Posted on Feb 6, 2014

A simple radio receiver circuit is shown in Fig. 1. This receiver is designed for reception of signals of amateur radio stations operating in the SW band of 10, 15, 20, 40 and 80 meters. This direct-conversion receiver consists of a set of an input bandpass filters tuned to the middle frequency of the amateur bands, a broadband RF amplifier based

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on a transistor VT1, a diode mixer (VD1, VD2), a local oscillator (VT2) and a three-stage amplifier of audio frequency with high gain based on a transistors VT3-VT5. This amplifier is loaded with a headphones BF1. A switch SA1 is intended to switch between bands, it connects the filters to the input of the RF amplifier, and the mixer - to a corresponding resonant tank of the local oscillator. The local oscillator is tunable by a variable capacitor C27 and it generates an oscillations with a frequency twice lower than the frequency of received signals. A simple voltage regulator is based on the Zener diode VD3 and it is used to reduce a dependence of the local oscillator frequency of a supply voltage variation.

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