[Milsurplus] Fisher labs RDF

[C.Whitaker]

Mike,
Radio Direction Finders in aircraft did not work very
well at all on a four-course radio range facility.
The A's or N's kicked the needle all over unless you're
exactly on course. .
RDF's were required for an ILS approach, otherwise
wander around trying to come up on the LF Beacon
at the Outer Marker from the proper direction.  Compass
Locator, it was.   Watching the needle was better than
looking for the null, and figuring what to do next.
73  Clete