PHOTOGRAPHIC RECORDING OF SIGNALS FROM AN ARTIFICIAL EARTH SATELLITE ON CONTINUOUSLY MOVING PHOTOGRAPHIC FILM

I. Sh. SOLOMONIK

(Presented by the scientific seminar of the Radio Engineering Faculty)

At present, as far as we know, the recording of signals from an artificial Earth satellite is carried out on magnetic tape by means of a tape recorder connected to the output device of the receiver. In this process the signal level, the signal shape, and the difference frequencies caused by the Doppler effect are recorded.

Despite the apparent simplicity of the generally accepted method of magnetic-tape recording of AES signals, this method has a number of shortcomings, of which the principal ones should be considered:

1) the great complexity of the operations involved in decoding the information obtained from radio observations;

2) the large consumption of materials—magnetic tape (about 150 meters for one observation);

3) the difficulty of selecting the most interesting sections of the recording;

4) the difficulty of forwarding, storing, and processing observational materials at information-collection points.

To eliminate the indicated shortcomings, it is proposed to photograph the signals on continuously drawn motion-picture film of standard dimensions with the aid of special apparatus, the block diagram of which is shown in Fig. 1.

Below is given a brief description of the elements included in the block diagram of the proposed apparatus.

Fig. 1. Block diagram of an installation for photographic recording of AES signals: 1—radio receiving device; 2—oscillographic device; 3—frequency counter; 4—device for illuminating the clock; 5—photoadapter; 6—indicator of the level of attenuation of AES signals.

1. A radio receiving device with an automatic gain control system—AGC.

2. An oscillographic device consisting of an amplifier for horizontal deflection of the signal under study and the power-supply circuits of the tube. The vertical sweep of the signal is carried out by mechanical drawing of the photographic film at a speed of 2 mm per sec; then during one observa-

... lasting approximately 10 minutes, about 1.2 m of motion-picture film is used. The resolving power of the photographic film and of the lens of the photographic attachment of the “Industar-22” type fully ensures clear separation of the intervals and of the coded signal transmissions of the AES.

1. A counter–frequency meter with a decade readout device for thousands, hundreds, tens, and units of hertz. Neon bulbs are used as indicator cells. For photographic recording of the Doppler effect of AES signals by the proposed method, the neon bulbs of the decades must be arranged linearly in a direction perpendicular to the direction of advance of the photographic film. Then, when photographing on continuously moving motion-picture film, streaks will be obtained from the lit neon bulbs.

2. A device for illuminating the hands of the clock–stopwatch. For illumination of the hands it is advisable to use neon bulbs, lit once every 3 sec. The duration of the illumination is 0.1 sec. With continuous advance of the photographic film, streaks of the second and minute hands will be obtained on it at various angles to the horizontal, in accordance with the time reading, without appreciable velocity smearing of the image of the hands.

3. The photographic attachment consists of the simplest optical system and a motion-picture film transport mechanism. As the photographic film it is advisable to use high-sensitivity film of the RF-3 type.

4. A device for indicating the attenuation level of AES signals. The need for such a device is caused by the following circumstance. The level of AES signals in the reception zone varies over wide limits, and, because of the limiting effect, distortion of the envelope shape of the signal may occur. It is therefore advisable to provide the receiving device with automatic gain control—AGC.

The output voltage of the AGC should be fed either to an optical indicator, whose darkening sector must be calibrated in advance, or to another device for indicating the attenuation level. As such a device one may use an oscilloscope consisting of a direct-current amplifier for horizontal deflection of the spot of the cathode-ray tube and the tube’s power-supply circuits. In this case the magnitude of the spot deflection will depend on the level of the signal taken from the AGC. With a sufficiently large time constant of the AGC, an inclined line will be obtained on the moving photographic film. From the magnitude of the deflection of each point of this line from the position of the point corresponding to the absence of an AGC signal, one can judge the attenuation level of the signals received by the AGC system (section 3, Fig. 2). To reduce the error in reading the attenuation level that arises from mechanical displacement of the film during advance, it is advisable to provide for photographing neon bulbs forming a grid—a scale of attenuations (1; 5; 10; 20 times).

Thus, by photographing on the photographic film the darkening sector of the optical indicator or the position of the spot of the cathode-ray tube of the attenuation-level indication device, one can determine the magnitude of the attenuation of the AES signal; this, in turn, will make it possible to calculate the actual level of the AES signal at each instant of time.

The scheme for recording AES signals on motion-picture film is shown in Fig. 2.

In this figure are marked the sections of recording on the photographic film (with the film moving from top to bottom): the hands of the clock–stopwatch—section I; the magnitude of the Doppler effect—section II; the attenuation level—section III; and the level and shape of the received signal—section IV. Examples of readings are illustrated in the same figure.

Report 1

I — time . . . . . . . . 0 min. 3 sec.
II — frequency . . . . . \(3 \cdot 10^{3} + 0 \cdot 10^{2} + 2 \cdot 10^{1} + 3 \cdot 10^{0} = 3023\) cps.
III — attenuation . . . \(\simeq 4\) times.
IV — form—pause (duration—0.5 sec).

Report 2

I — time . . . . . . . . 0 min. 15 sec.
II — frequency . . . . . \(3 \cdot 10^{3} + 0 \cdot 10^{2} + 9 \cdot 10^{1} + 4 \cdot 10^{0} = 3094\) cps.
III — attenuation . . . \(\simeq 7\) times.
IV — form—burst (duration—0.3 sec).

Labels in the figure: portions of photoregistration on a section of motion-picture film; I; II; III; IV; direction of film movement; 0.3 sec; 0.5 sec; 2nd report; 1st report; \(\simeq 7\); \(\simeq 4\); clock; frequency counter; \(20\ 10\ 5\ 1\); \(\times 10^{3}\); \(\times 10^{2}\); \(\times 10^{1}\); \(\times 1\); 24; oscilloscope; atten.; form; objects of photography; photography.

Fig. 2. Diagram of the recording of AES signals on motion-picture film.

Consequently, as a result of implementing the indicated method of recording AES signals, the complications in processing the portions of information of interest to us are completely eliminated; the necessity of storing and subsequently processing a large amount of magnetic tape is eliminated; and, consequently, a certain economic effect is expected, since the network of observation stations is extremely extensive, while the costs of implementing the method are small.