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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Standby mode in the CB radio station. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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All users of the civilian range know how much inconvenience delivers long-range travel. Especially when it comes to business communications. The use of radio stations in such conditions becomes simply not possible, as it forces your correspondent to turn the squelch up to the stop or even turn off the volume. Yes, and in a clean air, not everyone wants to listen to the conversations of radio amateurs on your duty frequency. In order to get away from these troubles, paging systems using the DTMF code are used. But this is not available to everyone - both due to the cost and due to the lack of an element base.

I propose a simple device scheme available for repetition by almost every radio amateur, built on cheap affordable elements. This design has been used for several years in many radio stations and has worked flawlessly.

The device works on the principle of selective calling and performs the following functions:

1. Securely blocks the station on reception in the absence of a call.
2. Opens the station when there is a call signal, regardless of the position of the SHP knob.
3. Automatically switches the station to normal operating mode at the start of communication.
4. Automatically transfers the station to standby mode at the end of communication, after 20-30 seconds, which does not require any additional actions from the operator.
5. There is a switch to the normal mode, but the function of turning off the SHB with a call signal is preserved, which allows you not to miss it if the connection is not sure.

The device (Fig. 1) is made on a single K561LN2 chip, consisting of six logic elements.

Standby mode in the CB radio station. Scheme
Fig.1 (click to enlarge)

The operation of the circuit is very simple. The low-frequency signal taken from the detector (simpler than the upper end of the volume control) is fed to the DD1.1 limiter amplifier, then to the DD1.2 resonant amplifier, the DD1.3 threshold device (which generates pulses when a 1400 Hz tone signal appears), inverter DD1.4, through the integrator of positive pulses to the inverter DD1.6, which blocks the station's squelch. To do this, output 3 of the device is connected to the base of the transistor switch in the station, which controls the squelch. From the DD1.5 inverter, a positive potential for prohibiting the opening of the SR in the initial position is also supplied there. The barring signal is removed when the call goes through and after pressing the transfer. To do this, pin 2 is connected to the station at the point of appearance + when transmitting.

To make a call, a conventional multivibrator at 1400 Hz, controlled by a button, is built into the station, the output of which is connected through a 100 KΩ resistor to the signal circuit of the microphone path.

Author: Alexander Shatun, Dergachi, Kharkiv region; Publication: N. Bolshakov, rf.atnn.ru

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