Total posts : 45366
It’s easy to see where the 100 mw on FM myth makes a ton of enforcement headaches for the FCC. And, to be honest, probably results in a whole lot of people getting in trouble who honestly were *not* trying to be “pirates”.
If the “250uV/M at a distance of 3 meters” wasn’t something that was so nearly impossible for a hobby level person to check, it might be easier to clear up that misconception. But people who want to build an FM transmitter, whether to save money or for the learning experiences and “built it myself!” pride, are basically up the creek without a paddle. No way to test it with anything like common instruments to confirm compliance. So it’s not hard to understand why they prefer to believe it’s something that is enough that they *can* measure.
Even buying one, there are a ton of places on the net selling stuff as “part 15 FM” that isn’t certified and where the stated power for what they’re calling part 15 could get someone in a lot of trouble.
My usual advice to people interested in part 15 FM is buy a certified transmitter and also to check the FCC ID against the FCC database and look at pics and etc to confirm that it *is* the transmitter the ID # goes with. And use it just as it comes out of the box. If you want to build and tinker, build and tinker audio gear and cool accessories for your station. Much as I hate to say it, it just isn’t worth the risk to build the transmitter in my opinion.
That isn’t just talk, I started with a transmitter I built from a kit. As a result of conversations on this and other boards and asking questions, getting answers and learning more, I retired it permanently in favor of a commercial certified transmitter.
There is the occasional mention of the small but existent possibility that a certified transmitter might still, due to multipath effects, appear to put out as much as 2 or 3 times the allowed power if it was placed “just exactly wrong” in regards to local terrain and etc. But if you look through the FCC field actions, I doubt you’ll see any actions involving stations putting out power in that range. Most of the NOUO, NAL and etc are for stations putting out at least several hundred times the amount that any actually legal certified Part 15 FM transmitter could. But those violations could easily happen with a “25 mw” or “10 mw” unit.
But a whole half a watt? Even into a random length piece of coathanger wire that would almost certainly put out far more than the legally allowed amount. Definitely enough to get busted for. If by some miracle it was actually low enough output with the antenna chosen that it was at legal power.. You’d still probably have spent a lot more for it than you could have for some certified units.
You can buy a C. Crane for under a hundred, and some certified FM part 15 transmitters can be bought (fully assembled) for as little as 20$.
Take any advice you find here or elsewhere as you will. But try to remember that it’s *your* fanny and the people handing out advice aren’t the ones who’d end up paying your fine if you get a NAL.