PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR POLYTECHNIC
INSTITUTE named after S. M. KIROV

Vol. 105　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1960

PHASE-MEASURING EQUIPMENT FOR METEOR RESEARCH

I. D. ZOLOTAREV

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

Measuring the path difference between signals of meteor radio reflections received on spaced antennas makes it possible to determine certain essential characteristics of a meteor [4]. Since the path difference between signals received on spaced antennas is proportional to the phase difference between them, measurement of the path difference can be performed with the aid of multichannel phase-measuring devices.

The set of the following initial requirements, which proved decisive in the development of the phase meters, caused serious difficulties in their practical implementation.

1. It is necessary to provide measurement of the phase shift between the high-frequency fillings of short signal pulses (signal-pulse duration \(\tau = 5\ \mu\text{s}\)).

2. The signals received on the spaced antennas are comparable with noise (for an average recorded signal the ratio \(\dfrac{\text{signal}}{\text{noise}} \simeq 3\)).

3. For reliable determination of the phase difference it is necessary to provide a sufficiently large number of periods of the high-frequency filling of the signal pulses. Experience has established that a quite reliable determination of the phase difference can be obtained already with ten periods of the high-frequency filling in the pulse, which, for a signal-pulse duration \(\tau = 5\ \mu\text{s}\), corresponds to an r.f. filling frequency of \(2\ \text{MHz}\).

Consequently, the selected phase-meter circuit must have a sufficiently high (of the order of megahertz) upper limit of operating frequencies.

1. To increase the accuracy of determining the path difference with the same instrumental accuracy of the phase meter, a vernier method of measuring the phase shift was used, employing a two-baseline antenna system.

The selected baseline values were: small baseline — \(a_m = \dfrac{\lambda}{2} = 5\ \text{m}\),

large baseline — \(a_b = 12\lambda = 120\ \text{m}\), where \(\lambda\) is the wavelength.

From the selected value of the small baseline it follows that the phase meter must ensure an unambiguous measurement of the phase difference within the limits \(0 \div 2\pi\).

1. The amplitude level of the signal may vary over wide limits and undergo substantial fluctuations even when reflected from one and the same meteor trail. In addition, because it is fundamentally impossible to make either identical antennas or identical operating conditions for them, the amplitudes of the signals received by each of the spaced antennas may differ in magnitude.

Hence the readings of the phase meter must not depend on changes in the amplitudes of the received signals.

1. In order to accumulate scientific documentation for subsequent processing, it is necessary, taking into account the short lifetime of a meteor, to provide for photographing the screens of the phase-meter indicators.

Below we consider two successive developments of multichannel phase-measuring devices that ensured measurement of the phase shift between the high-frequency fillings of signal pulses under the stated conditions.

Multichannel phase-measuring device implementing the method of measuring phase difference with circular sweep

From the analysis carried out of methods for measuring phase difference, and from experimental work in developing the circuit of the phase-measuring device, the method with circular sweep was selected¹. To ensure an accuracy in measuring the phase shift of the order of \(3^\circ\), a special shaping circuit was developed that produced pulses of duration on the order of \(10^{-8}\) sec, at a repetition frequency of \(2 \cdot 10^6\) pulses/sec. Tests of the operation of the phase meter with circular sweep gave quite satisfactory results, as set forth in [1].

The total duration of the action of the phase-mark pulses on the modulating electrode of the cathode-ray tube (CRT) of the phase-meter indicator, with an exposure of a meteor reflection of 1 sec, will be approximately 0.1 msec, which, in the case of using ordinary CRTs, cannot provide sufficient brightness of the phase marks either for photographic or for visual registration of meteor reflections. Therefore, high-voltage cathode-ray tubes 13LO7A with increased spot brightness are used in the phase-meter indicators. Owing to the low deflection sensitivity of the 13LO7A tubes, powerful sweep devices were developed, correspondingly also consuming large powers from the phase-meter power supply. In addition, the circuit for shaping short pulses of high repetition frequency, in which powerful GU-29 tubes are used for generating the pulses, also requires high-power power supplies.

With a large number of independent channels, the above circumstances very substantially affected the design of the phase-measuring device and the total power consumed by it, which amounted to approximately 10 kW.

The multichannel phase meter includes:

1. An antenna system consisting of six antennas spaced in the north–south and east–west directions—three antennas (\(A_1\), \(A_2\), and \(A_3\)) of the small base and three antennas (\(A_4\), \(A_5\), and \(A_6\)) of the large base.

1. Antenna attachments that make it possible to improve the quality of antenna tuning and to reduce the harmful effect of losses in the cable connecting the antennas with the receiving devices.

2. A cabinet housing the main apparatus, consisting of two three-channel phase meters made identically, and auxiliary units. Each of the three-channel phase meters provides measurement of the phase shift between signals received by the antennas of the small and large bases, respectively.

