communications over Electrical Transmission Lines For long distance communications over 110 or 220KV electrical trans- mission lines currents are used with frequencies from 50 to 300 Kc/s Transition [PKREKHODIM, J attenuations between individual transmission (?average) lines carrying H.F. currents are not large. For lines leaving a general substation with the apparatus connected according to the phase-earth method, the transition attenuation is about 2 rep. In view of this, for communications over different lines it is necessary to use different frequency bands; duplication [repetition) of frequencies on the lines of a single power system is admissible only in exceptional cases. Catering for all the growing demands of power systems for channels for telephonic comzunication, protection and remote control is possible only if 1G2 the most economical use is made of the frequency spectrum. This consideration is of the greatest importance in planning coimnunication over electrical transmission lines. A second and no less material feature of electrical transmission lines considered as lines of congnunioation is the extremely high interference level due to corona effect, discharge at insulators and various transition fPER KHODNYJ processes. On '_10KV lines the interference level in a band 2.5 Kcls wide is -4.85 nep., and for 220KV lines, -2.85 nep. Present day communications technique has many methods of modulation and detection. The most ecoz deal frequency band, whilst preserving a relatively high degree of freedom from interference is obtained by the method by which current is passed to the line on only one side band in ar_iptitude modulation; the current on the other side band and the carrier current are suppressed in the frequency changer and filters. This method was adopted as the principle in planning the PO-1 apparatus. Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Comparison of the EP0-1 apparatus with sets of types DPK, A.24 and others working on the principle of transmitting the currents of the carrier frequency and both sidebands to line shows that the change to the single sideband system, with the same degree of interference, allows for increase in line attenuation by ,-.05-1.32 nep, corresponding to a gain in transmitter power of 8-14 times (depending on the depth of modulation in the old systems). In Fig. 1. is.shovrn the skeletcn circuit of the H.P. channel. The attenuation on the length of line was determined by the approximate foirnzla. b= llcV; + 0.8n + 0.65 - klk (i) where I is the overall length of the electrical transmission line, in Ion; K = 1.3 x 10"'3 for 110KV lines. and 0.72 x 10-3 for 220 lines; f = frequency in Kc/s; n = number of by pass circuits; lk the overall, length of H.F. cable to the transmitting ten-dnal and in all the by pass circuits (usually about 0.5 Km)13k = damping per km. of cable (from 0.142 to 0.445 nep/km. in the band from 50 to 300 kc/s). For a frequency of 150 Ko/s the attenuation of the H.F. circuit on j2aJ 110KV lines 200 Kn. long with two by pass circuits is about 5.5 nep. and on 220 KV lines 300 Kr_i. long with one by pass circuit, about 4.2 nep. If we take 200 KV lines as a basis, and in accordance with what has been said above regarding interference level, assume this to be 2.85 nep; then satisfying ourselves with a safety margin protection, shieldin,` of 3 nep. (operational tests show that the quality of reception of speech is better at this value), we obtain a transmitting level at the input of the H.F. section equal to + 4.35 nep., which corresponds to a transmitter power with single sideband apparatus of 6 watts. The necessity of working on frequencies up to 300 kc/s forces us to increase the power of the transmitter to 9-10 Mitts. High frequency channels on electric transmission lines should not be put out of adjustuent by damage to the Line. Th ks to the presence between phases of electrataagnetic linkage, the attenuation of the H.F. transmission circuit rtraokJ in most cases of damage increases by 2-3 nep. Since when Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 damage occurs the high voltage is taken off the transmission line and the interference level is considerably reduced, communications can work uninteruptedly,, provided the apparatus is fitted with sufficiently good automatic regulation of amplification. The Frequency band of the Apparatus: The EP0-1 apparatus works on a band of frequencies froze 51 to 303 Kc/s. This range is subdivided into 84 bands, each 3 Kc/s broad. 