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There are two Ramsey units. FM-25A and FM-25B.
I have the A unit and it is difficult to get this to work well without hum. Mine is just fine after I enclosed it an a metal box. I don’t have a B but from what I read it is better than the A.
As far as compliance goes, the rules set a limit on the field strength. It is impossible for a user to measure this so you have to rely on the manufacturer’s guidance, especially on the antenna to use.
The Ramsey unit is not certified but that doesn’t mean it is not compliant when used with the correct antenna. Even if you get a certified transmitter it has to be used with a particular antenna which the manufacturer provides to insure compliance. Use of any other antenna voids certification.
If you do get the used unit, the FM-25A has a jumper inside which will have to be removed else you will be way over the legal limit. I don’t know if the B has the same jumper, just be aware of it. The manual will tell you about this.
With all that said, practically if the transmitter can be heard about 200 feet away, and not much more, then it is probably compliant and you won’t have problems. Trouble happens when people extend their range using high power or long antennas and greatly exceed the FCC limits.
Sorry if this seems complicated. Just limit your range as mentioned, don’t cause interference and you will be OK.