Wednesday, December 7, 2022

MOSFET based Preamplifier for FM Radio DXing

This is a circuit for a MOSFET based FM preamplifier that provides a gain of about 18 dB. -- N.S. HARISANKAR,VU3NSH

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You can use a folded dipole or any other antenna. However, an excellent performance is obtained with a cubical quad antenna (refer Fig. 2) and Sangean ATS-803 world-band receiver.

Fig. 2: Different antennae used for FM DXing
Fig. 2: Different antennae used for FM DXing

Advantages of this MOSFET based preamplifier

In an amplifier, FET is immune to strong signal overloading. It produces less cross-modulation than a conventional transistor having negative temperature coefficient, doesn’t succumb to thermal runaway at high frequencies, and decreases noise. In VHF and UHF, the MOSFET produces less noise and is comparable with JFETs. DG FETs reduce the feedback capacitance as well as the noise power coupled to the gate from the channel, giving stable unneutralised power gain for wide-band applications.This circuit can be used for other frequency bands by changing the input and the output LC networks. The table here gives details of the network components for DXing of stations at various frequency bands.


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