[ARC5] Re: [Milsurplus] Re: SCR-274-N Transmitter Dial Accuracy

[Jim Haynes]

I have a portion of the maintenance manual for the B-25 C and D
airplanes, published by North American Aviation.  It must be something
I found on the net, as I don't have a hard copy but a pdf.  The B-25
was pretty small as bombers go, but it had a full radio complement.
SCR-274N, 3 receivers and 2 transmitters for command, BC-375 and BC-348
for liaison, radio compass receiver, IFF set, marker beacon receiver,
and a BC-221 frequency meter.  The manual doesn't go into how all this
was used, so I don't know if the BC-221 was used only with the BC-375
or if it was also used with the SCR-274N transmitters in flight.
Those transmitters are in a rather hard-to-reach place, but then they
would be hard to reach on the ground as well as in the air.

It says the command receivers are BC-453, 4, and 5.  They are controlled
remotely from a 3-position box at the co-pilot's side of the airplane.
It says the transmitters are BC-458-A (5.3-7.0 mc) and BC-459-A
(7.0-9.1 mc) but that BC-457-A (4.0-5.3 mc) may be substituted for
either of these.  That's curious since the standard tower frequency
was 4495 kc, but then maybe the people at NAA writing the manual didn't
know all about it either.  Or maybe the standard tower frequency was
not all that standard.

It lists various models of BC-348 receivers by various manufacturers,
as well as 1TA20D by Stromberg-Carlson.  I had never heard of that one
before, but they don't say anything about it being any different from
the BC-348s.

The picture shows six tuning units for the BC-375, in addition to the
one in the radio.  There's also a trailing wire antenna.

Jim W6JVE

jhhaynes at earthlink dot net