no pattern is seen when the transmflter is not modulated. when the transmitter is modulated, permitting one sideband to be radiated, the effect is of moving whfle bands as for AM.

b. Diathermy - hospflal deep heat treatment. The transmitter is powered by raw AC and thus produces an output modulated at 50 Hz. The effect is a band of interference across the screen which. since the field is not locked to the mains frequency. moves up or down.

e. RF Paging Systems There are various forms of paging but those operated by tone modulation of the carrier produce an effect similar to speech modulated AM. with the horizontal white bands fixed or slowly moving.

Inteference effects on radio

Broad band interference appears as a continuous buzz where the interfering device is a commutator motor, or a short buzz or click where the cause is a thermostat or other type of switch.

Narrow band interference may appear as a whistle. distortion, or as unwanted speech.

Check charts

The Check Charts on the following pages, with their related notes, give a step-by-step problem- solving sequence covering the aerial and feeder; the receiver and direct pick-up which will provide for most situations. Although the check charts are designed primarily around problems of television receivers they can also be applied to radio receivers.

It is strongly recommended that problem solving commences at Check Chart 1 progressing through Check Charts 2 and 3 as necessary. However. there will be occasions when your own experience combined with the particular type of problem will allow you to dispense with the full sequence.