Automated search of correspondents
In the period of low activity of the Amateur stations in the band 144-146 MHz in search of correspondent takes a long time. To facilitate this, various devices are used for automated searching. Diagram one shows in the picture. It is used in the Converter 144/28 MHz, the frequency of the local oscillator which is stabilized by quartz (38,667 MHz). Frequency 38,667 MHz then tripled. In the automated search instead of the crystal oscillator is enabled the described device, providing automatic change of the frequency of the master oscillator of the local oscillator from 38,3 to 39 MHz.
Frequency tuning is done via varicap D1 included in the master oscillator circuit, assembled on the transistor T3. Control voltage is obtained by integrating the chain R5C4C5 rectangular pulses received from the multivibrator (transistors T1 and T2). The duration of one cycle of the automatic adjustment is about 20 C.
To simplify the switching of both the master oscillator (circuit of the main generator in the figure not shown) were collected and a single Board. Their outputs are combined. Thus, to switch the generators, that is, to switch from manual search, automated, just need to switch the power generators.
In the device used mainly ceramic capacitors (C3, C5, C8, C10-C13}. Capacitor C4 should have low leakage current. Coil L1 contains 11 turns (removal from the third round) copper wire of diameter 1 mm. coil Diameter 6 mm, length 20 mm.
The output voltage of the master oscillator is not less than 1.5 V.
In the device of the automated search, you can use transistors KT315B. any varicap from D. The inductance of the inductor DR1 should be about 100 - 200 mcg.
Publication: N. Bolshakov, rf.atnn.ru