[ARC5] Command Set Loop Connections

[Mike Morrow]

>> Yes, this is an interesting "one".  I don't know these sets well
>> enough to know if the broadcast band sets came with a "loop" antenna
>> selector.
>
>Some did as far as I know. The receivers up through the 1.5 to 3.0 Mhz 
>version were known as the Navigation Sets....at least according to my ARC-5 
>manual.

The only "command set" family receivers that had loop connections were:

RAT:          NONE
RAV:          CBY-46102 (.19 to .55)  CBY-46103 (.52 to 1.5)
ARA:          NONE
SCR-274-N:    NONE
AN/ARC-5:     R-23, R-23A, R-148 (.19 to .55)   R-24 (.52 to 1.5)
ARC Type 12:  R-10A (.52 to 1.5)     R-11A (.19 to .55)
              (These Type 12 sets had BNC loop coax connectors.)

The AN/ARC-5 receivers that covered above 1.5 MC were communications sets,
without loop connection.  All AN/ARC-5 comm sets except early ones were
stabilized.  All AN/ARC-5 nav sets had loop connections.

>>  I have a "navigation band" set (late WWII) with a "loop"
>> antenna selector.  The setup is identical to what I see in the photo. 
>> This is consistent with your observation about stencil showing 190 to
>> 520kHz on the back panel.
>> 
>> Since all the IF transformers and the coil pack mount in sockets in,
>> it's would be easy to believe these sets were made in a basic
>> configuration (valves, tuning capacitor, wiring) and "configured" by
>> simply by plugging in the correct coil box and IF transformers.  At
>> least this is how I imagined the design concept at first.  I was
>> always impressed by this concept.  Very clever.  Wrong, wrong, wrong,
>> or at least not that simple.  Different sets in the same series (eg
>> R-23 and R-26 from the ARA specification) have small components that
>> are different.   For example, the local and BFO plate dropping
>> resistors are not the same value across the range.  The lower
>> frequency sets use higher value dropping resistors than the higher
>> frequency sets.

The CBY-46129 and CBY-46105 were the ARA equivalents to the R-23 and
R-26/ARC-5.  There's not much difference between any of the ARA sets.
The AN/ARC-5 sets are a different story.

The R-23, -23A, -148, and -24/ARC-5 "navigation" sets have a special audio
output off the cathode circuit of the 12A6 that is goes to the connector
for the front panel adapter.  This was intended to communicate receiver
audio to the MX-19/ARC-5 audio adapter panel interface to the AN/ARN-9
"Air-Track" ILS.  The receiver would be tuned to the appropriate frequency
of a LF/MF localizer transmitter for this early ILS.

The Air-Track ILS died a well-deserved death before WWII ended, a victim
of the gross superiority of the USAAF's SCS-51 ILS (which included a VHF
localizer receiver (RC-103-A) and a UHF glide slope receiver (AN/ARN-5)).

I doubt that the AN/ARC-5 loop connections were ever used in a military
environment.  DU and DW loops were pretty outdated by WWII, especially
with the arrival of the USN's ZB (and AN/ARR-1 and AN/ARR-2) VHF homing
system.

>Yes. And according to the ARC-5 manual I have here (I'll have to check the 
>number and post here) there were other differences as well. AGC circuitry 
>was different. Stability of the HF oscillator was changed in some of the later 
>AN/ARC-5 models to enhance it, etc. Those higher-stability units, also known 
>as "lock-tuned" (I think), had a yellow letter "S" inside a yellow circle stamped 
>on the front panel.
>
>>  I assume this is because the oscillators "take off"
>> more readily at the lower frequency.

WIth respect to the oscillators, that is NOT the explaination for the nav sets
not needing special stabilization.  Stabilization is of little value if the
receiver will not be fix-tuned.  Nav sets could never perform their function
if fix-tuned, no matter how stable they were.

The R-25, -26, and -27/ARC-5 communications receivers were stabilized for 
lock-tuned service so that they could be set to the frequency of the 
associated transmitter.  No tuning spline and panel was attached when they
were employed in fix-tuned service.  (But sometimes the comms set were remote-
tuned.)  This eliminated the troublesome "coffee grinder" controls of earlier
models.  Keeping a communications receiver tuned to the frequency of the associated
transmitter must have been quite challenging with those command sets that
had easily disturbed grinder cranks instead of the AN/ARC-5 fix-tuned receivers.
There is NO way to net a receiver to the associated transmitter using a
MONITOR-NORMAL switch such as is found in the USAAF's SCR-287 and AN/ARC-8.
When a command set transmitter is keyed, the audio heard in the headset is
the 1000 cps tone generated by the modulator, not the audio output from a
receiver.  The receiver can not be tuned by the pilot in search of his
transmitter's output.

The use of the navigation receivers was a completely different story.
Stabilizing a beacon band R-23/ARC-5 would be pointless, because it would
always need to have pilot-controlled remote tuning so that the various
beacons and LF/MF control tower frequencies could be selected during flight.
The R-23 with MX-19/ARC-5 audio adapter was also intended to be used as
localizer for the AN/ARN-9 ILS, which would require tuning to the appropriate
frequency at each ILS installation.

Likewise, the R-24/ARC-5 with MX-20/ARC-5 power adapter by was intended only
for use with the AN/ARR-1 (or ZB) homing adapter.  It would need to
be remote-tuned in flight for the various BCB modulating frequencies of the
AN/ARR-1.  So...stabilizing an R-24 would have been pointless.

Unfortunately for the R-24, the development of the AN/ARR-2 homing receiver
(which completely replaced the R-24/ARC-5 with R-1/ARR-1 homing adapter),
eliminated its primary homing function.  That's why surviving un-ham-hacked
R-24 sets are invariably in never-used-by-the-military condition.

The post-war ARC Type 12 nav receiver systems did return to the use of manually
directed loops usable in the .19 to 1.5 MC region, as was common with many
other civil aviation sets of that era.

Mike / KK5F