I'm not sure that the proposed test protocol is going to produce much useful data, at least for FM: with the ready availability of cheap IF stages with built-in AGC, I don't think that there's such a thing as a "simple FM receiver" anymore (except maybe in thrift shops) (;-). Even the cheesiest penny-a-pop single-chip AM receivers have some flavor of AGC these days, seems like... Anyway, once you get past a pretty low threshold signal level, the AGC (if present) will flatten out any incoming signal strength variations and mask much of the change you seek to measure. AM will work better than FM for this test- but it sounds like his problems are likely to be 100MHz and up, from his description of the signal source as TV-only.
Yo, Brian- got any ham buddies who could be persuaded to make a few measurements in exchange for a few beers? I've never known a ham that didn't have at least a gnarly old grid-dip meter, and you can actually do some pretty decent differential field strength measurements with one with some practice. I've also never known a ham that didn't like beer! Otherwise, it's a right bitch to really calibrate this stuff.
5 miles from the tower is a goodly distance. All I can say is "be very glad for that!". From your initial postings, I thought that you were much closer in. The inverse-square law works very strongly in your favor: 5 miles buys you a *lot* of quiet, compared to 200 yards. So does having the objectionable signal be FM and 100MHz and up, as opposed to 740 kHz AM!
Reminds me of another story from my misspent youth. I was putting a pre-announcement consumer product through its mandatory FCC Class-B EMC testing at a commercial EMC range back in Massachusetts. This was early in my career, just a couple of years after that WBZ fiasco. The test facility was really good, and very well-equipped, but their location just outside Boston had a noise floor that was significantly *higher* then the Class-B limits in a lot of places during normal daytime hours! We had to do the bulk of the compliance measurements on their range between 1:00 and 4:00am, and there were a number of chunks of the spectrum that were still masked anyway, and had to be handwaved...
Best of all- there was a welding shop about half a mile away that used pulse-TIG to perform nuclear-quality welding on 1/2"- 1" steel, and when they'd strike an arc on the heavy-duty stuff the whole spectrum from about 100kHz to about 500 MHz would just be solid trash: the spectrum analyzer display would just white out. Drove the EMC test lab guys absolutely _bugfuck_ when the welders would work late, since they weren't making any money when the range was full of hash. And that kind of pulsed-broadband source is just about impossible to effectively screen against to Class-B levels, even if you're the pro's pro. I think they finally moved up into rural New Hampshire in self-defense.
Be glad your studio ain't next door to those guys, too! Anyway, good luck with the rig, and hopefully you will be able to get some meaningful before and after data on your screening job. It isn't going to be easy, though.