51-54 Kc/s, 54-57 Kc/s and so on to 300-303 Ke/s. To obtain a two-way telephonic conversation any two bands of 3 Ke/s width can be used provided that they are separated by not less than 12 Kc/s. The tuning of the apparatus is fixed, but provision is made for mutual charges of the positions of the transmitting and receiving frequency bands. The band of frequencies which can be effectively transmitted in the audible TtonaiJ range lies within the limits of from 0.3 to 2.7 Kc/s. The conversion of the speech frequencies takes place in two stages. In the first stage carrier frequencies of 6, 9, 12, 15 Kc/s can be used. As a result of the first conversion the speech frequencies are transferred to the bands 3-6, 6-9, 9-12 and 12-15 Kc/s. By means of a second conversion the speech frequency band is transferred to the position in the frequency spectrum 51-303 Kc/s which it is to occupy on the line. In the second stage of the conversion carrier frequencies r2b7 66, 78, 108, 120, 150, 162, 192, 204, 234, 246, 276 and 288 1Cc/s are used At the output from the converter either the upper or lover side band is removed by the band filter. The choice of nominal carrier frequencies in two stage conversion is made according to what frequency bands are to be used an the line. In the receiving part of the apparatus frequency conversion takes place in the reverse order. The distribution of frequencies of the 12?01 apparatus is given in the table. Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Crystal frequency Channel No. Kc/s 66 1, 2, 3, 4, 7, 8, 9, 10 78 5, 6, 7, 8, 11, 12, 13, 14 108 15, 16, 17, 18, 21, 22, 23, 24 120 19, 20, 21, 22, 25, 26, 27, 28 150 29, 30, 31, 32, 35, 36, 37, 38 162 33, 34, 35, 36, 39, 40, 41, 42 192 43, 44, 45, 46, 49, 50, 51, 52 204 47, 48, 49, 50, 53, 54, 55, 56 234 57, 58, 59, 60 63, 64, 65, 66 246 61, 62, 63, 64, 67, 68, 69, 70 276 719 72, 73, 74, 77, 78, 79, 80 288 75, 76, 77, 78, 81, 82, 83, 84 Note Channel No.1 occupies the band from 51-54 KC/s, channel No.2 frct 54-57 Kc/s &c. up to channel No.84 which occupies the band from 300-303 Kc/s. Standt:rd.isation of the positions of the siaebands limas introduced for the first tine in corriunication over electrical transmission lines. This refinement allows a substantial improvement to be made in the organisation of corrlunications on large power systems. Skeleton Circuit of EPO-1 apparatus ancl transmission and reception levels. The skeleton circuit of the EPO-1 apparatus is shown in Fig. 2. Speech currents passing through the contact of the relay of the automatic selector (AVTOM ATIKAJ and through the 0.4 nep extender (UDLINITEL'J (which is switchecl out with two-wire working (TRANZITJ) reach the first-stage converter i-1.1 through the differential circuit DS. This converter like all the others, is assembled frerl cuprous oxide el ents fKUPROKSYJ in a bridre L riiJ arrangement. Carrier currents of 6, 9, 12 or 15 Kc/s are fed from the harmonic generator GNCh with a fundamental frequency of 3 Kc/s, crystal controlled. Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 To the output of the first converter is connected the band- filter P.F., which removes the lower sidebands, (3-6, 6-9t 9i2; 12-15 Kc/s). The currents separated by the band -filter reach the second stage converter 11 .2 through the intermediate amplifier PUS. Carrier currents are supplied to it fran the crystal generator KG-VCh, tuned to one of the 12 frequencies (see table). Connected to the putput of converter U-2 is the band fi2tor Fper which separates the sideband for transmission to the line. Passing through the filter Fper the currents are amplified by the high power transmitter amplifier i:NS and reach the line via the line filter LF. When a tone frequency of 800 c/s is applied to the input of the apparatus tiAth a level of -1 nep, the level corresponding to the side- band frequency at the input to the line is + 4.6 nep (10 watts). Thanks to thishigh transmission level the difference between the signal level and mean interference level at the receiving end is not less than 3 nep. with attenuation on 2207KV lines of up to 4.45 nop. and on i ,{ t'.linea up to 3aJ 6.45 nep. The minimum reception level can be -3.4 nep., and this ensures, in an emergency, communications over lines with attenuation up to 8 nep. Currents coming in from the line reach the receiving portion of the apparatus through the band filter P.F. and the extender U, the attenuatiaz of which can be regulated between the limits 0-5 nep. in steps of 0.5 nep. By means of the extender U a normal level of reception is established at the input of the controllable artificial line RIL. The total attenuation of the line and extender should be about.6 nep. Fluctuations in line attenuation within the limits of+ 2 nap. are 1 ,j -7 automatically ccalpensated by corresponding changes of the attenuation in RIL which can be regulated by the control current. For the latter, the carrier current from the first-stage converter is used, this being fed from CTCh to the intermediate amplifier PUS and the first converter in parallel. The level of the control current at the input to the line is +3.inep. Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Approved For Release 2000/08/29 : CIA-RDP78-04861A000300050003-3 Autom