When I am not playing audio through my C.Crane FM3 but only hearing the carrier at 87.5 MHz there is a distinct musical beat heard in very smeary sounding way, which I believe is the power of a local radio station being absorbed in the transmitting antenna and mixing with my carrier.
Station by station I compared the screechy sound to every dial position and found a match at 98.1 FM, a 90 kW station not too far away. Why only this station and not various others located as closely is baffling.
RF works in mysterious ways!
That particular station could be causing interference by the way of not necessarily a harmonic but a spurious signal that is getting into 87.5 on your transmitter.
If you had a spectrum analyzer that takes signals off the air and check that station at 98.1 and see if there's a corresponding spike at 87.5, or even a good scanner would tell you this, you would have the answer.
They can cause interference but us...no no! That would explain why that station causes this but others don't.
Matter of fact I do have two spectrum analyzers!
Once all my other issues tone down a bit I'll look to see what the 98.1 station is up to.
@carl-blare The FCC says that the CCrane transmitter must accept any interference that may affect it's operation. It's doing what it's supposed to do!