Radio and Electronics Cookbook

27

The Colt 80 m receiver – Part 4

Introduction

In Parts 1 to 3 of this series, the design of an 80 metre direct-conversion receiver has been described. In this final part, we are going to change the circuit to operate as a superheterodyne receiver, or superhet. Most radio receivers are superhets, and they change the incoming signal to another frequency, known as the intermediate frequency, or IF, before producing an audio signal. The use of a superhet in a good receiver is mandated by the requirements for good sensitivity and selectivity.

Sensitivity and selectivity

Figure 1 shows the block diagram of the receiver. If you look closely, you will see that it is two similar circuits, one after the other. The incoming signal is filtered and ...