# Transmitter interference

Frequency drift and chirp are due to changes in oscillator frequency. Drift is a gradual change which can be caused by a number of factors. Chirp is a rapid change due to the loading effect of keying.

Modulation produces sidebands, and sidebands must be limited in their width to ensure occupancy by as many people as possible. For a given audio frequency input, the bandwidth of a double sideband, full carrier transmission will be twice as large as that of an SSB transmission unless filtering is used. Distortion produced by over-driving a linear power amplifier can produce splatter. Splatter can also be caused by over-modulation of an AM transmitter, or by too wide a range of modulating audio frequencies.

Low-pass and high-pass filters permit the passage of low frequencies and high frequencies respectively. A trap filter suppresses one particular frequency.

A good short low-resistance external RF earth is an essential requirement of an HF transmitting station. The use of a water supply pipe should be avoided.

Interference can take many forms. Some of the causes of interference have been dealt with in previous sections, since they are associated with transmitters, their construction and operation. Parasitic oscillations are caused by the inductance and capacitance of the circuit wiring, and can cause interference on a wide range of frequencies.

The ideal HF transmitting station will have its transmitter connected to the antenna via a V.S.W.R. meter, low-pass filter and antenna tuning unit.

The following problems are additional to those previously given.

Questions

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