Superhet Receiver on a 40-Meter Popcorn Version

Overview

This Superhet Receiver does not require AGC or RF control since it has satisfactory large signal handling capability as it operates with 4MHz intermediate frequency.

Explanation

Only 6 bipolar transistors are used by this receiver along with an op-amp for sufficient volume into headphones. To terminate the diode ring mixers, one of two RF and AF diplexers are used. The RF amp is a 50Ohm feedback amp which has input impedance that properly terminates the band pass filter. To help provide a 50Ohm input impedance for the mixer, the receiver uses the -6dB attenuator pad following the amp. It also provides aid in preserving the signal to noise ratio of the receiver by reducing the stage gain. Reducing the PI attenuation to -3dB may affect the receiver dynamic range but it could add a little more sensitivity.

The ring mixer uses a 50Ohm diode and is followed by a RF diplexer. To protect the crystal filter from a catastrophically large signal to be present in the receiver’s front end, a 13dB limiter is formed by the four diodes. Unwanted ripples are prevented in the pass band by matching IF filter crystal frequency.