[ARC5] Crystals in WWII

[Mike Morrow]

Wayne wrote:

> I always thought it quite odd that so much US WWII equipment used a crystal 
> to manually tune a VFO to the correct frequency.

To what equipment do you refer?  I can't think of many except the 'command sets',
and that was only indirect.  The cal crystal just verified dial calibration,
not the that the transmitter was set to a particular frequency.  The 0-4/ARC-5
could have been used with different specific crystals to set a command transmitter
to that frequency, but that doesn't seem to often have been used in that manner.

Transmitters that were not crystal controlled used a calibration or crystal
frequency indicator (CFI) as the device most often used to set the frequency
of receivers and transmitters.  The most common CFIs are the USN LM-* and
Signal Corps BC-221-* frequency meters.

> ...crystal distribution was found to be an unexpected nightmare, leading to the
> design of the ARC-5 series with VFOs.

Only the VHF models, though Gordon White discussed some attempts to produce
crystal controlled MF/HF command sets in CQ, September 1971.  The A.R.C. VHF
transmitter project produced no legacy for a future set.  AN/ARC-5 VHF gear
is a legacy of Western Electric's BC-942-A and BC-950-A crystal controlled
four-channel VHF sets for the SCR-274-N.  But before that, Western Electric
was working on a crystal-less VHF set for the SCR-274-N, using the BC-695-T1
receiver and the BC-699-T1 transmitter (discussed by Gordon White in
CQ, February 1976).  This was WECO's competitor to A.R.C.'s R-112 and -113
and T-89 and -90/ARC-5 crystal-less VHF set.  

> Or did they design the other military sets for VFO and then ended up using
> crystals because production caught up to demand and they were available?

I don't recognize any sets that fall into that category.  The tunable VHF
sets from A.R.C. and WECO discussed above were abandoned in favor of the very
different WECO crystal-controlled set, doubtless enabled by better crystal
supply.  The tunable VHF tactical FM set SCR-808/828 was abandoned after
limited deployment once crystal supply for the earlier SCR-508/528 was no
longer a problem.  Is that what you mean?

Carl wrote:

> Werent most if not all aircraft TX up to then just free running oscillators 
> such as the BC-191, 375, and the big Navy rigs, etc.  Even USN shipboard 
> were variable.

That's right.  The USN command sets (RU/GF, ARA/ATA, ARB/ATB, AN/ARC-5), USN
liaison sets (GO, GP, ATD), USAAF command sets (SCR-*-183/283, SCR-274-N) and
USAAF liaison sets (SCR-187/287) all were free running VFO sets (or M.O.) with
no crystal in actual frequency determining stages.  Even the ATC and
AN/ART-13* installations, which had built-in CFI systems, still retained a
BC-221-* or LM-* external CFI.  That was unnecessary, since the transmitter
could be calibrated with its internal CFI and the receiver (like a BC-348-*)
netted to the transmitter with a MONITOR-NORMAL switch (in the USAAF) or just
by keying the transmitter (in the USN).

The only crystal-controlled aircraft radios in common usage in WWII were the
VHF command sets AN/ARC-1, -3, -4, and -5, and the SCR-522-A.  No MF/HF sets
(below 20 MHz).

On the ground the situation was similar with the various MF/HF transmitters
in the SCR-177-B, SCR-188-A and SCR-193-* (BC-191-*), SCR-284-A (crystal
calibrated), SCR-288-A, and SCR-506-A (crystal calibrated).  All these were
free-running VFOs.  The first common VFO or crystal-controlled MF/HF sets
were the SCR-245-A (BC-223-*) SCR-299/399/499 (BC-610-*), and the SCR-694-*
(BC-1306-*).  The SCR-543-* (BC-669-*) is crystal controlled (no VFO) on 
transmit.

At sea, the TBX could be crystal controlled or VFO on transmit, the TCS
could be crystal controlled or VFO on both transmit and receive.  Sets
like the MO-1, MAK, MBF, and TBS were crystal-controlled on both transmit
and receive. 

VHF low-band tactical FM sets were crystal-intensive, as described below.

> The Army ground troops and mechanized used lots of crystals.

The SCR-508/528 and -608/628 are crystal controlled transmit, the SCR-509/510,
-609/610, and -619 are all crystal controlled transmit and receive.  The SCR-300-A
(BC-1000-*) is VFO only receive and transmit, but with crystal calibrator.  The
SCR-808/828-* is VFO only, receive and transmit, its four channels set through
a crystal calibrator system. (This set was intended to partially fill the role
of the ten-channel SCR-508/528, eliminating the 80 crystals required per BC-604-*
transmitter.)

Of course, there were all the crystal controlled SCR-511-* (BC-745-*), SCR-536-*
(BC-611-*), SCR-585-* (BC-721-*), MAB, and DAV portable units, all crystal
controlled for both transmit and receive.  There was also the TBY, VFO, with a
primitive crystal calibrator of sorts.

Mike / KK5F