[ARC5] AN/CRC-7, and Other VHF Use

[Mike Morrow]

Jay wrote:

> Wouldn't 140.58 MHz have to be an implemented guard frequency before
> the AN/CRC-7 could be deployed? When did that take place?

It appears to have been the guard/emergency frequency in military VHF
sets from the earliest time that VHF command sets were used in US service.
I do not know if the pioneers in that field, the UK, had that as their
standard from the earliest time, but I do have some USAAF ETO documents
that indicate this frequency's usage by the USAAF as an emergency frequency
as well.

Post-WWII, it was eventually replaced by 121.5 MHz.  But I know that the
AN/CRC-7 was still being used in carrier based aircraft in the Korean War.
Unless they had been depot refurbished (and in some sense, redesigned)
for 121.5 MHz, that would mean that 140.58 MHz was still in use seven years
after WWII.  (There were many complaint about the batteries.)

> The crystals I have for the AN/ARC-4 include 140.58 MC, Western Electric,
> 703A Crystal unit.

That is the Western Electric crystal unit type.  The commercial model of the
RT-19/ARC-4 is the W.E. Model 233A.  In the military models, channel 1
(plane-to-plane) is the guard channel, on 140.58 MHz.

All USN VHF radio sets left the factory with crystals for 140.58 MHz.
Here's a excerpt from a posting I made in November 2011 that lists
the frequencies found in brand new sets:

--BEGIN EXCERPT--
                                  Receiver    Transmitter
           Channel  Freq. (MHz)     Crystal Freq. (kHz)
AN/ARC-1                               RT-18/ARC-1
              1      116.10              5910.00
              2      124.38              6370.00
              3      126.18              6470.00
              4      128.70              6610.00
              5      142.02              7350.00
              6      142.56              7380.00
              7      142.74              7390.00
              8      144.36              7480.00
              9      146.16              7580.00
             GC      140.58              7270.00
Equipment Operating Frequency Range:  100 to 156 MHz
Crystal Type:  CR-1A/AR
Operating Frequency MHz = Crystal Frequency kHz x 18 / 1000 + 9.72

AN/ARC-4                               RT-19/ARC-4
           1 P-P     140.58       8161.25     5857.50
           2 P-G     142.02       8251.25     5917.50
           3 P-G     142.56       8285.00     5940.00
           4 P-G     142.74       8296.25     5947.50
Equipment Operating Frequency Range:  140 to 144 MHz
Crystal Type:  WECo Type 703A (Dual Crystal Unit)
Receiver Frequency MHz = Crystal Frequency kHz x 16 / 1000 + 10
Transmitter Frequency MHz = Crystal Frequency kHz x 24 / 1000

AN/ARC-5                         R-28/ARC-5  T-23/ARC-5
             A       116.10       4550.00     6450.00
             B       126.18       4970.00     7010.00
             C       140.58       5570.00     7810.00
             D       142.74       5660.00     7930.00
Equipment Operating Frequency Range:  100 to 156 MHz
Crystal Type:  Receiver - DC-31   Transmitter - CR-1A/AR (DC-30)
Receiver Frequency MHz = Crystal Frequency kHz x 24 / 1000 + 6.9
Transmitter Frequency MHz = Crystal Frequency kHz x 18 / 1000
   Transmitter Channel Allowable Frequency Ranges
      Channel    T-23/ARC-5       T-126/ARC-5
         A       100 to 124       100 to 124
         B       122 to 146       100 to 124
         C       122 to 146       100 to 124
         D       132 to 156       122 to 146
--END EXCERPT--

> In that light was there any pre-WWII manufacture of distress radios
> for 140.58 that may have developed into the AN/CRC-7?

None that I know about.

> When did civil aviation begin using VHF as standard along with LF/HF?

Just after WWII, with a phase-in that lasted into the mid-1950s for
general aviation.

> When did this frequency become a military use frequency?

It was from the outset.  I suspect every SCR-522-A had this frequency,
so that would indicate late 1942 or so.  The USN also used the some
SCR-522-A sets.

Mike / KK5F