Radio and Electronics Cookbook

63

The absorption wavemeter

Introduction

The purpose of the absorption wavemeter is to check that a transmitter is radiating within the correct waveband, and to detect any spurious harmonic emissions. A harmonic frequency is an integral multiple of the carrier frequency – e.g. if the carrier is at a frequency f, the harmonics are at frequencies 2f, 3f, 4f … and so on.

It can also be employed as a relative field-strength indicator, being used in experimentation with aerials. What it cannot do is to measure the transmitted frequency accurately; all it can do is to place the signal within a particular band, say the 7 MHz or the 18 MHz band (or their harmonics).

How it works

You may recognise the circuit of Figure 1 as a crystal set with a meter ...