Since I was a kid (I found KAAY when I was nine), I've twiddled the radio dial, chasing after stations in the distance- hence, the Ham radio term, "chasing DX". No matter what aspect of the hobby I've been involved with (I now hold an Extra Class Ham radio license), my first love has always been scanning the AM dial. Right now, my pet project is trying to identify a particular station on 1550 which has been playing classic rock music (The Guess Who, Starship, etc.) with pretty good audio. It seems as if, just as there might be a station i.d., there is a static crash from lightening or the signal fades...and, to make it worse, I can only hear the station for a few minutes in the afternoon around dusk, local Central time!
The "grey line" mentioned above is not the hairline of most of us here today! It is a tool, used by shortwave, mediumwave, scanner and other monitors/listeners and Ham radio operators to hear stations not normally on the air or possibly "covered up" by stronger stations.
Note that we hear radio signals by things that happen high in the atmosphere. There are what's called the "E layer" and "F layer" portions that are affected, but we'll concentrate on the "F layer" for this discussion. During the day, when sunlight strikes the "F layer", it splits into an "F1 layer" and an "F2 layer". This allows more of the radio signals to pass through and into space. At night, however, the reason why we could hear radio stations over longer distances and with greater strength, is that the "F1" and "F2" layers recombine, hence are more dense, and reflect MORE signal back to earth for our enjoyment!
This is where the "grey line" comes into play. There are some stations that shut down at sunset and come back on at sunrise; there are still others that reduce their power at sunset and resume full power at sunrise. The "grey line" lets one see where this dusk or dawn condition occurs and allows the listener or monitor to target certain areas of the country (or the world) to listen for stations they wouldn't normally hear. So, if you're in, say, Houston, TX and want to try and listen for a particular station in Michigan, the "grey line" map allows one to watch for the best time to listen!
Here's a link to this interesting tool:
The aforementioned station on 1550 fades in, then out in this small sliver of time along the "grey line". Not only does time hamper my efforts, but two other stations fade in and out about the same time: one, with a Christian praise/gospel music format, the other with a Hispanic music format. Due to the pretty decent audio of my target station, I feel lthat I need to learn the station's i.d. and compliment them on their good audio and fine selections of music!
Let me know if this helps you in hearing something you haven't heard before. I knew that something was up, even 'way back when, before I knew what "grey line propagation" was when KAAY would come booming in sometimes 30 minutes before dark!
And, the original blame for my current obsession with this station on 1550 goes to Ron H., for his post on AM audio- thanks, Ron for a fun obsession and a target to reach!
Bud S. (firstname.lastname@example.org)