VFO with electronic tuning. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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VFO with electronic tuning. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes

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I want to offer a VFO circuit that has been working for a long time and has proven itself on the positive side.

The oscillator circuit is part of the mixer type VFO for a single conversion transceiver.

(click to enlarge)

The range of overlapped frequencies is 4812...5312 kHz. The initial overrun of the frequency for 2 minutes after switching on is 260 Hz. In the future, frequency stability is 15 ... 20 Hz.

The generator itself is made on transistors VT2 VT3 according to the analog circuit of a lambda diode. This scheme has increased temperature stability and low non-linear distortion. The current consumed by the generator is 220 ... 230 μA. On the elements VT1, DA1 a voltage regulator is made to power the generator. VT4 is a source follower for decoupling the generator from the influence of subsequent stages. Setting the generator is reduced to setting the range of overlapping frequencies using C5 and C6 and setting the operating point of the generator. To do this, using R3, the voltage at point A is set equal to 2,65 ... 2,75 V.

Author: I. Ptashnik (RB5UM), Ukraine, Kiev region, Bucha village; Publication: N. Bolshakov, rf.atnn.ru

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