This is a design for amplify the input from a telescopic whip antenna. This circuit is based on MOSFET. Here’s the circuit diagram.
Operation of this circuit is begin when RV1 is the gain control allowing weak signals to be amplified or strong signals to be attenuated. The control voltage is applied to gate 2 of TR1, a dual-gate MOSFET, the signal voltage applied via gate 1; the input signal being double tuned via the 330uH coil and the two KV1235 varicap diodes at the MOSFET's input and by the same components at the BF981 MOSFET's drain terminal. Both tuned circuits provide high selectivity across the entire tuning range. To aid stability the MOSFET stage is fed from a 6.2V zener stabilized supply.
The preamplifier is designed to cover the medium waveband from about 550Khz to 1650Khz. The tuning voltage is supplied via RV2, a 10k potentiometer connected to the 12 Volt power supply.
Operation of this circuit is begin when RV1 is the gain control allowing weak signals to be amplified or strong signals to be attenuated. The control voltage is applied to gate 2 of TR1, a dual-gate MOSFET, the signal voltage applied via gate 1; the input signal being double tuned via the 330uH coil and the two KV1235 varicap diodes at the MOSFET's input and by the same components at the BF981 MOSFET's drain terminal. Both tuned circuits provide high selectivity across the entire tuning range. To aid stability the MOSFET stage is fed from a 6.2V zener stabilized supply.
The preamplifier is designed to cover the medium waveband from about 550Khz to 1650Khz. The tuning voltage is supplied via RV2, a 10k potentiometer connected to the 12 Volt power supply.
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