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

[Michael Murphy]

Rich,

I have had a couple of the grey Air Force units and still own one of the
Navy units as shown in your picture. They did make great CW filters although
they were a little high in frequency for most CW ops taste. I used mine on
an 80M command set and on the BC-348 to get some CW selectivity back in the
1970's. Here is a link and an excerpt.

http://www.ibiblio.org/pub/academic/agriculture/agronomy/ham/BOATANCHORS/200
40731.ba.v03_n681

The Army Air Force chose to mount the filter remotely from the switching
function.  The Navy had a combined unit, which is very nice but larger that
the Army switch box.

The Army filter is the FL-5-* and the switch box is the BC-345.  They were
used at only the pilot's and copilot's positions along with the BC-366 Jack
Box.  Other crew positions had only the BC-366 Jack Box which provided
switching between the different communications systems and a place to plug
in a headset and a microphone.

The switch positions on the BC-366 were:

COMP - radio compass receive only
LIAISON - liaison radio receive and sidetone only for most crew members
transmit for pilot, copilot and radio operator
COMMAND - command set transmit, sidetone and receive available at all
stations
INTER - Interphone available at all crew stations
CALL - Overrides all other positions so that any or all crewmembers can be
called to switch to the intercom channel.  Spring return position

On the BC-345, the three positions are RANGE, VOICE or BOTH.  During the
war, weather reports were often transmitted on navigational beacons located
in frequencies below the broadcast band.  The navigation signals were MCW at
a frequency of 1020 cycles.  The original radio range navigation system
consisted of radio beacons that transmitted four beams roughly 90 degrees
apart although this was modified by adjusting the antenna pattern to provide
the desired courses.  The letter A was transmitted in Morse on one side of
the course and the letter N on the other.  These two Morse characters are
complimentary so that the on-course signal was a steady tone.  Depending on
which of the four courses from a particular beacon was being used the As
could be on the left or right side of the course.  Thus, it was necessary to
have a chart to tell which way you should turn to find the desired course.

The three filter positions allowed the pilot or copilot to hear either the
voice signal, the navigation (range) signal or both.

The only remaining vestiges of this system are now called NDBs (for Non
Directional Beacon) and can still be heard if you have a receiver that
covers the frequency.   Generally, they are in the 200-300 Kc range.  (there
were no Hertz in those days!)  There are no longer As and Ns but MCW
identification is transmitted along with voice information.

The Navy unit is simply called Radio Beam Filter stock no. (R) 16-F-2150.
It is a great little unit if you can find one.  It is in a nice, black
wrinkle finished case with a sloping front upon which is mounted the switch.
It also comes with a cord and PL-55 to plug right into your receiver's
output.

Lenox Carruth
WA5OVG

Mike Murphy WB2UID



----- Original Message -----
From: "Kenneth G. Gordon" <kgordon at moscow.com>
To: <RLucch2098 at aol.com>
Cc: <R-390 at mailman.qth.net>
Sent: Saturday, December 18, 2004 5:43 PM
Subject: Re: [R-390] Can you please help identify this?


> > 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
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