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What is the highest legal power for an FM radio wave generator in the United States? Answered

I am building a project that transmits FM radio waves about a mile with frequencies capable of being picked up by a normal FM radio. I know that those little iTrip connectors for the iPod can legally generate FM signals capable of being picked up by a car's radio antenna, but a mile of transmission seems a bit excessive to me. Would such a device be illegal? Does anyone have any links where I can find such information? Thank you.



Best Answer 6 years ago

100KW FM Power as per the FCC
Federal Communications Commission

It took a minute to find this :)


While iceng is technically right, that does not mean, you can legally go and build a 100kW FM transmitter. First, the 100kW are ERP (effective radiated power), meaning the power of the transmitter minus any losses in cables plus the gain of your antenna. Second, that website is for licensed broadcasting stations. Those little iPod transmitters are maybe not even legal where you live but are tolerated because they just transmit in the mW range and only affect a very small area. With a transmitter that spans a mile, you might break several laws, jam some licensed radio transmissions (even on other frequencies, if your transmitter isn't very well designed - IM3 problems and such...) and you might have some cars with strange antennas in your front yard.

Really? I recall there being a 320KW radio station near Grand Rapids...

Okay, there seems to be a 320KW ERP transmitter.

So what? They might have been grandfathered to an older law, got an exemption for whatever reason, etc.

The OP wanted to transmit over a mile. Less than ten Watts should be sufficient for that distance. The bigger problem is that he/she will be broadcasting as anyone can tune in on that frequency. For this, a broadcasting license is needed in most jurisdictions.