The Radioman's Manual of RF Devices, Principles and Practices
Dealing with the RF aspects of radio communication, this is an indispensable book for anyone involved in land mobile radio, ham radio, marine radio or aviation radio.
TABLE OF CONTENTS The Radioman's Manual of RF Devices, Principles and Practices
Chapter 6: Intermodulation, Transmitter Noise & Receiver Desense
In the real world of RF communication, problems such as intermodulation interference, transmitter noise and receiver desensitization (desense) must be addressed. This chapter provides an understanding of these different types of interference and what can be done to mitigate or greatly reduce the level of the interference.
6.1 Intermodulation Interference
If two RF signals (A and B) are applied to the input of an RF amplifier, only these two signals appear (at a higher level) at the output if the amplifier is perfectly linear. Linearity of the amplifier depends upon the design and type of amplifier. However, even an amplifier designed to operate in the linear mode can become nonlinear if excessive signal levels are applied at the input. In the practical world, no amplifier is perfectly linear, i.e., the output signal is never an exact replica of the input signal. This nonlinearity results in the presence of distortion signals or products at the amplifier output.
The frequency of these distortion products include harmonic distortion such as 2A, 3A and so on as well as intermodulation distortion, such as A ?B, B ?A, 2A ?B, 2B ?A, 3A-2B, 3B-2A, and so on. Simple harmonic distortion products are called single-signal distortion products. The intermodulation products listed above were derived from two signals and are called two-signal distortion products. Three-signal distortion products are also possible. If a third tone, C, were present at the input, a three-signal mix could produce a distortion product at frequencies of A+B+C, A+B ?
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