The WW-II Era RCA Light Aircraft Radios

[David Stinson]

(I've also collected these for a long time)
(Posted to the list for general information)
-----------------------------------------------
Introduction to WW-II Era
RCA AVT and AVR Series Light Aircraft Radios.

The RCA AVT/AVR series of radios were introduced in the mid-30s
for use in light civilian aircraft. Many models of the line were
pressed into service early in the war and officially adopted later.
Most served in either light spotter aircraft, such as the
Stinson L-5, Tailorcraft L-2, and Piper Cup, or as "ferry" radios.
They were all very small, light weight, extremely
simple in design, easily produced, and very effective.

"Ferry Radios"
Military aircraft built in the U.S. were "ferried" to their
units before final outfitting. Ferry pilots used the "radio range"
system while crossing the U.S. and most allied countries,
and needed a means of plane-to-plane and
plane-to-tower communications.

The Radio Range system used navigation beacons in the 200-400 KC
range and a "standard" tower-to-aircraft frequency of 278 KC.
Aircraft-to-tower transmissions were usually on 3105 or 6210 KC.
Also, the ferry pilots needed a "standard" radio channel
for plane-to-plane work-- usually also on 3105 KC.

U.S. Army Air Corps units in different locations tended to use
different types of equipment and/or frequencies.
A P-47 for instance, delivered with an SCR-522 in it would have
to sit on the ground for refit if that squadron
was using the SCR-274. Better to deliver the aircraft sans radios
and let the ground crews install the proper set in-theater.

To solve these problems light, easily-removed radios were
tacked into the aircraft before it's delivery flight.
Once the aircraft was delivered, the "ferry" radios were removed
for the trip back to the factory and re-used on the next flight.
The "tack in" method was often very primitive, and could be
as simple as bolting the radios to a plywood board which was
aid on the floor of the aircraft.  Sometimes it was strapped
under the dash. The practice of "re-use" over and over again might
explain the rough condition of most surviving examples.

Light-weight, low power radios were also required in unarmed
spotter and light transport aircraft. These aircraft could overfly a
section of the battlefield and direct or correct artillery fire,
air strikes or give "early warning" of advancing enemy units.
They were usually fabric covered and capable of low passes with
high maneuverability at slow speeds. General Patton's personal
light transport aircraft was outfitted with a set of these RCA radios.

These extremely light aircraft usually lacked an electrical
system of their own. Providing power to ancillary equipment like
radios could be a problem. This was often solved by useing a
wind generator that was mounted on the underbelly of the aircraft.
It could provide power directly to the radios, or charge a battery
that fed a vibrator power supply.  Often the pilots simply
carried several fully-charged batteries along.

I don't have a complete list of RCA AVT/AVR sets that then existed
but I can discuss these following which are in my collection.
The list might serve as a starting point from which
we might build a more thorough accounting.

Receivers:
AVR-7 (uncommon).
A real 1930s multi-band "Rube Goldberg" radio.
A flat panel about 5" x 7" inches with the controls and tuning scales
mounted in the cockpit.  It was connected via spline shafts and cables
to a black box bolted somewhere on the firewall.
The band-change control is a "push-pull" cable gadget from the
panel to the electronics package,
just like an old automobile "choke"control.
Appears in a 1936 book on aircraft radio.
Military use (pre-war?) documented by a yellow
Signal Corps inspection stamp on the example in my collection.

AVR-15  (uncommon).
This radio looks just like the more commonly seen HF model AVR-20,
except that it's a "radio range" receiver tuning 200-400 KC. It has a
fixed-tune position for 278 KC, which was the most common "tower to
aircraft" frequency in the 30s-40s.
Documented military use TO 08-45-17 dated July 1944.

AVR-20 (common).
Most commonly seen AVR receiver. Mounted under the panel or on the
ceiling. 2700-6700 KC in a single band. 1930s-40s civilian aircraft
usually talked to the "tower" on either 3105 or 6210 KC and the tower
responded on 278 KC. These receivers allowed aircraft-to-aircraft
communications.  A surprisingly good-soundng receiver once recapped.
Military use documented in spotter aircraft
in North Africa 1943 (photographic), D-Day (photographic),
in military manual TO 16-45-15 July 1944, and
in the Stinson L-5 maintenance manual.

AVR-100 (uncommon).
A "mount in the panel" radio similar to the BC-1206, but
even smaller then that radio. This receiver had two bands-
BCB and BEACON (radio range), plus a fixed-tuned position for 278 KC.
Military use documented by Signal Corps inspection stamps and
inclusion of spare parts in Signal Corps SIG-5 parts catalog 1945.