A simplified block diagram of the phase-measuring device is shown in Fig. 1. The interaction of the elements of the phase meter block diagram is as follows.

Fig. 1. Block diagram of the phase-measuring device.

Signals from the antennas arrive directly at the antenna attachments, from which they are fed by cables to the inputs of the receiving devices. The phase shifts between the signals received on the spaced antennas are measured relative to the phase angles of the “reference” signals received by the reference antennas of the small and large bases.

In the receiving devices, the “reference” channel is split into the actual “reference” channel, the signal voltage from which is used to form pulses of the “reference” phase mark, and the sweep channel, the voltage from which is used to start the sweeps in the phase markers. After amplification and conversion, the voltages of the signals at a frequency of 2 MHz are fed from the outputs of the receiving devices to the inputs of the shaping units, where short phase-mark pulses are formed from them. The voltages obtained from the outputs of the shaping units are fed to the inputs of the markers, each of which contains three phase-meter indicators. Two of them are intended for reading phase differences \(\varphi_1\) and \(\varphi_2\) (the phase difference \(\varphi_1\) is determined between the signals received by antennas spaced in the north–south direction; \(\varphi_2\), between signals received by antennas spaced in the east–west direction); the third—a three-dimensional marker—allows both phase angles to be read as a function of slant range. This makes it possible to distinguish signals from several meteors existing simultaneously at different slant ranges.

The calibrator is the synchronizing unit of the multichannel phase-measuring device and ensures operation of the cabinet in three modes: a) continuous-operation mode; b) intermittent-opeರ-

operation and periodic calibration; c) continuous-calibration mode.

In addition, the calibrator is the principal link between the other station cabinets and the phasemeter cabinet. The following voltages are fed to the calibrator input.

1. From the range-finder cabinet—pulses for starting the range sweep of the three-dimensional indicator, whose repetition rate is \(300\) pulses/sec; and a strobe for blanking the receiving devices during emission of the sounding pulse by the transmitting device.

2. From the transmitter—an unsaturated signal at a frequency of \(30\) MHz, from which the radio pulses for calibration are formed. These radio pulses are radiated by an antenna installed at a selected point of the range, thereby checking the operation of the entire path of each of the phasemeter channels.

3. From the receiving devices of the phasemeter, voltages obtained by converting the voltage from the \(30\)-MHz transmitter to \(2\) MHz are applied to the calibrator. From this voltage, by successive frequency multiplication in the calibrator, a voltage of frequency \(48\) MHz is produced for applying the phase calibration grid to the screens of the phasemeter indicators.

Fig. 2. View of the cabinet of the multichannel phasemeter.

From the output of the calibrator, the voltages are fed to the corresponding units of the cabinet to provide the selected operating modes.

The general view of the cabinet of the multichannel phasemeter is shown in Fig. 2.

Improved phasometric equipment for investigating meteor trails

During operation of the first model of the phasometric device, certain shortcomings were revealed, consisting of the following.

1. The complexity of the equipment required the involvement of highly qualified personnel for its operation.

2. Processing the results of observations was made difficult by the need to align a large number of films taken from each of the indicators.

3. The absence of reserve phasometric channels did not ensure sufficient reliability of the equipment.

It was advisable to proceed to the development of new equipment on condition that a new “compact” method for measuring the phase difference be developed, providing measurement of the phase difference within the limits of

0–\(2\pi\) between the high-frequency fillings of short signal pulses comparable with noise.

In this case the relative fluctuations of the signal in amplitude, both in a given channel and between channels, may be considerable.

We chose the principle of double circular sweep. This method provides measurement of the phase difference within the limits \(0–2\pi\) and permits fluctuations of the signal levels at the input of the phasemeter, thereby partially satisfying the requirements set forth \([2, 3, 5]\).

However, we were not aware of any developments of a method for measuring phase shift with double circular sweep that would make it possible to measure the phase angle at high frequencies with a pulsed signal comparable with noise.

Experiments carried out with the developed circuit of a pulsed phasemeter implementing the method of double circular sweep gave good results.

The new development of the phasemeter “channel for recording angles (‘circle’)” contains nine identical phasometric channels; ten receiving devices, one of which is the reference one.

All ten cathode-ray tubes (nine phasemeter indicators and one range indicator) are photographed in a single frame. The clock, date, frame number are photographed in the same frame, and notes on the type of operation are entered. This provides maximum convenience in processing the film and reliability in preserving complete information on the observations carried out.

The reserve phasometric channels provide increased reliability of operation of the “circle.”

A simplified block diagram of the cabinet of the channel for recording angles (one phasometric channel is shown here) is presented in Fig. 3.

