"Roy Smith" wrote in message
...
In article ,
"William W. Plummer" wrote:

... 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. ...

http://www.airwaysmuseum.com/Lorenz%20SYR%2044.htm

.... technically "4-course radio range"...and they were decommissioned as
soon as VORs and ADF receivers became prevalent. In Canada that was the
early-to-mid 1960's, with the possible exception of some isolated relic.

Anything is possible, but I don't think the OP picture is one of those.

Interesting to note, that even then (and how accurately could a course have
been followed???).... even then pilots were encouraged to fly
right-of-course to avoid meeting someone else "on course":
http://www.navfltsm.addr.com/ndb-nav-history.htm