AVR-101 (uncommon).
Also a very small "mount in the panel" radio, this set tuned the beacon
band 200-400 KC. Military use documented by Signal Corps inspection
stamps and inclusion of spare parts
in Signal Corps SIG-5 parts catalog 1945.

AVR-103 (uncommon).
Single band "radio range" receiver, 200-400 KC. Mounted "under the dash"
with an odd, tilted front to the chassis that displayed the slide rule
tuning dial to the pilot. Much larger then the 100/101.
I have found no evidence of military use.

AVR-104 (scarcity unknown).
A post-war set (1957).  Two parts with a control head/RF amplifier
unit that mounted in the panel and a cylindrical IF/AF electronics
package mounting elsewhere using shock mounts. Interconnecting cable.
200-415 KC with a fixed-tuned position for 278 KC.
Navy use documented by NAVAER 16-45-622.

Transmitters:

AVT-15 (uncommon).
"Big Brother" to the better known AVT-112, but only physically.
The AVT-112 is a much better design, but this one "looks" better.
Internal vibrator power supply. 2500-6700 KC two channel
crystal control.  Crystals can be changed by unsnapping
the lid on the top of the transmitter. 6L6 oscillator modulated
by a single 6L6 provided about 7 watts out.
Tunable from the front panel with a built-in RF meter.
Most often used with the AVR-20 receiver.
Military used documented by Signal Corps inspection
stamp and in the Stinson L-5 manual.

AVT-111 (very uncommon).
Same size as the AVT-112 but stripped-down.
Permanently installed crystal at 3105 KC which could be
doubled to 6210 KC. No tuning controls available to the pilot
as all tuning was done through capped access holes
through the front panel. Only controls on the front are for on/off
and switching between a trailing antenna for 3105 KC,
fixed antenna for 3105 KC and a trailing antenna for 6210 KC.
This lack of tuning flexibility doubtless caused
very limited range and may be the reason this cheaper radio
wasn't produced in the numbers of the tunable transmitters.
I haven't found any documented military use.

AVT-112 (common)
Very well designed and compact transmitter. Crystal control with xtal
socket on the front panel.  2500-6500 KC at 6 watts out. Fully tunable
from the front panel. 6V6 oscillator, 6V6 power amp modulated by
push-pull 6V6s. Dual scale tuning eye tube displays both power out and
plate current. Despite it's excellent service, they did have a problem
with breaking off the bakelite "tabs" used to slide the antenna tuning
core. Excellent audio out of this rig, even with a carbon mike. It and
the AVR-20 are both a bear to recap!  Note that most RX/TX switching in
this set takes place in the AVA-126 vibrator power supply pack.
Military used documented in North Africa 1943 (photographic), D-Day
(photographic), in a military manual TO 16-45-15 July 1944 and in the
Stinson L-5 maint. manual.

Typical Accessories:
AVR-15:  AVA-51 storage battery box.
AVT-15:  MI-5883A remote control panel (Unobtainium).
         (On/off, mike input, channel select)
In installations using AVT-15/-112 and AVR-15/-20:
        AVA-126 power supply (uncommon).
        AVA-120 Trailing antenna reel (VERY scarce).
        Crystal rack holding 12 crystals and with
        a canvas cover (rumor of one surviving).

There have been some reports of the AVT-112/AVR-20 set using storage
batteries without the AVA-126, but this is unlikely since most
of the PTT switching for this set is located in the AVA-126.
It is much more likely that these reports concern
the AVT-15/AVR-20 sets, since the transmitter's vibrator supply
was internal and the receiver could be powered from the transmitter.
This set could operate from a single 6 or 12 volt storage battery.

73 DE Dave Stinson  AB5S
<arc5 at ix.netcom.com>

*****
editorial comment)
Dave's classification of "common" is in comparison with other
radios of this same series and may not necessarily reflect
your ability to find one of these radios.

Two ground versions of these radios are known to have been
produced. Both were the result of the re-packaging of the basic
AVR-20 receiver, combined with AVT-112 into a common single cabinet.
The transmitter was modified for Master Oscillator
frequency control rather than the typical crystal control
and provisions for CW were added to the transmitter and receiver.
The resultant radio was the SCR-288(BC-474).
The second version is believed to be a very early BC-474
which included the transmitter and receiver in separate cabinets
vice a single/common one.
Only one surviving example has ever been reported and
the details on it are very sketchy.

...although these aircraftradios saw extensive military/combat use,
none were ever affixed or assigned official military nomenclature...

Dennis
****

(This piece first published on the Military Radio Group 25 Mar. 99 post.
Editorial contributions by Dennis Starks gratefully acknowledged.)

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