[R-390] Can you please help identify this?

[Kenneth G. Gordon]

> I know the name marked is Beam-Finder.
> Seems to be an Audio filter & works nice.
> Any ideas?
> Pics:
> http://www.myradioroom.com/navybeam-finder1.jpg
> http://www.myradioroom.com/navybeam-finder3.jpg
> Tnx & 73..
> Rich WA2RQY

Hi, Rich:

BTW, I have your tubes (VT-131) all packed up. Line at the USPS is 
about a mile long, so will mail this asap.

What you have is a "Beam Filter". It was normally used by aircraft when 
listening to the "Radio Range" stations. Most of those have been taken 
over, BTW, by the NDBs of today.

Those Range stations, transmitted both a VOICE signal, usually 
recorded information on weather or landing conditions at the airport 
where the Range stations was located.

In addition, they also transmitted an MCW signal, usually at 1020 Hz, 
which, depending on whether or not you were to one side or the other 
of the path directly towards that station, was either the International 
Morse Code letter "N" or "A". When you were directly on the path to the 
station, you got a steady carrier, and also when you passed directly 
over it.

The Beam Filter was used in the "RANGE" position to filter out the 
voice signal, leaving ONLY the 1020 Hz "A", "N", or the steady carrier. 

Hams used it to peak up a CW signal.

In the "VOICE" position, it filtered out the 1020 Hz "RANGE" signal so 
you weren't bothered by that 1020 Hz noise when you were trying to 
copy the voice signal.

Hams used it to remove an annoying heterodyne on a voice signal, if 
there was one at the right frequency: 1020 Hz.

In the "BOTH" position, it bypassed the filter completely so that you 
heard both signals. This position was a bit more sensitive than either of 
the other two, so it was normally used when listening for a weak station.

Hope this helps.

Ken Gordon W7EKB