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.
REC recommends SCMS as a source for compliant LPFM transmitters for the licensed service.
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 millivolts 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.
License free AM operation in the USA
While legal license-free FM may seem extremely restrictive, license free AM is slightly less restrictive.
Part 15 AM operation is regulated by section §15.219 of the FCC rules which state:
- The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed 100 milliwatts. (Unlike FM, we are talking power here. That power restriction is one-tenth of one-watt.)
- The total length of the transmission line, antenna and ground lead (if used) shall not exceed 3 meters. (The antenna and feedline can not exceed 10 feet. The ground system is considered part of the antenna system.)
- All emissions below 510 kHz or above 1705 kHz must be attenuated at least 20 dB below the level of the unmodulated carrier. Determination of compliance with the 20 dB attenuation specification may be based on measurements at the intentional radiator's antenna output terminal unless the intentionally radiator uses a permanetly attached antenna, in which case compliance shall be demonstrated by measuring the radiated emissions.
A certified Part 15 AM transmitter such as the Hamilton Rangemaster AM-1000 is the best way to go if you wish to go AM. This is a rugged unit that designed to be mounted outside. The AM-1000 uses a 102" CB radio whip for the antenna. You then match the antenna to your operating frequency.
For operations on AM, REC recommends that you use the expanded AM band between 1620 and 1700 kHz. There are fewer stations in this band day and night. In addition, the higher frequencies allow for short antennas as those allowed under Part 15 to better match up with the transmitter in order to provide the most efficient match.
While your results may vary, some Part 15 AM operators have reported ranges exceeding one mile with the legal configuration of the Part 15 AM transmitter and antenna. Your results may vary based on your antenna, time of day (expect shorter range at night) and even factors like ground conductivity and interference from adjacent channel stations. Also, the AM broadcast band is more susceptible to noise from all of the modern electronic gadgets that have entered the marketplace over the past couple of decades. Keep that in mind when considering to operate on AM.
Just a reminder, operating on 1,710 kHz is outside of the AM broadcast band and therefore is subject to more restrictive rules in contrast to those mentioned here.
License-free low power FM/AM device use in other parts of the world
|Canada||FM devices may not exceed a field strength of 100 microvolts at 30 meters. AM devices are limited to 250 microvolts at 30 meters. All devices in Canada must have an antenna permanently attached to the transmitter. See Industry Canada BETS-1.|
|CEPT nations including the European Uniton||FM falls under the "Wireless Audio" provisions of CEPT/ERC/REC 70-03 which calls for a maximum 50 nanowatt (0.00000005 watts) maximum ERP. Russia restricts transmitters to enclosed locations such as buildings and vehicles. There are no provisions for AM.|
|Australia||FM is limited to 10 microwatts. See ACMA Radiocommunications (Low Interference Potential Devices) Class License 2015.|
|Japan||AM and FM is limited to 500 microvolts per meter at 3 meters under a blanket regulation for all spectrum below 322 MHz. See MIC Regulation of the Extremely Low Power Radio Station (English). Our interpretation of the law also states that devices must bear the Technical Conformity Mark in order to be legally used in Japan.|
|Brunei||FM: 60 dBuV/m at 10 meters. AM: 57 dBuV/m at 3 meters.|
|China||FM: 3 milliwatts ERP. 84~87 MHz allowed 10 milliwatts ERP. Type acceptance required.|
|Hong Kong||None specified.|
|South Korea||500 microvolts per meter at 3 meters. (similar to Japan)|
|Malaysia||FM: 50 mW EIRP|
|Mexico||Any short range device used within Mexico must be certified by the Instituto Federal de Telecommunicaciones (IFT). Based on an REC consultation with IFT in 2016, it is not clear whether IFT will certify a short range device on 88~108 MHz or in the AM band for use in Mexico. Unlike in the CEPT areas and other jurisdictions, Mexican documentation on short range devices does not address the broadcast bands. Due to the lack of a specific standard for short range devices in the broadcast bands, we must also assume there is a prohibition on "home brew" devices. Our consultation will continue and we will update if new information surfaces.|
|New Zealand||"Audio senders" are allowed 0.00002 mW EIRP on 88-108 MHz. There is also an unrestricted allocation on 107-108 MHz for 25 mW EIRP. This is not to be confused with New Zeland's LPFM General User License that allows stations to broadcast up to 1 watt EIRP on specified spot frequencies in the FM band without having to obtain a broadcast license.|
|Singapore||AM: 57 dBuV/m at 3 meters. FM: 60 dBuV/m at 10 meters.|
|Vietnam||FM: 3 microwatts ERP|