SU1385237A1 - Method of generating single-band television signal - Google Patents

Abstract

The invention relates to radio engineering and TV technology. The purpose of the invention is to reduce the unpressed balance of the suppressed sideband. Spb -b is based on multiplying the input video signal with a carrier frequency signal and suppressing one sideband (BPF). To reduce the unpressed balance of the suppressed BPF, the input video signal is sampled at even and odd reading points (OT). Subtract from the even OT component and the OT component is filtered and the low-frequency components are filtered in the frequency band to Fa, FJ g where F is the sampling frequency, F p is the upper limit frequency of the input video signal. 2 Il. o (l

Description

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The invention relates to radio engineering and television technology and can be used to form a single-band signal mainly in the transmitting television equipment, as well as in communication technology and magnetic recording.

The purpose of the invention is to reduce the unpressed balance of the suppressed sideband.

Fig. 1 shows explanatory time diagrams; in fig. 2 is a structural electrical circuit of the device implementing the proposed method of forming a single-sided television signal-a.

The proposed method for generating a single-band television signal is as follows. When forming a single-band signal from an amplitude-modulated signal, the suppression of one sideband presents considerable technical difficulties, since the lower limit frequency of the spectrum of the modulated television input video signal differs little from the carrier frequency. The undressed balance of the suppressed sideband is relatively large. Therefore, the spectrum of the original informational television video signal (Fig. 1a) 5, whose maximum power is concentrated in the lower frequency range, is converted as follows: the low-frequency part of the spectrum goes to the higher frequencies, and the high-frequency part occupies the low frequencies (Fig. 16). Then the generated signal is multiplied with the carrier signal, resulting in two sidebands (Fig. 1c), one of which (lower) is suppressed by filtering. The parts of the spectrum of the sidebands of the television signal, in which the minimum part of the energy is concentrated, are now located near the carrier frequency f ,, therefore, by filtering with a bandwidth, one (upper) sideband of the frequencies is extracted with almost no remainder of the second (lower) sideband (FIG. . 1d).

A device that implements the proposed method of forming a single-band television signal, contains (Fig. 2) the source 1 of the input video signal, the first low-pass filter

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(LPF) 2, clock pulse generator (GTI) 3, first sampler 4, delay line 5, second sampler 6, emitter 7, second low-pass filter (LPF) 8, balanced modulator 9, carrier frequency generator 10, band-pass filter 11 .

The device works as follows

The input video signal from source 1 passes through the first low-pass filter 2, the frequency band of which is chosen equal to the width of the spectrum of the input video signal / SF. From the LPF 2 signal, the signal is fed to the inputs of samplers 4 and 6. The sampler 4 samples the video signal at even reading points at intervals of 2at, the sampler 6 discretes the video signal at odd reading points at intervals of 2лt, and at 1 / 2Fj p is the Kotelnikov interval, where Fgrp cutoff frequency of the input video signal. The second inputs of discretizers 4 and 6 from the GTI 3 receive short pulses, and they go directly to the input of discretizer 4, and to the input of discretizer 6 through a delay line 5. At the same time, short pulses follow with a period equal to two Kotelnikov intervals 2at, and the delay in delay line 5 is one interval at. From the outputs of the bottom and the kretizers 4 and 6, the video signal samples are passed to the reader 7, where one is subtracted from the other, and from it is fed to the input of the low-pass filter 8 from the PSR band, which filters the low-frequency components in the frequency band to Fg. V. gr D Fn - sampling rate. Then the output signal of the low-pass filter 8 arrives at the balanced modulator 9, to another input of which a carrier frequency signal is received from the oscillator 10. From the output of the balanced modulator 9 a two-band signal with suppressed carrier frequency is fed to the band-pass filter 11, which passes only the upper sideband. At the output of the band-pass filter 11, a single-band signal is received with a reduced balance of suppressed sideband. When using the generated signal when transmitting a television signal at the receiving side, after heterodyning demodulation and filtering by a low-pass filter,

receive a signal similar to the original input video signal (Fig. 1e).

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The formula of the invention is a method of forming a single-band television signal based on multiplying the input video signal with a carrier signal and suppressing one sideband, characterized in that, in order to reduce the unsuppressed

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the remainder of the suppressed sideband, the input video signal is pre-sampled by even and odd sample points, subtracted from the component with even sampling points by many odd sample points, and low-frequency components are filtered out in the band

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frequencies to FJ Fgrp, where

sampling, F - upper bound frequency of the input video signal.

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Claims (1)

Claim A method of generating a single-band 5 television signal based on multiplying the input video signal with a carrier frequency signal and suppressing one side frequency band, characterized in that, in order to reduce the unsuppressed balance of the suppressed side frequency band, the input video signal is pre-sampled by even and odd reference points, subtracted component of the even reference point component with odd reference point and filtered low-frequency components in the frequency band up _to F = F _(), Where F - sampling rate, F _{B c} - upper limiting frequency of the input video signal. Fi $ .1 Fig.?.