Automated search for correspondents. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Automated search for correspondents. 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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During the period of low activity of amateur stations in the range of 144-146 MHz, it takes considerable time to search for correspondents. To facilitate this task, various automated search devices are used. A diagram of one of them is shown in the figure. It is used in a 144/28 MHz converter whose local oscillator frequency is stabilized by quartz (38,667 MHz). The frequency of 38,667 MHz is then tripled. In an automated search, instead of a quartz oscillator, the described device is switched on, which provides automatic change in the frequency of the local oscillator master from 38,3 to 39 MHz.

Frequency tuning occurs with the help of the D1 varicap, which is included in the circuit of the master oscillator assembled on the T3 transistor. The control voltage is obtained by integrating the R5C4C5 chain of rectangular pulses coming from the multivibrator (transistors T1 and T2). The duration of one cycle of automatic tuning is about 20 s.

Automated search for correspondents

To simplify switching, both master generators (the circuit of the main generator is not shown in the figure) are assembled on one board. Their outputs are combined. Thus, to switch the generators, that is, to switch from manual to automated search, you only need to switch the power to the generators.

The device uses mainly ceramic capacitors (C3, C5, C8, C10-C13}. Capacitor C4 must have a small leakage current. Coil L1 contains 11 turns (removal from the third turn) of copper wire with a diameter of 1 mm. Coil diameter 6 mm, length its 20 mm.

The output voltage of the master oscillator is at least 1,5 V.

In the automated search device, transistors KT315B can be used. any varicap from the D901 series. The inductance of the inductor Dr1 should be approximately 100-200 μH.

Literature

"Radio REF" (France), 1974. No. 10

Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Civil radio communications.

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