World Library  
Flag as Inappropriate
Email this Article

Adjacent-channel interference

Article Id: WHEBN0000040699
Reproduction Date:

Title: Adjacent-channel interference  
Author: World Heritage Encyclopedia
Language: English
Subject: Digital television in the United States, Digital television transition in the United States, Index of electronics articles, Multi-band device, Amateur Station Operator's Certificate
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Adjacent-channel interference

Adjacent-channel interference (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 FM systems), improper tuning or poor frequency control (in the reference channel, the interfering channel or both).

ACI is distinguished from crosstalk.[1]

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

References

  1. ^ Federal Standard 1037C Accessed: 2011-10-19. (Archived by WebCite at http://webcitation.org/62Z8qe0pC)
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from Hawaii eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.