[Boatanchors] FL-5-F

[Jim Haynes]

On Thu, 14 Aug 2014, D C _Mac_ Macdonald wrote:

> Is it a smallish diecast aluminum box with a three-position switch? If so, it's most likely an audio pass and/or reject audio filter centered on 1020 Hz. Used in WW II and Korea vintage military aircraft.
>
If I remember correctly, what you are describing is the later FL-8.
The FL-5 had the filter in one diecast box and the switch in another
box.

The three-position switch was labelled RANGE-VOICE-BOTH
In the RANGE position the filter is a narrow bandpass filter centered
on 1020 Hz.  In the VOICE the filter is a narrow band stop filter
centered on 1020 Hz.  And in the BOTH position the filter is out
of the path between receiver output and the airman's headphones.

For the way it was used see the wikipedia article on low-frequency
radio range.  The filter allowed the airman to hear only the A-N
range signal, or only voice announcements such as weather broadcasts
and ground-to-plane communication, or both.