JPH0522170A - Squelch control circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction caused by jamming waves, etc., mixed into a reception band. CONSTITUTION:A modulation part 52 modulates the frequency of a local oscillation signal from a local oscillation part 7 according to a pilot signal generated by a pilot oscillation part 51 and transmits the signal to a transmitting frequency conversion part 6. A pilot detection part 53 detects the pilot signal, which is inserted to the transmitted signal on the side of a communicating opposite station, from the output signal of an AGC amplifier part 4 and controls a changeover switch 54 corresponding to whether the pilot signal is existent or not. When there is no pilot signal, the changeover switch 54 switches and outputs a squelch signal generated by a squelch oscillation part 55.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a squelch control circuit, and more particularly to a squelch control circuit applied to a microwave heterodyne repeater or the like.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing an example of a conventional squelch control circuit. In the microwave heterodyne repeater, a squelch control circuit 9 which detects a reception signal when it is in a disconnection state and sends out a squelch signal indicating the reception signal disconnection to a partner station is shown.

The signal received via the receiving antenna 1 is
The reception frequency conversion unit 2 converts the local oscillation signal from the local oscillation unit 3 into an intermediate frequency signal, and the AGC amplification unit 4 amplifies the intermediate frequency signal to a predetermined level, and then the transmission frequency conversion unit 6 transmits the local frequency signal from the local oscillation unit 7. The transmission signal is frequency-converted into a transmission signal, the power is amplified by the transmission amplification unit 8, and the signal is transmitted from the transmission antenna 10.

The squelch control circuit 9 detects the output signal level of the AGC amplification section 4 by the reception detection section 91 and detects the reception signal disconnection. When the disconnection of the received signal is detected, the changeover switch 92 is switched to send the squelch signal from the squelch oscillator 93.

[0005]

In the above-mentioned conventional squelch control circuit, squelch control is performed by detecting the presence or absence of a signal level. Therefore, for example, when an interference wave or the like enters the reception band, The received signal loss cannot be detected. For this reason, there is a problem in that the interference wave mixed in the reception band is amplified and transmitted as it is.

An object of the present invention is to provide a squelch control circuit which can prevent malfunction due to interference waves mixed in the reception band.

[0007]

The squelch control circuit of the present invention detects that a reception signal from one of the opposing relay stations is in a disconnection state and outputs a squelch signal indicating a reception signal disconnection to the other of the opposing squelch control circuits. In the squelch control circuit of the relay device for transmitting to the relay station, means for inserting a pilot signal into the transmission signal to be transmitted, means for detecting the pilot signal inserted at the opposing relay station side from the reception signal, and And a means for transmitting the squelch signal in response to the pilot signal detected by the detection means.

[0008]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. A signal received via a receiving antenna 1 is converted into an intermediate frequency signal by a receiving frequency converting section 2 and a local oscillating section 3 for AGC amplification. After being amplified to a predetermined level by the unit 4, it is frequency-converted into a transmission signal by the transmission frequency conversion unit 6 through the squelch control circuit 5, and further, the transmission amplification unit 8
Then, the power is amplified by and is transmitted from the transmitting antenna 10.

The squelch control circuit 5 includes a pilot oscillator 51 for generating a pilot signal to be inserted into a local oscillation signal for transmission and a modulator 52 for frequency-modulating the local oscillation signal from the local oscillator 7 with the pilot signal. And AGC
By switching the squelch signal generated by the squelch oscillating section 55 when there is no pilot signal and the pilot detecting section 53 which demodulates the pilot signal inserted in the other station from the output signal of the amplifying section 4 to detect the presence or absence of the pilot signal. And a changeover switch 54 for sending.

When an interference wave or the like is mixed in the reception band, the pilot signal from the partner station is disturbed by the interference wave or the like, so that it is impossible for the pilot detector 53 to detect the pilot signal. Become. Therefore, the changeover switch 54 switches and outputs the squelch signal, and thus it is possible to prevent the interference wave and the like mixed in the reception band from being amplified and transmitted as it is.

[0012]

As described above, according to the present invention, the local oscillation signal for transmission is modulated with the pilot signal to insert the pilot signal into the transmission signal, and the pilot signal inserted in the partner station is detected from the reception signal. However, by performing the squelch control according to the presence or absence of this pilot signal, there is no malfunction due to an interference wave mixed in the reception band. Therefore, it is possible to prevent the interference wave and the like mixed in the band from being amplified and transmitted as it is as in the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a conventional squelch control circuit.

[Explanation of symbols]

 5 Squelch control circuit 51 Pilot oscillator 52 Modulator 53 Pilot detector 54 Changeover switch 55 Squelch oscillator

Claims (1)

Claim: What is claimed is: 1. A relay which detects that a reception signal from one of the opposite relay stations is in a disconnection state and sends a squelch signal indicating a disconnection of the reception signal to the other opposite relay station. In the squelch control circuit of the device, means for inserting a pilot signal into the transmission signal to be transmitted, means for detecting the pilot signal inserted at the opposite relay station side from the reception signal, and this detection means And a means for transmitting the squelch signal in response to the pilot signal.