Fig. 3. Simplified block diagram of the “circle.” 1 — receiving devices; 2 — phase sweeps; 3 — heterodyne; 4 — cathode-ray tubes of the phasemeter (8LO-29); 5 — cathode-ray tube of the rangefinder (8LO-30); 6 — recording camera KS-50B; 7 — transmitter of calibration signals; 8 — synchronizing unit of the cabinet; 9 — discriminator.

The interaction of the elements of the cabinet block diagram is as follows. Signals from the spaced antennas at a frequency of \(30\) MHz arrive at the inputs of the receiving devices \((1, 1\text{-}a)\). The heterodyne voltage (3) at a frequency \(f_{2}=28\) MHz is applied to the buffer stages of all receivers.

From the receiver outputs the intermediate-frequency signal voltage \(f_{\mathrm{pr}}=2\) MHz is applied to the corresponding inputs of the phase sweeps (2), and from the output of the receiving device of the reference channel \((1\text{-}a)\) the voltage is applied to the second inputs of the phasemeter sweeps—

...meters connected in parallel¹. From the scanning devices the deflecting voltages are fed to the plates of the cathode-ray tubes of the phase meters (4).

The sync unit of the “angle-registration channel” cabinet (8) ensures synchronous operation of all units of the cabinet, and also serves as the connecting link between the “circle” cabinet and the range cabinet. The inputs of the sync unit receive: 1) range scale marks; 2) pulses for setting the discriminator; 3) a gating pulse; 4) pulses for starting the range sweep; 5) a start pulse (in the presence of meteor echoes) from the “circle” discriminator or from the range-finder discriminator; 6) signal voltage from the reference receiver, from which illumination pulses and discriminator start pulses are generated.

In the sync unit the following voltages are generated: 1) for starting the motion-picture camera (7); 2) for starting the calibration transmitter (6); 3) pulses gating the heterodyne (3) and the cathode-ray tubes (4, 5) during the emission of probing pulses by the transmitting devices; 4) signal-illumination voltage fed to the modulating electrodes of the tubes (4, 5); 5) range-sweep voltage, which is applied to the deflecting plates of the range tube (5); 6) signal and scale-mark voltage fed to the central deflecting electrode of the range tube (5); 7) voltage for checking and adjusting the discriminator (9).

Structurally, the cabinet is made in the form of two racks, in which are placed: 1) a marker unit, where ten cathode-ray tubes are mounted, an insert with clocks, a calendar, and a frame counter; 2) a chassis of nine phase sweeps with vertically arranged mounting; 3) a sync unit, whose mounting is also placed on a vertical panel; 4) receiving devices, located under the cabinet tables; 5) power-supply units, located in the lower part of the cabinet.

The cabinet provides easy access to any elements of the circuit. All identical units of the cabinet are made interchangeable.

Switching on the corresponding elements of the cabinet is carried out by toggle switches located under the cover on the cabinet control panel. The total power consumed by the cabinet is 1 kW, as compared with 10 kW consumed by the first phase-measuring device. The appearance of the cabinet is shown in Fig. 4.

Fig. 4. General view of the “circle” cabinet.

The first tests of the cabinet, conducted on the Lyrid stream during the period April 22–24, 1959, showed that with considerably simpler and more convenient operation, but

increased reliability of operation, low power consumption, and a substantial simplification of observational processing, the new phase-measuring equipment is not inferior in operating quality to the previous development.

A photograph from the indicator screens, obtained during the Perseid stream in 1959, is shown in Fig. 5.

Fig. 5. Photograph of a signal from a meteor, obtained on the “circle” during observations of the Perseid meteor stream on August 13, 1959.

The distribution of phase marks among the antennas is indicated in the light rectangle above the clock. The phase-difference reading is made from the inclination of the major axis of the ellipse. The range marker is located in the lower right corner.

At present, the angular-registration-channel cabinet is in operation and provides recording, on average, of about 500 meteors per day of observations.

REFERENCES

1. Zolotarev I. D., Denisov V. P. Measurement of the phase difference in a pulsed method of circular sweep. The article is included in this collection.

2. Shchegolev E. Ya. On phase differences in periodic processes with rational frequency ratios and on measuring them by means of a cathode oscillograph. ZhTF, vol. IV, issue 1, 1934.

3. Valikhan L. A. Development of the technique of phase measurements (review), issue 2, NTOOI NII, 1958.

4. Robertson D. S., Liddy D. T., Elford W. G. Measurements of winds in the upper atmosphere by means of drifting meteor trails. I–II. J. Atm. Terr. Phys., Nos. 4–5, 1954.

5. Sonon H. Cathode-ray-tube protractor or sinchroscope, Electrical Engineering, vol. 73, No. 3, 1954.

1. By the time the “circle” was put into operation, a transition had been made to operation from a common reference antenna for the small and large bases. ↩↩