[ARC5] ATA/ARA, SCR-274N, AN/ARC-5

[David Stinson]

(Requested information on " ARC-5 " set differences copied to list)

Originally nomenclatured GT / RBD, the Navy bought the 
first production, re-nomenclatured ATA / ARA, which used 
a screen modulationer and required a specific tuning procedure,
often flubbed in practice.
Receiver coverage was .19 to 9.0 MC spread over five receivers.
Transmitter coverage 2.1-9.0 MC spread over five transmitters.
First contract date June 1940.  Earliest acceptance test date 
in my database is Contract NOs-74912, Febuary 1942.  
Latest is Contract NXsa-53321, Aug. 1944.

Next was (at first) a partial copy of ATA/ARA by the Army
with became SCR-274N.   The Army had less money to spend.
Original order number 1470-NY-41 by Aircraft Radio Corporation, 
consisted of three receivers 
covering 190-550 KC, 3-6 MC and 6-9 MC.
Three transmitters covered 4-5.3, 5.3-7 and 7-9 MC.
A.R.C. 274N items are scarce to rare.
The 3-4 MC BC-696 was not introduced until one of the later
Western Electric runs, when the Army discovered that being able
to talk to all those civilian 3105 KC airfields might be useful.
The 550-1500 receiver for navigation use came-out mid-war.
SCR-274N units are not marked for acceptance test dates.
A stand-alone VHF version of SCR-274N with an internal
modulator was produced by Western Electric mid-war.  
Only about 1000 were made.  The VHF control boxes are scarce.
274N VHF TX-RX units are "rare."
Most were converted to AN/ARC-5 VHF and integrated into
the overall AN/ARC-5 LF-VHF system.  If your T-23 transmitter
has a tube-socket hole and two smaller holes punched in the
chassis near the front, which might even be marked "815,"
you have a BC-950 SCR-274N that was re-worked 
into a T-23/ARC-5.  No 274N VHF manuals 
are know to have survived.  I'd dearly love to find one.

AN/ARC-5 was an "improved" ATA / ARA (it was, in fact,
first nomenclatured "ATA-3" and "ARA-3" but no units 
are know to have been produced under that nomenclature.
The AN/ARC-5 transmitters used a plate modulator, which
eliminated the hinky tuning procedure, and other improvements.
The receivers were improved for AVC and stability issues.
Many, many accessories were produced and AN/ARC-5
was cobbled together in a bewildering number of assemblies,
accessories and contract numbers.
The receivers covered .19-9.0 MC in five units.
The transmitters originally covered 2.1-9.0 MC in five units.
Transmitters covering .5-2.1 MC in three units were added 
NXsa-32848 in January of 1944. 
Mid-war, Western Electric integrated VHF sets into 
the overall AN/ARC-5 system.
The earliest AN/ARC-5 acceptance test date 
in my database is Feb. 1943.   
Latest is (believe it or not) Sept. 1949.

There are rumors of a short production of tranmitters
for 9-15 MC, but no solid evidence. 
73 DE Dave AB5S