Adjacent-channel interference (ACI) is

interference Interference is the act of interfering, invading, or poaching. Interference may also refer to: Communications * Interference (communication), anything which alters, modifies, or disrupts a message * Adjacent-channel interference, caused by extr ...

caused by extraneous

power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...

from a

signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...

in an

adjacent channel In broadcasting an adjacent channel is an AM, FM, or TV channel that is next to another channel. First-adjacent is immediately next to another channel, second-adjacent is two channels away, and so forth. Information on adjacent channels is ...

. ACI may be caused by inadequate filtering (such as incomplete filtering of unwanted

modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informatio ...

products in FM systems), improper

tuning Tuning can refer to: Common uses * Tuning, the process of tuning a tuned amplifier or other electronic component * Musical tuning, musical systems of tuning, and the act of tuning an instrument or voice ** Guitar tunings ** Piano tuning, adjusti ...

or poor frequency control (in the reference channel, the interfering channel or both). ACI is distinguished from

crosstalk In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired capacitive, induc ...

.Federal Standard 1037
Accessed: 2011-10-19. (Archived by WebCite at http://webcitation.org/62Z8qe0pC)
/ref>

Origin

The adjacent-channel interference which receiver A experiences from a transmitter B is the sum of the power that B emits into A's channel—known as the "unwanted emission", and represented by the ACLR (Adjacent Channel Leakage Ratio)—and the power that A picks up from B's channel, which is represented by the ACS (Adjacent Channel Selectivity). B emitting power into A's channel is called adjacent-channel leakage (unwanted emissions). It occurs for two reasons. First, because RF filters require a

roll-off Roll-off is the steepness of a Transfer function, transfer function with frequency, particularly in network analysis (electrical circuits), electrical network analysis, and most especially in connection with filter (signal processing), filter cir ...

, and do not eliminate a signal completely. Second, due to

intermodulation Intermodulation (IM) or intermodulation distortion (IMD) is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. The intermodulation between frequency compo ...

in B's amplifiers, which cause the transmitted spectrum to spread beyond what was intended. Therefore, B emits some power in the adjacent channel which is picked up by A. A receives some emissions from B's channel due to the roll off of A's selectivity filters.

Selectivity Selectivity may refer to: Psychology and behaviour * Choice, making a selection among options * Discrimination, the ability to recognize differences * Socioemotional selectivity theory, in social psychology Engineering * Selectivity (radio), a ...

filters Filter, filtering or filters may refer to: Science and technology Computing * Filter (higher-order function), in functional programming * Filter (software), a computer program to process a data stream * Filter (video), a software component tha ...

are designed to "select" a channel. Similarly, B's signal suffers intermodulation distortion passing through A's RF input amplifiers, leaking more power into adjacent frequencies.

Avoidance procedure

Broadcast regulators frequently manage the broadcast spectrum in order to minimize adjacent-channel interference. For example, in North America,

FM radio FM broadcasting is a method of radio broadcasting using frequency modulation (FM). Invented in 1933 by American engineer Edwin Armstrong, wide-band FM is used worldwide to provide high fidelity sound over broadcast radio. FM broadcasting is cap ...

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 first-adjacent 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."Code of Federal Regulations: Minimum distance separation between stations"

Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...

, October 1, 2019. 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.

References

{{Reflist Interference Electrical parameters

Origin

Avoidance procedure

See also

References