Low-power broadcasting
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Low-power broadcasting is the concept of broadcasting at very low power and low cost, to a small community area. These stations tend to serve small towns, if not completely rural areas in the United States, largely because they cannot fit into large cities already crowded by full-power stations. The terms "low-power broadcasting" and "micropower broadcasting" (more commonly "microbroadcasting") are sometimes used interchangably. However, the former term is more often used to describe stations who have applied for and received official licences. The latter are more often used to describe stations that have not applied for such licences and broadcast illegally.
LPFM, LPAM, and LPTV are in various levels of use across the world, varying widely based on the laws and their enforcement.
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United States
Criticisms of LPFM
Many of the proponents of the new LPFM classes have been critical of the actual service. Their complaints include:
- The majority of the licensed have been issued to religious broadcasters who tend to have little locally-produced programming. Religious broadcasters counter that few secular groups are equipped to fund the continuing operations of an LPFM station.
- Of the religious broadcasters, a large number have been issued to local branches of Calvary Chapel.
- In some states, the local Department of Transportation operates large networks of LPFM stations that act as Highway Advisory Radio stations - a service traditionally operated at the fringes of the AM band - restricting the number of available channels.
- In most large metropolitan areas there are no available frequencies for LPFM stations at all.
FM radio
In the U.S., the FCC finally re-legalized LPFM licenses, after the NAB, CPB, and NPR convinced them to stop issuing the FM class D license in 1978, which continues to force many stations off the air.
LPFM classes in the United States
- Class L1 (LP100) is from 50 to 100 watts ERP.
- Class L2 (L10) is at least 1 and up to 10 watts ERP.
- Class D is 10 watts TPO or less, regardless of ERP, and are no longer issued for LPFM services (since 1978).
Officially, class D is still assigned to broadcast translators, though the rules are actually much looser (up to 250 watts ERP) than for true LPFM stations, though they may not broadcast their own programming. This is due to the influence of NPR and religious broadcasting companies, which often rely on translators. Since true class D stations can bump translators, they therefore have less competition in getting or keeping their own translators on the air with new class D stations kept off the air.
New classes L1 and L2 are still considered class D for international purposes, but are considered to be equal in status to translators, and subordinate to full class D stations still operating.
Part 15 rules are quite strict for FM, making it nearly impossible to operate a legally-unlicensed station that can be heard more than a few meters away. The rule is a signal strength of 250µV/m² at 3 meters from the antenna, set forth in 47 CFR §15.239.
AM radio
LPAM is generally not licensed in the U.S., but is allowed on the campus of any school, so long as the normal Part 15 rules are adhered to when measured at the edge of the campus. Most college radio stations started out this way. Stations may have freestanding radio antennas, or may use carrier current methods to ride on power lines. These signals cannot pass through transformers, however, and are prone to the electromagnetic interference of the alternating current.
The exception is Travelers' Information Stations (TIS), sometimes also called highway advisory radio (HAR). These are licensed LPAM stations set up by local transport departments to provide bulletins to motorists and other travelers regarding traffic and other delays. These are often near highways and airports, and occasionally other tourism attractions such as national parks. Only governments may have licenses for TIS/HAR stations, and music is disallowed.
Television
LPTV is common in the U.S., Canada and most of the Americas where stations are free to either originate their own programming, or to relay a main TV station as a broadcast translator. Some LPTV stations which broadcast their own programming were allowed a slight upgrade to a new "class A" status.
Unlike FM and AM, unlicensed use of TV bands is prohibited for broadcasting. The amateur television channels do allow for some very limited non-entertainment broadcasting however, with some repeaters airing NASA TV during Space Shuttle missions when they are not in local use.
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United Kingdom
Temporary low-power stations are allowed at times via a Restricted Service Licence.
Since 2001 longterm LPFM licences have been available in remote areas of the country. These are currently used for many establishments including Army Bases, Universities and Hospitals with fixed boundaries.
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