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10 / 11 m reflex superhet using crystal control

This receiver is a complete superheterodyne with RF preamp, mixer with crystal-controlled oscillator, an AM demodulator, a two-stage IF amplifier with AGC and also a two-stage audio amplifier with push-pull output stage. Due to the multiple use of stages, the circuit works with a total of only six transistors. The RF preamplifier works with a 2SC1674 in grounded base circuit. This stage has no special features and is regulated together with the first IF stage via the DC component on the AM diode demodulator. The crystal-controlled oscillator simultaneously works as a mixer. So it is thus a self-oscillating mixer, which has a very good frequency stability as a result of crystal control. The second IF stage at the same time serves as a reflex stage the audio preamplification. It feeds via the driver transformer directly to the following push-pull output stage.

It was a special challenge for me to make such a superhet to work. Unlike what I feared, that was not so difficult. The decisive factor is the RF-compliant design with sophisticated cable routing. Measured at the lower expense, the receiver had an excellent input sensitivity and a completely sufficient overall gain. Following to the first IF resonant circuit, I experimentally inserted a ceramic filter, which significantly improved the selectivity. Despite the much smaller effort, the overall features of this circuit were hardly worse than the receiving parts of old CB base stations with single conversion superhet.

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