Adjacent-channel interference

Adjacent-channel interference or ACI is interference caused by extraneous power from a signal in an adjacent channel. ACI may be caused by inadequate filtering, such as incomplete filtering of unwanted modulation products in frequency modulation (FM) systems, improper tuning, or poor frequency control, in either the reference channel or the interfering channel, or both.

ACI is distinguished from crosstalk.

Broadcast regulators frequently manage the broadcast spectrum in order to minimize adjacent-channel interference. For example, in North America FM radio stations in a single region cannot be licensed on adjacent frequencies — that is, if a station is licensed on 99.5 MHz in a city, the frequencies of 99.3 MHz and 99.7 MHz cannot be used anywhere within a certain distance of that station's transmitter, and the second-adjacent frequencies of 99.1 MHz and 99.9 MHz are restricted to specialized usages such as low-power stations. Similar restrictions formerly applied to third-adjacent frequencies as well — i.e. 98.9 MHz and 100.1 MHz in the example above — but these are no longer observed.

See also

Co-channel interference

References

• Federal Standard 1037C
• MIL-STD-188

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