RF generator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Knots of amateur radio equipment. Generators, heterodynes
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I propose a GHF scheme with increased stability (Fig. 1). It has larger input and output impedances and less output capacitance than a standard inductive three-point.
The transistors are connected according to the "Common drain - common base" scheme, VT1 is used for decoupling. The output voltage of the generator is 0,1 ... 0,2 V. An additional circuit tuned to the fundamental frequency or harmonic can be included in the VT1 collector circuit (mandatory through a 50 ... 100 Ohm resistor). Possible options for switching on the main circuit are shown in Fig.2. Capacitor C2 may have a capacitance on the order of picofarads. The R2 slider is set to the lower position according to the scheme and moved until generation is obtained at the lowest frequency of the circuit. To obtain harmonics, the engine is set higher. If stability is not so important, but uniformity in amplitude is needed, full circuit inclusion is used. On the low bands, it is shunted with a resistor of several kOhm.
When turned on according to the scheme of Fig. 2a, it is necessary to achieve generation at the lower frequency of the circuit by the number of turns before the tap in coil L1, because excitation occurs at the parasitic frequency of the lower part of the coil.
In the diagram of Fig. 2d, the capacitance C2 for HF bands is several hundred picofarads. Quartz ZQ is also excited on harmonics.
The generator operates at a supply voltage of 7 ... 24 V. Its disadvantage is the initial frequency overrun, since the voltage on the circuit can be tens of volts (in the circuit of Fig. 2E it is equal to Ukb VT3). C6 must have a minimum lead length. The generator operates stably at frequencies from 10 kHz to 200 MHz and higher (determined by the parasitic capacitance SkeVT3).
Author: V. Klimovich, town of B. Berestovitsa; Publication: N. Bolshakov, rf.atnn.ru
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