SU117821A1 - Method for automatic elimination of long-lasting predominance of signals in the receiver of the equipment of the TT systems with FM - Google Patents

Description

The invention relates to methods for automatically eliminating the long-term predominance of signals in a receiver of voice frequency wiring (CT) with frequency modulation (FM) without changing the phase of the carrier frequency, when the duration of the telegraph messages at the receiving end of the channel remains unchanged and only the amplitude of polar signals changes.

In the known methods of eliminating the prevalence, this is achieved either by using a special control channel, either by fixing the edges of the received pulses as a result of imposing a differentiated signal on the envelope of the signal or by using circuits with peak detectors.

The described method is based on the formation of a reference signal at the receiving end, the duration of which is compared with the duration of the signal at the output of the CT system. In this case, the error signal appearing in the comparison device is used to eliminate the predominance.

The reference signal is formed by pulses obtained by differentiating the telegraph parcels at the output of the amplitude detector of the frequency discriminator, which increases the correcting ability of the receiving equipment.

FIG. Figure 1 shows the voltage shape of the envelope at the output of the amplitude detector; in fig. 2 - a sequence of pulses at the output of the differentiating chain; in fig. 3 - waveform at the output of the forming device; in fig. 4 is a block diagram of a device for automatically eliminating dominance in a CT channel; in fig. 5 is a block diagram of an auxiliary device.

No. 117821-2 -

As follows from FIG. 1, the point of the maximum steepness of the envelopes at the output of the discriminator of an undistorted signal and a signal that prevails predominantly remains constant over time. This dot position is used to obtain reference signals.

FIG. 1 curve abvgdezh corresponds to the envelope of the undistorted signal, and curve ai6iei3i5iei ci - signal with a predominance. Such a position of the points corresponds only when working on the linear part of the characteristics of the discriminator. The prevalence resulting from various causes does not violate this pattern.

If the signal envelope .TT is applied to differentiating chain 2 (Fig. 4), then its output will result in pulses whose position in time will depend only on the change of polarity of the signal and will not depend on the magnitude of the predominance (Fig. 2).

The received pulses (Fig. 2) are fed to a forming device (Fig. 4), at the output of which, in accordance with incoming ones. pulses, signals of one or another polarity appear (Fig. 3). As a forming device, you can use a trigger circuit.

At the output of the shaping device, undistorted reference signals 4 are obtained (Fig. 4). The reference signals are fed to a comparison circuit 5, to the other output of which signals 6 are supplied from the output of the receiver.

In comparison circuit 5, the durations of the respective positive or negative premises of the transmitted combination are compared.

If the duration of all positive (or negative) reference packages is equal to the duration of the corresponding packages received from the channel output, then at the output of the comparison circuit the voltage will be zero. If the duration of the reference pulses is longer than the duration of the distorted packages, then the voltage of one character is. If the duration of the reference parcels is shorter than the duration of the distorted parcels, the voltage of another sign.

At the output of the comparison circuit, a voltage appears that is proportional to the difference in the duration of the reference and distorted packages.

The voltage received at the output of the comparison circuit is used as the control voltage 7. It is fed to the input of the trigger 8, available in the CT receiver, to change the position of its operating point. Thus, automatic elimination of the prevailing prevails.

In order to avoid false overcompensation of the predominance of a long sending of one character, a special auxiliary control circuit 9 is used (Fig. 4 and Fig. 5), the principle of which is as follows.

The voltage at the output of the discriminator / is proportional only to the frequency of the signal supplied to the circuits of the discriminator 10 (Fig. 5).

The alternating voltage at the output of the discriminator, corresponding to the frequency of pressing the positive premise / i or the frequency of pressing, minus premise / 2, is strictly fixed for this discriminator, and therefore the voltage deviation can be taken as a measure of the frequency deviation / 1 or / 2 from the nominal values Ie for a measure of the prevalence of the signal.

When the auxiliary rectifiers // are installed at the output of the discriminator circuits and the circuit is constructed in such a way that the voltage is only output at its output if the rectified voltage after the rectifier differs from the voltage taken as nominal and determined by the frequency fi or / 2, the magnitude and sign of this voltage will characterize the magnitude and sign of predominance with a long press or release.

The time constant of the auxiliary rectifiers must be equal to the time constant of the comparing value of the main circuit and must be large enough for the circuit to work only with long plus or minus messages (frequency fi or).

When a single sign is sent to the output device S for a long time, a control voltage will be supplied from the auxiliary circuit 9, the sign and value of which will depend on the value of the deviated frequency / i or / 2 of the nominal value and which will prepare the output device to receive the first work packages without distortion.

When the operation starts, the control voltage from the main circuit will gradually appear, and the control voltage of the auxiliary circuit will decrease with the same speed.

Thus, the signals of work with a long working parcel and the first signals of work after a long stop or starting pulse will be perceived without distortion.

Constant voltages obtained from batteries 12 (FIG. 5) are necessary in order to make a comparison of the rectified voltage, obtained from the discriminator rectifier, with a reference voltage, which must be equal to the nominal value of the rectified voltage.

Subject invention

Method for automatic elimination of long-lasting predominance of signals in the receiver of the equipment of FM TT systems operating without changing the phase of the carrier frequency, using differentiating, shaping and comparing devices and rectifiers with a common output, characterized in that in order to increase the correcting ability of the receiving equipment of the channels , the predominance determination is made by comparing the signal at the output of the TT channel equipment with the reference signal, which is generated by pulses derived from the differentiation the beating telegraph parcels at the output of the amplitude detector of the frequency discriminator, or by comparing the signal voltage at the common output of two rectifiers included in the outputs of the frequency discriminator circuits with the reference voltage.

№ 117821