SU112389A1 - Synchronization method of receiving and transmitting equipment of devices for oscillographic study of frequency characteristics of long-distance television highways - Google Patents

Description

In devices for studying the frequency characteristics of long-distance coaxial television highways, where the generator of modulated oscillations and the oscillographic parts of the device are geographically disconnected and located at opposite ends of the main line, the possibility of using one common master oscillator is excluded. To ensure synchronous operation of the receiving and transmitting parts of the complex, synchronization methods are usually used, based either on the selection of a narrow-band filter from the frequency-modulated (pm) signal passing the test path to a certain part of its spectrum, followed by detection and generation of a clock pulse, or in the line between the parcels of the PM of the signal of a special video sync pulse to the line.

The disadvantages of the applied methods include the fact that in an unconfigured line, which can in this case have any form of frequency response, the conditions for satisfactory reproduction of a special video clock pulse and, consequently, for its formation from voltage h, m signal.

At the same time, the possibility of the appearance of parasitic, practically unavoidable impulses that violate the synchronous operation of the device is not excluded.

These circumstances lead to a significant complication of the device, caused by the desire to ensure its stable operation, regardless of the primary form of the frequency response of the line.

The proposed method of synchronization of the oscillographic (receiving) part sweep generator is free from the indicated drawbacks and ensures stable synchronization almost independently of the shape of the frequency response of the antenna.

As is well known, with a deliberately slow change in the frequency of the NM signal and low deviacin compared to the bandwidth of the circuit, its static and dynamic frequency characteristics almost completely coincide. In the same case, when the frequency deviation is commensurate or exceeds the bandwidth of the circuit, the static and dynamic characteristics, as the bandwidth of the circuit decreases, begin to differ more and more from each other. Therefore, with the proper choice of the bandwidth of the quadrupole at its output, it is possible to get h. M. signal with significant attenuation. The determination of the magnitude of the attenuation can be approximated by form:

/

/WITH,

where: / Ci is the ratio of the input voltage of the quadrupole to the output voltage in the steady state;

D - quadrupole bandwidth; t is the time of change in the frequency of the PM of the signal within the bandwidth of the quadrupole. For example, when changing the frequency of the PM of the signal sent to the line, from 100 kHz to 12 MHz (11.9 10 yy {), the frequency of the H.M parcels. signal I Hz (T 1 sec.), the quadrupole bandwidth. 1 kHz and its transmission ratio in the established mode, equal to one, the magnitude of the attenuation will be equal to:

I oh

f. -fC I r - (1 r J

AiTA / - 1-76-10-6. 103 (, T)

where

If under these conditions during the absence of h. M. signal, i.e. during the return stroke modular, to her. "PI / 1Y, give a sine wave

sending at the resonant frequency of a quadrupole with a duration of more than 1000 microseconds, then according to the above expression, the amplitude of this signal will be reproduced: in full.

In this way, a similar narrowband quadrupole, in which the simplest quartz fi can be used, reproduces at its output the full amplitude of the sinusoidal pulse (rado-pulse), will significantly weaken the amplitude of the pm signal within the band. transmission of the quadrupole and completely suppress the PM. signal outside the limits of its bandwidth. Due to the significant difference in the amplitudes of the sinusoidal parcel and the PM signal received at the output of the quadrupole, it is possible with the aid of the elementary limiter to single out one sinusoidal parcel and, after detecting some formation, successfully use it to synchronize the sweep of the oscilloscope.

The great advantage of this method of synchronization is that, in order to ensure reliable operation, a line, rather than a completely wide enough range of frequencies, must pass only one sinusoidal frequency. parcels Therefore, if the synchronization channel has very simple narrow-band amplifiers with a gain exceeding the possible attenuation limits introduced by a line at this frequency, the operation of the instrument ceases to depend on the shape of the frequency response of the line.

Thus, the proposed method of providing synchronous operation of the receiving and transmitting parts of the device for studying the frequency characteristics of long-distance coaxial television backbones, while greatly simplifying the synchronization devices, ensures stable and reliable operation regardless of the form of the frequency and characteristics of the investigated and tuned magic. Subject of the method of synchronization of receiving and transmitting equipment of devices for oscillographic 11 investigation of the frequency characteristics of long-distance television backbones, characterized in that, in order to provide a stable sync number 112389 of synchronization, independent of the form of the frequency characteristic of the test highway, radio pulses sent to the line during breaks between the signals of the frequency modulated signal to synchronize the oscilloscope sweep generator, are allocated to the receiver part using w; bandpass filter.