SU786054A1 - Facsimile signal transmitting device - Google Patents

Description

(54) DEVICE FOR TRANSFERING FAX SIGNALS

one

The invention relates to video signal circuits of devices for transmitting images and can be used, for example, in facsimile equipment for transmitting images.

Compressions using frequency modulation with a | partial loudspeaker of the upper sideband of the transmitted signal. A device for transmitting facsimile signals containing a photoelectric converter, the output of which is connected to the input of the equalizer and the input of the frequency modulator, is known. The output of the frequency modulator is connected to the input of the first delay line, the output of which is connected to the first input of the multiplier, the input of the first adder, the second input of which is connected to the output of the voltage source, and the output of the first adder is connected to the second input of the multiplier, the output of which is connected to the input First low pass filter 1.

However, in the known device, in spite of the compensation of distortions caused by partial suppression of the upper side band of the spectrum, nonlinear distorted effects occur, which for the signal frequencies close to the difference between the upper limit of the communication channel bandwidth and the sum of the frequencies of the deviation normals are unacceptably large.

The purpose of the invention is to increase the degree of compensation for non-linear distortions of transmitted signals.

For this, a device for transmitting facsimile signals containing a photoelectric converter, the output of which is connected to the equalizer input and the input of the frequency modulator, while the output of the frequency modulator is connected to the input of the first delay line, the output of which is connected to the first input of the multiplier, and the output of the equalizer the first input of the first adder, the second input of which is connected to the output of the voltage source, and the output of the first adder is connected to the second input of the multiplier, the output of which is connected to the input of the first low-pass filter, the second delay line, the second adder, the amplitude limiter and the second low-pass filter are entered, the output of the first delay line is connected to the first input of the second adder via the second delay line, and the output of the first low-pass filter is connected to the second input of the second summatf directly and with the third input of the second adder - through the amplitude limiter, with the output of the second adder connected to the input of the second low-pass filter.

The drawing shows a block diagram of the proposed device.

The device for transmitting facsimile signals contains a photoelectric converter 1, the output of which is connected to the input of the corrector 2 and the input of the frequency modulator 3, the output of which is connected to the input of the first delay line 4, the output of which is connected to the first input of the multiplier 5, adder 6, the reference voltage source 7, the first low-pass filter 8, the second delay line 9, the second adder iO, the amplitude limiter and the second low-pass filter 12.

The proposed J device works as follows.

The output signal of the photoelectric converter 1 controls the frequency modulator 3, from the output of which the frequency-modulated signal after a delay in the first delay line 4 goes to the first input of the multiplier 5 and after a delay in the second delay line 9 to the first input of the adder 10. Together with However, the output signal of the photoelectric converter 1 after linear amplitude but-frequency correction in the corrector 2 is fed to the first input of the adder b, to the second input of which the reference voltage signal comes from the output of the source of supports voltage 7. The signals from the equalizer 2 and from the source of the reference voltage 7 are summed in the adder 6 and fed to the second input. 5. The signals from the output of the first delay line 4 and the adder 6 are multiplied in multiplier 5, where a frequency-modulated signal is formed with a partially suppressed upper side band of the spectrum for frequencies greater than the upper limit of the channel bandwidth M1r4pc and partially compensated for by distortion by this suppression. The signal from the output of the multiplier 5 after the final suppression of the upper sideband in the low-pass filter 8 arrives at the second input of the second adder 10. After the amplitude limit in the amplitude limiter 11 goes to the third input of the second adder 10. At the output of the second adder 10 signal

U, (U ,, - V9) i;

where Ue, U (o, Uii, Ue are the voltage at the output of the corresponding blocks of the device.

which, after suppression in the low-pass filter 12 of its upper sideband for frequencies greater than the upper limit of the channel bandwidth, enters the communication channel.

The reduction of distortions in the proposed device is explained by the fact that at the receiving side, the frequency-modulated signal from the output of the second filter is subjected to amplitude limiting and frequency demodulation after passing the channel

frequency 12 with a partially suppressed upper sideband, since from the output of the second adder 10 a signal from the second lowpass filter 12 receives a signal from the adder 10, which differs from the lowpass filter 8 by a value that determines the distortions amplitude limiting. This value compensates for the same distortion that occurs in antiphase with it when the amplitude limit signal from the output

the second low pass filter 12 at the receiving side.

Claims (1)

The formula invented. A device for transmitting facsimile signals containing a photoelectric converter, the output of which is connected to the equalizer input and the input of the frequency modulator, the output of the frequency modulator connected to the input of the first delay line, the output of which is connected to the first input of the multiplier, and the output of the corrector connected with the first input of the first adder, the second input of which is connected to the output of the voltage source, and the output of the first adder is connected to the second input of the multiplier, whose output is Dinene with the input of the first low-pass filter, characterized in that, in order to increase the degree of compensation of non-linear distortions of the transmitted signals, the second delay line is introduced, the second adder, amplitude limiter and the second low-pass filter, the output of the first delay line connected to the first input of the second adder via the second line delays, and the output of the first lowpass filter is connected to the second input of the second adder and directly to the third input of the second adder via an amplitude limiter, with the output of the second adder connected to the input of the second lowpass filter. Sources of information taken into account in the examination I. Collection of technical information on communication issues, № 14. M., Gidrometeoizdat, 1977, p. 47, 54-59 (prototype). i P To the channel 12 cSgsu