JPH0445676A - Squelch method in television relay equipment - Google Patents

Abstract

PURPOSE:To enable a secure operation without being affected by the output level of a demodulation circuit by controlling squelch according to the presence/ absence of a noise component. CONSTITUTION:One end of a band pass filter 5 having a central frequency 5MHz and narrow band width is connected between a video modulator 3 and a low-pass filter 4, and a squelch control signal is outputted while detecting the 5MHz component by a detector 6. The squelch control signal can control an IF output by controlling a power supply switch 7 of an amplifier 8 for IF repetition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a squelch method for a receiving device of a television relay device.

[Summary of the invention]

The squelch method in conventional television relay receiving equipment observes the peak-to-peak value of the demodulated video output level, and utilizes the fact that when the receiving input electric field decreases and becomes noise, it is usually 2 to 3 times the demodulated video output level. and determines the height of the received input electric field.

It was used as a squelch control signal, but the video level was too high,
Malfunctions could occur due to bounces, etc.

The present invention extracts a required frequency between the video and audio bands of the demodulated video output and uses it as a squelch control signal to avoid being affected by an excessive video level or bounce.

[Conventional technology]

Conventionally, in television relay receivers, when AGC is applied, the normal demodulated video output level is IVp-p, but when the input electric field decreases and becomes noise specific power,
The noise level becomes 2 to 3 Vp-p or higher.

When the IF output of this receiving device is used for relaying, the input electric field strength decreases and the noise level becomes large, causing problems in line operation. A squelch circuit is provided to cut off the output.

Conventionally, the peak-to-peak value of the demodulation level is detected, the normal video output level is distinguished from the noise level, and when this value exceeds a predetermined value, a squelch circuit is activated as a squelch control signal to use the relay signal. The output of the IF amplification number is cut off.

[Problem to be solved by the invention]

In the case of the above-mentioned conventional method, the peak-to-peak value of the demodulation level changes due to excessive video level due to overmodulation or bounce, which may be mistaken for noise output.

In order to solve this drawback, the present invention is based on the presence or absence of noise components rather than the peak-to-peak value of the demodulation level.
It controls squelch.

It is an object of the present invention to provide a squelch method that operates reliably without being affected by the output level of a demodulation circuit.

[Means to solve the problem]

In order to achieve the above object, the present invention connects two bandpass filters, for example, with a center frequency of 5 MHz and a narrow band, between the demodulation circuit and the video low-pass filter, and branches the demodulated output. Since the video signal band is 4.5 MHz and the lowest audio subcarrier frequency is 6.0 MHz, nothing is output from the bandpass filter except for low input electric fields, and the demodulated signal at low input electric fields The noise is output, and since the noise is broadband, by a bandpass filter.

A 5 MHz component is extracted.

A squelch control signal is output depending on the presence or absence of this bandpass filter output.

[Effect]

As a result, even if the demodulated output level fluctuates, the squelch control signal is not affected, so stable squelch control can be performed.

〔Example〕

The following two embodiments of the present invention will be explained with reference to Fig. 1. Fig. 0 shows the system from the intermediate frequency (IF) signal in the receiving device to the video output. So, for IF relay.

The 0-distributed IF multiplied signal for video demodulation is demodulated by the video demodulator 3 and passed through the low-pass filter 4 to become a video output. One end of a band-pass filter 5 with a center frequency of 5 MHz and a narrow bandwidth is connected between the video demodulator 3 and the low-pass filter 4, a 5-MHz component is detected by a detector 6, and a squelch control signal is output. Squelch control signal.

By controlling the power switch 7 of the IF relay amplifier 8, the IF output can be controlled.

For example, at a receiving frequency of 7G)lz, the input electric field strength is -7
When the input electric field strength is 5 to -80 dB or less, the noise increases rapidly, but the detector 6 is designed to be able to detect the noise at the above-mentioned input electric field strength.

〔Effect of the invention〕

According to the present invention, the relay IF specific pressure can be controlled without fluctuations in the demodulated output level or influence by balance.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. 1: IF amplifier, 2: distributor, 3: video demodulation amount. 4: Video low-pass filter = 5: 5MHz narrow bandwidth bandpass filter. :Detector. 7: Switch. 8: IF amplifier.

Claims (1)

[Claims] 1. In the receiving device of the television relay device, wideband random noise of the demodulated output is extracted by a narrowband bandpass filter in the middle band between the video band and the audio band, and when this noise is detected, the height of the receiving input electric field is detected. A squelch method in a television relay device, which is characterized in that it uses a signal for determining the IF relay output and turns on and off the power of the final stage amplifier of the IF relay output.