> > I haven't seen it mentioned yet, but yes, this sounds like a classic > case of Intermood.
I don't think it is classic intermod. Think about it. The deviation of the broadcast station is 75 kc. A signal that wide <cannot> be heard in a receiver designed for 5 kc., except, maybe, VERY distorted, and even then, the squelch circuit usually will not open with such a signal present. I've dealt with FM broadcast intermod on a repeater that I maintain. This one is the classic A+B-C formula. 89.9 + 147.06 - 89.3 = 147.66. Yes, this produces a signal on our 7.66 input, but is VERY wide. It does not manifest itself until, and only until, both broadcast stations have no modulation on them at the same time. Only then does the intermod product become narrow enough to stay within the passband of our receiver and be heard. The instant either broadcast station begins modulating, our squelch closes, and the intermod is not heard. I've traced the mixing to the tower guy wire anchor area. Tower riggers weave cable through the turnbuckles. This creates numerous places where metal is barely touching and rubbing, a great place for mini-diodes and just plain scratching noise too. Placing sections of vinyl insulation in problem areas cures the problem here. > > Best wishes, > > Dick, W7TIO (retired Mobile Radio Communications tech.) > > Ken Laryn K8TVZ
