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LPFM Frequently Asked Questions: Technical

Q. Can an LPFM station broadcast with a used transmitter that was donated to us by another radio station?
A. The transmitter model used in the LPFM service must be certified for use in the service.  Not all transmitters are certified, especially used "hand me down" transmitters.  The other broadcast services have a different requirement than LPFM does.  The transmitter MUST have a label that has the words "FCC ID", followed by the certification code.  A list of certified transmitters known to REC can be found at this page.  Transmitters must be certified for Part 73.

Q. I see inexpensive transmitters on Amazon and eBay.  Can I use one of those?
A. Most likely not. Honestly, most of those transmitters are "junk" and in many cases, do not even have the Supplier's Declaration of Conformity used in the other broadcast services.  Some will claim they are "FCC type accepted", "FCC type verified", etc.  Some will even give a certification ID number.  In some cases, that may be for a different part of the rules (such as Part 15) and we have found in some cases, ID numbers advertised were found to be with totally different units.  We suggest avoiding the e-commerce sites and dealing directly with either the manufacturer or a reputable dealer.  

Q. Why does LPFM have this specific requirement for certified transmitters?
A. In the late 1990s, after the passage of the Telecommunications Act, which mandated the lifting of national ownership limits on radio stations, there was a surge of "pirate" radio stations (those operating without broadcast licenses).  In the FCC rulemaking proceedings that preceded the creation of the LPFM service, the FCC received a large number of comments defending the pirate radio movement and called for the ability for new licensed LPFM stations to build their own transmitters from kits, which in reality are not controlled and can be unstable.  Unstable transmitters are a hazard to public safety as they can transmit on other frequencies at the same time as the intended frequency.  This is also known as spurious emissions.  Sometimes, these kit built transmitters would result in pirate stations being heard on frequencies used by aircraft.  The FCC decided in 2000 that the certification requirement was the only way to assure that "clean" transmitters were used in the service.  Also, modern certified transmitters have additional circuitry that prevents out of compliance conditions and require less TLC, even less than older broadcast transmitters, that required more adjustments and monitoring (meter reading) than the modern transmitters.  

Q. How far will the station be heard?
A. On flat terrain with the antenna at the exact height to make 30 meters height above average terrain, the effective range of a LPFM station is approximately 3 to 4 miles.  There are various factors that can impact how far the station can be heard.  This includes the surrounding terrain, the antenna height, the type of antenna used and the location of nearby stations on the same frequency or one channel away.  REC can advise of stations that may potentially interfere with the station and give some insight on what the coverage may be. 

Q. I heard that if I get a "high gain" antenna, the station will be heard farther.  Is that true?
A. LPFM stations are licensed using "effective radiated power" (or ERP).  Using the ERP method, the power assigned based on the power at the antenna.  The ERP is calculated taking into consideration how much power is coming from the transmitter, the amount of signal that is lost in the feedline (the wire that runs between the transmitter and the antenna) as well as the characteristics of the antenna, which can either result in gain or loss.  If a station is licensed for 100 watts ERP.  Then the 100 watts is based on all these factors.  If an antenna exhibits gain, then its gain will be partially or fully offset by the loss in the feedline (longer runs of feedline have more loss).  A calculation needs to be done to determine what power needs to be run at the transmitter in order to achieve the authorized ERP.  Going with a high gain antenna only means that you can run less power from the transmitter. 

Q. When I tune across the radio, I hear quiet spots on the dial where there are no stations.  When I check the LPFM Search Tool, it states that there are no channels available and when I check the list, it shows a station that I cannot hear.  Can we still apply for that channel?
A. No. The FCC has specific distance separation rules that apply to LPFM stations. The FCC follows these rules when authorizing LPFM stations. If anything, the FCC is under a congressional mandate to use these distances in respect to full-power FM stations.  Just because a channel may be quiet where you are at does not mean that it is quiet everywhere.  We are unable to accommodate any requests for waivers of the distance separation rules.  Distance separation rules can only be waived for "second-adjacent" (+/- 2 channels, +/- 0.4 MHz) and only in cases where a technical showing demonstrates a lack of interference to nearby occupied structures. 

Q. The "vacant channels" tool in shows potential channels, but I do not see similar channels listed here. Why?

A. The vacant channel search on Radio Locator is intended for very short range license free "Part 15" devices, such as those little transmitters you can install in your car's lighter plug in order to listen to your cell phone on the car radio.  For the LPFM service, allocations are based on specific distances determined by the FCC in §73.807 of the FCC Rules.   All LPFM stations must meet those minimum distance separations.  Like as mentioned in the previous question, just because there is a "quiet spot" on the dial does not mean that channel is available for LPFM use.