INTELLIGENCE AGENCY REPO INFORMATION P OM a SUBJECT Scl*utifia - IIOctzvn c$ HOW PUBUSHEO MmthlY DpilOdi-O -' WHERE PUBLISHED ?b"cov Axoag the assignments which can be carried out by radio amateurs during the observation of sita+ls from the artificial Earth satellite is the determination of the instant when the satellite viii pass over as observation point. The instant of transit can be determined by various methods, in particular, by the shift cf the received frequency due to Doppler effect, or else by the .etbod of equisignal sons (widely used in radar for determination of angle ecordimates). This article describes the equisignal-tone method and a simple adapter for observations of the satel- lite by this method. The Dquisignal Zone Method What an equisignal zone is can be seen from Figure I. This figure shove schematically two identical antennas, Al and A2, which are located some distance from each other. Radiation patterns of the antennas in the vertical plane are shown here by a solid line. For observations by this method, the radiation patterns of the antennas are formed in such a member that the direction of best reception of the antennas is somewhat displaced in space. Let us assume that the satellite is passing over the antennas in such a vsy as to occupy positions one and two successively. Let us observe the changes of the sig-a1 ^tength in the antennas during the movement of the satellite. As is seen from Figure one, when the satellite is located at position owe the signal in antenna Al viii be at its maxisaa and will considerably ex- ceed the amplitude of the signal in a.nt!ana A2. As the satellite moves to the right from point 1, the signal level increases in antenna A2 and de- creases in antenna Al. Therefore, in position two, which the satellite will occupy i-veral instants later, the signal amplitude in the antennas will not differ as such as.lt did in position one. in its further movwment, the satellite will occupy position three, when the signal becomes equal in both antennas. In this case we can say that the satellite is located in the equisigne.l zone. In space, this zone comprises a vertical plane between the antennas, which the satellite should necessarily intersect when passing over the point of observation, except when the trajectory of the satellite is par- allel to the equisignel plane. Registering the instant of transit of the satailite over the equisignel plane can serve for the precise determina- tion of its orbit. For a determination of this instant both cntenn.s (Al and A2) are caenected to the receiver through a special direction-finding adapter, the basic element of which is an electronic switch. The switch alternately coweets the antennas to the receiver at a rate of several hun- dred times per second (Figure 2), which affords opportunity to observe the oscillations at the output of the receiver (Figure 3) to determine the ratio of the signals induced in antennas Al and A2. If the.satellits is outside the equisigml zone, then the signal strength in.tbe two antennas is different; therefore, the amplitude of the oscillations 1t the input of the receiver changes with the frequency of the sa?~naa snitching (Figure 3)? Detection of these oeclllatlons gill produce square pulses, reproducing the signal envelope at the input of the receiver. These pulses can be heard as n tone with a frequency equal to that of the antenna snitching (with local oscillator disconnected). In the course of and the movement of the satellite, the niggnaltineantenna Al vill decrease wind at the will increase in antenna A2; am & decrease. At the Instant the satelli e transits the uutsoignaal zoos, tc the htb* ll Al and ea will eq., and the tong an equisignal planes in antennas ng frequency will not be heard (Figure 3). ToAec the antennas should be completely identical and have symmetrical (with f respect to the verti'al axis) radiation f. The hertl uired shcanift of the direction of pens. ing with threspect to the eaantennes. attained by a proper position The basic element of the described )itecth controls two it rtr (Fiiggure 4) Is a symmetrical sultlvibrator (L4,lfj high-frequency amplifiers (L1,L2) with a common plate load (circuits IQ, C5,C6 . The signal from each rntenns is transmitted to the corresponding input (Al A2) of the amplifier by means of a coaxial cable. To the screen grids of tubes L1 and IQ is supplied a voltage in the fora of square pulses, which change the potential of the screen grids in steps from 0 to 4120 volts. Ir accordance with there occurs n~l- ternate connection of the bigb-frequency amplification adapter (ges , and from eoemon plate load to the output stage fled signals alternate from each of the antennas. The sultivibretar, built with an electron coupled c 1c cuQtt, generates rmined b pulses which are almost square. The switching frequency oi rdtresistor-9 the capacitance of the capacitors C77, Cg and Rio. For the magnitudes of the" eleeenta in this circuit, the switch ng frequency is 270 cycles. For the complete cutoff of tubes I,e 2f small positive (with respect to the catsodea of tubes 4,, volta is buabttry 10 volts is applied to the cathodes of tubes L1 L2, by the current in the circuits of the cathodes of tubes LI, L2, L3 actors the resistor R5. Autotranaformers are used to match the characteristic impedance of the cable (75 ohms) at the input circuits. The cathode circuit of the output stage, which comprises a cocoon cathode follower, is closei on the direct current through the incoming circuit of the receiver. - method, it is necessary that For observation by the vent al s~ amplification. Adjustment of both high-iregwncy stages have the e same .mop amplification is accomplished by changing the bias at the grids of tubes LI, I2 with the _id of resistor R3. The capacitors C and CIO, each 100 alcromicrofareds, decocq?le the screen grids of the higfl-frequeo Y amplifier tubes and do not affect the form of switching voltage. The adapter is installed close to the antennas; therefore, a low voltage of 12.6 volts is selected for its power supply. This voltage is supplied directly to the beating circuits of the tubes, divided into two'seri a-conxcted groups. The aiddla point of the primary winding of the power transformer is grounded and serves to equalise the heater voltage (6.3 volts) in both groups. For power supply to plate cir_uits, a common KeD trop rectifier 67e`;S (L6) is used. A potential of 12.6 volts is obtained from a special traneforewar installed in the vicinity of the receiver; this transformer ccc?allf has to be designed for a potential of 13-14 volts to coepeneata for the potential drop in the connecting wire. Structurally, this direction-finding adapter is built on a seprrata clsusais having the dimensions 190 by 150 by 60 sm. The location of the tantc components on the chassis is seen in Figure 5. r' duce the mutual effect of stegee, copper, brass, or aluminum screening sections (tubs shields) are placed between tubes L1, 12 and I.. On the side of the c.