In article ,
"William W. Plummer" wrote:

Could it be an old OMEGA system. That was decommissioned only about 5
years ago. As I understand it, this was the original radio navigation
system for airplanes know as "Highways in the Skies". It was low
frequency. The pilot would listen to the selected frequency and hear a
steady tone if he was right on the highway, or di-dah ("A") if on one
side or dah-dit ("N") on the other.

I think you're talking about the old 4-course airways. OMEGA was a
hyperbolic radio navigation system (in some ways similar to LORAN). It
was used by both aircraft and ships for trans-oceanic navigation, with a
fix accuracy of about 4 nm (you can do better with a sextant).

There were only 8 transmitters in the world (and the one in the US is
still in use for other purposes), so it seems unlikely that much surplus
equipment would be available. Transmission was in the 10 kHz band.

http://webhome.idirect.com/~jproc/hyperbolic/omega.html