Is it legal to use uncertified AM/FM 100 mW transmitters for hobby broadcasting? I read somewhere that it was legal if the operator observes the "color of rule" as it related to the FCC's guidelines governing Part 15's. Let me know, thanks...
It is not legal to use a 100 mw FM transmitter, certified or not without a license. Current the FCC does not license any FM operating below 100 watts.
As far as AM, 100 mw is legal certified or not. One may not sell a pre-assembled AM transmitter without it being certified. Kits or home brew OK as long as the power does not exceed 100 mw and the combined length of antenna and ground lead do not exceed 3 meters.
Actually there is no rule regarding an FM TX and its power output. The only rule is the field strength limit of 250uV at 3 meters from the antenna.
The idea is to operate an FM TX that has been approved with certification. Safe all the way around. But that does not mean you are limited to that. If you can show that the field strength is 250uV 3 meters from the antenna, it does not matter if your using a 1 or 5 or 10 or 100 or even a 20Kw TX.
It is a lot like owning a gun. I can own a Harris FM 20 20Kw transmitter. I just cannot run it into an antenna system that causes it to radiate that RF energy. I can run it into a dummy load all I want and rack up a nice fat utility bill. I can run that into the dummy load and tap a tiny piece of that signal and feed it to an antenna with attenuators and if that signal coming off that antenna is 250uV at 3 meters, its perfectly legal, though hard noses would bang their feet on the floor and frown because they believe its too much box for the job. It is too much box for such a little job, but there is no rule saying I cannot have a big box. And just like the gun, there is no rule saying I cannot have one or use it. How I use it does define legal or not.
For the MW band, the rules clearly specify the power level and antenna system specifications.
As to the sales and marketing, I think that is nothing more than putting a thumb on economic growth and nothing to do with the spirit of the technical rules and specifications for good engineering practices or serving the public interest.
RFB
"Actually there is no rule regarding an FM TX and its power output. The only rule is the field strength limit of 250uV at 3 meters from the antenna".
Always love your posts and obvious knowledge of these matters, RF. Your interpretation is exactly what I deduced after reading the Part 15 rules for FM You're the 'Man of the month" it seems in the forum it seems. Lol.
And really under Part 15.209, I could run a 50 KW Blowtorch on the AM band-into a dummy load and sniff out the power to an antenna that stays within the specified field strength.
If you can successfully contain that 50Kw "blowtorch" in the AM band into a dummy load tapping it with the 219 3 meter schtick and maintain that specified field strength I would like to see just such a setup! :p
Don't forget, the Part 15 rules for the MW band are combined with 209, 219, and 221. So no....you cant, not into the 3 meter schtick.
Run into a dummy load, then through one hell of an attenuator to drop that down to 20 watts or so, then into a coupler for CC and your fine. But now let me play the role of a hard nose feet stomping critic......TOO BIG A BOX FOR THE JOB!! :p
Not to mention an even FATTER electric bill!!
Added later comment: LOL!! I get a kick out of the use of "blowtorch" when the 50Kw number is tossed out there.
HAHAHAHA! pfft.
RFB
"Always love your posts and obvious knowledge of these matters, RF. Your interpretation is exactly what I deduced after reading the Part 15 rules for FM You're the 'Man of the month" it seems in the forum it seems. Lol."
Much appreciated. I do not stake any claim to knowing it all, but I think after 30+ years in the broadcast engineering industry I should know a little something about it! 😀
RFB