`.Ass is are three t.rrctnal'bloeks for coaxial able (two for antennas Al and A2 and one for the connection to the receiver). Miring of both stages of high frequency amplification should be carried out according to the same wiring system. ibe grounding of all components belonging to the ease stage in done at one point near the corresponding tube. Trimming capacitors Cl, C5 and CI2 are mounted in such a Penner that the tuning of the circuits can be achie ed without rettaving the lower lid of the dlrectioh-finding adapter. Pugh-frequency coils L1, I.2, L3 are mounted at the output of the corresponding trimming capacitors. These coils are made with silvered wire with a diameter from one to 1-1/2 mm, wound on an 8-em mandrel, and cortaining seven turns. After winding, the coil is stretched to a length of 18 sm. Coils LI and L3 have tape fro^ the second turn, counting frost the grounded end. Trl has a core of plates Sh-19 (thickness of the assembly, 20 ass). NiMtng oo, has 2 by 110 turns of P EL-1 wire, 0.74, three secondary- 11- 2 by 4,900 turns of PSL-1, wire, 0.12. The choke of ftlter_Arl ban a core of Sh-15 plates, having an assembly thickneas of 25 m. The winding is dcos with P14 -i wire, 0.15, covering the vtote form. A step-down transformer for the power supply to the adapter (rot indicated in the figure) is built with a core of Sh-19 plates; the thickness of the aaaembly is 50 ma. The priPary winding of this trsasformer to d-algned for conre'ttoa to a power line of 110, 127, and 220 volts %M coTitalna, accordingly, 550 turns plus 83 turns of PEL-1 wire, 0.44, 4 470 turns of PrL-1, wire 0.33. The step-down winding consists of 87 turns at Fly.-l wire, 1.2, and bas tape from the 72d, 77th, and 82d turns for selac- tton to the adapter of a normal voltage of 12.6 volts. Between the pri- nary and the secondary winding is a screen made of a single layer of PEL-1 vl:ea, 0.15 to 0.2. Adjusting to the direction finding adapter Is usually begun by check- li,g tube performance. The operation of the multivibrator is checked with the aid or an oacillograph; the pulses should he practically square at the plates of tubes lt? L5. When there is a considerable difference in the duration cf the two belt-periods of the generated oscillations, it is necessary to change sacvbat the value of leek resistance or .be capacitance of the separatloa capacitor in the circuit of the control grid of one of the tubes. It I. desirable to check the frequency of the aultivibrator- generated oscillations with the aid of an audiogeneretor (with respect to ISssajoua figures on the screen of the oecilingraph). If it is necessary, the frequency can be changed by the selection of capacitors C7, C8 or the resistors R9, R10. For tuning the high-frequency saplifier, generator 80-1 and voltmeter D?:3-7 can be used. For this purpose, a 75-ohm resistance is connected tc porarily at an output of a cathode follower. T"- tuning of each stage of the high-frequency amplifier is repeated cavcral times. The final tuning stage is balanced through a balancing and equalisipg of the amplification of both arms of the amplifier (with the aid of R3). Antennas Stall-wave split dipoles, similar to those which are used for the reception of TV programs, can be used as the antennas. To secure the desired direction for the best reception, the antennas should be placed at a height of a quarter of a wave above the earth's surface. In contrast to television reception, the diameter of the dipoles can be .elected only on the basis of constructional considerations} the antenna band-width is of no significance. The antenna structure should be sufficiently rigid so that it will not be swayed by a strong wind. For measurements by the equisignal zone method, two identical dipoles are used, placed exactly parallel to each other at a distance of the order of half a wave length. (In the future, this distance will be more accu- rately defined.) The dipoles are oriented (ane Figure 8) so that the line connecting their centers will coincide with the east-vest direction and so that the equisignal plane is in the direction of the meridian. The dirrction- finding adapter is installed on the ground between the antennas, is covered with a protecting jacket, and is connected to the antennas by cables of equal length (with an accuracy up to one to 2 cm). Becaure the earth's surface participates forming the antenna radia- tion pattern, the antenna should be located on a level site; any consider- able unevenness of the relief at the site of the antenna will distort the egida iinal zone and will cause errors in observations. For the same rea- son, for a distance of up to ten vayelengths, there should not be any large metallic masses and other shielding objects. It is also objection- able to use metal guy rods for fastening the_antennaa. As already men- tioned, using the equisignal method is impractical in cities. The con- struction of one of the possible antenna variants for a wave length of 7.5 meters (40 megacycles) is shown in Figure 7. Coupling the antenna to an unbalanced 75-ohm coaxial cable is done with the aid of a balancing U-shaped bred. The dipoles are located at a height of 18.75 meters above the earth's surface, and the distance between then is 3.75 asters. The radiation pattern of a single antenna for this particular we is shown. in Figure 9. For operations without the switch, one of the antennas is directly connected to the input of the receiver. (Appended figures follow.) OLt Figuxe 2.. ~y ~? d gRl~;b L~066 prSR if e It: R1)1r. 1fai Cj .(C ,rn, fm - t.l `? 1U.1tN C?4?a 1 i FA 0 HRn0 s,crl w,f. IS L56F6a Figure 4 .-W 1662'SW t" 2I Bolder the able cable rk-lo rk-3, rk-49

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