Occasionally, REC receives questions in regards to low power broadcasting and whether a license is required to use a particular piece of equipment. In most cases, it turns out that the device is being inquired about is illegal for usage in the United States, Canada and the European Union. Much of this equipment is imported from China and is sold through Ebay and similar sites. Recently, we have spotted illegal equipment being sold on Amazon.com.
What is legal in the USA?
In the United States, there are services (such as LPFM) that are licensed and the ability to use extremely low power transmitters by rule.
If you are the permittee or licensee of a Low Power FM (LPFM) broadcast station, you are required by FCC rules to use a transmitter that has been specifically type certified for the Low Power FM service. These are transmitters that have been tested in a laboratory and meet specific federal specifications. These transmitters are made by the major manufacturers such as Nautel and BW. Even older Part 73 "type accepted" transmitters that do not bear the LPFM certification are not legal for use by LPFM stations and in no case are any of the transmitters sold on Ebay or through Chinese importers legal for use by a licensed LPFM station.
License-free operation in the FM Broadcast band
License free operation in the 88 to 108 MHz band is regulated by section §15.239 of the FCC rules. These rules specifically state that:
Emissions from the intentional radiator shall be confined within a band 200 kHz wide centered on the operating frequency. The 200 kHz band shall lie wholly within the frequency range of 88-108 MHz. This means that the transmitter follows the same standards for FM broadcasting and in no case shall a center frequency be either 88.0 or 108.0. 88.1 through 107.9 are the legal frequencies. Part 15 operation in TV Channel 6 spectrum such as on 87.7 and 87.9 is prohibited under 15.209(a) of the rules. This means ANY power on 87.7 and 87.9 is not permitted. Emissions within the permitted 200 kHz band shall not exceed 250 microvolts per meter at 3 meters. The emission limit in this paragraph is based on measurement instrumentation employing an average detector. (In other words, the output of the transmitter is based on field strength and not on power. Very regularly do we hear people think that the limit on FM is 100 milliwatts or a specific watt value. It's not. It is a combination of your power output and the efficiency of the attached antenna. Keep in mind that there is no restriction on antenna height as long as the field strength measured at 3 meters is 250 microvolts or less.)
The field strength of emissions radiated on a frequency outside the specified 200 kHz band shall not exceed the general radiated limits in §15.209. (The transmitter must be stable and must suppress any out of band emissions. A very common problem with illegal transmitters is that they produce spurious emissions in the spectrum used for aeronautical communications and navigation 108~136 MHz and thus can cause interference to safety of life communications. Despite the changes in FCC field enforcement, interference to aviation is still a huge priority at the Commission.)
In addition, all Part 15 intentional radiators such as very low power FM transmitters must have a FCC certification number on it. We have seen many cases where Chinese imported transmitters are using falsified certification numbers on them.
At REC, we currently operate the C. Crane FM-2 Transmitter. This is an agile transmitter (88.3~107.7 MHz) and puts out very clean sound. Using the built-in antenna and mounted on a high shelf on the second story of a wood house, we are able to get approximately 100 feet in all directions. This is the type of range that you should expect from a Part 15 certified FM broadcast transmitter. Most of the legal Part 15 transmitters marketed these days are intended to put the audio of a smartphone or MP3 player over a car radio and usually consist of a transmitter that is attached to a cigarette lighter plug or is battery operated and then a cord that plugs into the headphone jack of the smartphone or MP3 player.
We do note that even for a Part 15 transmitter with a registration number, that registration is automatically voided if any unauthorized modifications are made to the device. This includes increasing the output power higher than the factory setting, modifying the unit to add an antenna jack or otherwise modifying the antenna system in any way.
ILLEGAL FM TRANSMITTERS
Below are examples of transmitters that are being sold illegally in the United States. These transmitters claim to operate anywhere from a half watt (500 mw) to over 7 watts. While they may claim to be FCC legal, they are not:
Transmitters like the three shown above ARE ILLEGAL FOR SALE OR USE IN THE UNITED STATES, CANADA, JAPAN AND THE EUROPEAN UNION. These three transmitters were found on amazon.com. So even though Amazon fulfills these does not mean they are legal. Amazon's sales rules specifically allow for the sale of "low power FM transmitters" but because there are three different types of low power FM transmitters out there, it does not specify that those that are illegal for sale in the USA are not authorized to be sold on Amazon. Unfortunately, Amazon has turned a blind eye to this issue.