Radio engineers: Transmission/reception quandry

Factual Questions
1

I’m a fan of a particular radio station appx. 40 miles away (NPR; WOUB: Athens, Ohio) and to put it mildly, reception in our area is sketchy. Not to belabor a point but, “I’ve been around” when it comes to the eccentricities of radio reception from distant stations… It comes and goes, varying over time based upon many criteria… I understand.

However, the crux of my quandary is: There is a tiny “dead zone” for reception that baffles me, and this area seems to affect other, stronger stations as well that beam from entirely different directions.

Our part of the world is hilly: 250’ ridges are common and of which, I live on top of one. In my travel back and forth from home, I pass an area (on the ridgetop) app. 150 yards long in which a reasonably strong signal from my station drops out, and is supplanted by another (unidentified) station. ALWAYS, irrespective of time of day, weather, etc. There is nothing geographically noteworthy about this spot, it is essentially homogenous with the terrain (except for being high) for miles around. Directly below this area, is a “dead zone” known to all locals as the place where ALL radio dies, including local, (3-10 mile) strong signals, that arrive (or are transmitted, I know) from multi-directions. Again, nothing noteworthy in it’s geography.

I can’t explain away this weirdness by blaming radio stations’ transmission beaming patterns based upon their proclivity for change due to their target audience… It’s been like this for decades, and it is (reliably) un-varying! It has been my experience over the years that there is no one transmission pattern, (much less multiple patterns) that is such a lock-cinch deviant in one area.

Am I living on a mountain of iron, a secret NSA dead zone similar to Greenbank, buried UFO’s underneath, electromagnetic anomalies created by the tree commission?

2

This is the coverage map for your favourite station. WOUB-FM Radio Station Coverage Map

It is an FM station, so your main problems are going to be that:
reception is largely line of sight
reception can be subject to multipath interference.

FM signals are subject to an interesting phenomenon - a receiver locks onto only one signal at a given frequency. Unlike AM, where if you have multiple transmitters at the same frequency you get all the sounds overlain on top of one another, an FM receiver simply selects the strongest. If your current station is on the same frequency as another weak signal, you will hear your station, unless its signal drops out, in which case the weaker signal will suddenly become heard.

Multipath problem are due to destructive interference of the signal due to various reflection of the signal leading to the signal arriving from multiple directions and taking a longer path on some of them. Built up areas have a problem with reflections off buildings, and hilly areas have problems with reflections off terrain. Edges and ridges also cause multipath problems as the wave diffracts around the edge. It may be possible your ridge is in a particular spot where these effects are conspiring to wipe out reception and leave you with a signal from a much further away station that you would not normally hear.

3

Interesting: Although my situation doesn’t seem to apply, I’ll investigate.

4

I briefly considered interference effects, but it sounds like the dead zone the OP is describing is much larger than the wavelength, so that wouldn’t work (especially with irregular reflectors like natural terrain).