[ARC5] WWII-Era VHF Command Set Frequencies and Crystal Information

[Mike Morrow]

U.S. Navy - Operating Frequencies Supplied In New Sets

                                  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     142.46       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


U.S. Army - Operating Frequencies Supplied In New Sets

                                  Receiver    Transmitter
           Channel  Freq. (MHz)     Crystal Freq. (kHz)

SCR-522-A                         BC-624-*    BC-625-*
             A       Unknown
             B       Unknown
             C       Unknown
             D       Unknown
Equipment Operating Frequency Range:  100 to 156 MHz
Crystal Type:  CR-1A/AR
Receiver Frequency MHz = Crystal Frequency kHz x H / 1000 + 12
   Receiver Frequency    H (Local Oscillator Harmonic)
       100 to 108                  11
       108 to 116                  12
       116 to 124                  13
       124 to 132                  14
       132 to 140                  15
       140 to 148                  16
       148 to 156                  17
Transmitter Frequency MHz = Crystal Frequency kHz x 18 / 1000

AN/ARC-3                        R-77*/ARC-5  T-67*/ARC-5
             A       Unknown
             B       Unknown
             C       Unknown
             D       Unknown
             E       Unknown
             F       Unknown
             G       Unknown
             H       Unknown
Equipment Operating Frequency Range:  100 to 156 MHz
Crystal Type:  CR-1A/AR
Receiver Frequency MHz = Crystal Frequency kHz x H / 1000 + 12
   Receiver Frequency    H (Local Oscillator Harmonic)
       100 to 108                  11
       108 to 116                  12
       116 to 124                  13
       124 to 132                  14
       132 to 140                  15
       140 to 148                  16
       148 to 156                  17
Transmitter Frequency MHz = Crystal Frequency kHz x 18 / 1000

Comment:  This is a gratuitous posting to summarize the crystal versus
operating frequency relationships of all the common U.S. military
aircraft VHF sets of the WWII era.  

Also listed are the frequencies supplied with new equipment for U.S.
Navy sets.  I only recently determined the AN/ARC-1 supplied frequencies
after I examined a NOS AN/ARC-1 (yes, it still has the rare auto-tune
setting dial tuning device) that has an early WWII contract number and
all identical-make crystals for the early VHF-AM frequencies used by the
military in WWII.  I think this set may somehow have escaped use because
the nomenclature decal that Westinghouse applied to it says C-45/ARC-1
rather than the correct RT-18/ARC-1.  Sometimes simple errors like that
can alter a set's usage, causing it to be withheld from issue or use.

I don't have enough information on new USAAF VHF sets (except the 
48-channel version of the AN/ARC-3 known as the AN/ARC-49) to know
for sure if they came from the factory with crystals for some standard
channels already installed.  (The AN/ARC-49 did.)  I'd like to hear
from anyone who has such information. The USAAF continued use of VHF
command sets long after WWII (while the USN quickly abandoned VHF in
favor of UHF), so there is little chance that an SCR-522-A or AN/ARC-3
found today with all military-use crystals still installed would
reflect what was there when the unit left the factory.

Looking at the various formulas relating crystal frequency to operating
frequency, and also crystal types, one finds little consistency between
the USN's AN/ARC-1, -4, and -5 VHF sets.  The USAAF sets, however, used
exactly the same relationships and crystal types for the SCR-522-A and
the AN/ARC-3.

Mike / KK5F