[ARC5] WWII-Era VHF Command Set Frequencies and Crystal Information (plus survival radios)

[Mike Morrow]

Ken wrote:

> However, I thought the GC (Guard Channel) frequency was always set 
> to 121.5 MHz, the emergency frequency.
>
> At least the ARC-1 I got from AFMARS back in the 1960s had that 
> installed there...

The first VHF frequency that became a guard and/or emergency channel
was 140.58 MHz.  That's what you'll find on all the WWII-vintage VHF
sets (even USAAF).  It's channel 1 (P-P) on the AN/ARC-4 (likely
the first VHF set that had a guard channel), and channel C on the
AN/ARC-5.  The AN/ARC-5, and the USAAF SCR-522-A and AN/ARC-3 did
not have a guard channel that could be monitored while another
channel was active.  The R-67A/ARC-3 was modified to have an input
to its IF string for a proposed external guard receiver, but I've
never seen any indication that such an addition was ever made.  The
new UHF-AM command sets (like the AN/ARC-27) most likely eliminated
any concern about monitoring a VHF guard channel by the military.

Sometime after WWII, 121.5 MHz was established as a standard
emergency channel, primarily for civil air use, while 243.0 MHz
became standard for military use.  Both of these frequencies
are multiples of 40.5 MHz, which became the military's tactical
low-band VHF FM emergency/guard frequency.

All these older sets still in service would later have been altered
from 140.58 to 121.5 MHz.  I have another RT-18/ARC-1 with the guard
channel on 121.5 MHz.


Diversion of topic follows:

The earliest military survival radios were the SCR-578-A and
AN/CRT-3 "Gibson Girl" sets.  These were transmitters only on
500 kHz A2 (and 8280 kHz A1 for the AN/CRT-3).  The USAAF added
the Setchel-Carlson Model 591 dry-battery beacon-band receiver as
the AN/CRR-1 to the SCR-578-A to enable two-way communications
with the distressed party, allegedly for arctic use.  I suppose
that suggests one use for aircraft transmission capability in the
beacon-band.

The early pocket-able survival radio, the AN/CRC-7, operated on
140.58 MHz.  Sometime after WWII, but before the Korean War, the
well-known 121.5 and 243.0 MHz standards were established.  The
next pilot survival radio, the AN/PRC-17, -17A, was made during
the Korean War and could operate on 121.5 or 243.0 MHz, determined
by a control switch on the side.  A little later, the RT-159*/URC-4
became standard everywhere and could operate on 121.5 or 243.0 MHz.
That was replaced by the RT-285*/URC-11 for 243.0 MHz only, plus there
was the nearly identical RT-350*/URC-14 for 121.5 MHz.  I've never
seen any indication the the military ever used the 121.5 MHz version.
The ones I've seen have no federal contract or order numbers on them.
But I know some airlines like PanAm carried the AN/URC-14 in the
civilian airliner's emergency equipment!

Mike / KK5F