RCA HF Command Set Radio- Time Frame

David Stinson arc5 at IX.NETCOM.COM
Wed May 12 10:47:19 EDT 1999

Hue Miller wrote:
> --my point is that the liaison / command division arose from the
> actual installation on the aircraft and its intended role,
> not so much on the physical equipment by itself. Many (most?) of the
> classic multiseat planes of this era did not have equipment to make
> that distinction. The equipment fulfilled all roles, up to the limits
> of its abililty.
There actually was a distinct difference both in equipment
and mission in the majority of multi-seat aircraft.
"The Radio Operator's Information File," issued to the
radio op in every USAAF multi-seat aircraft, contains
distinct chapters defining distinct equipment and
distinct missions for Liaison and Command equipment.
Signal Section Air Command's
"Airborne Radio Equipment Handbook" (1943)
gives some examples and I've included some
Navy installations from other sources:

PBY          GF/RU            GO-9
 "           ATA/ARA          GO-9
PB4-Y        AN/ARC-5         SCR-287
B-17, -24,   SCR-274, -522    SCR-287
B-26, C-47   SCR-274, -522    SCR-287
B-29         SCR-274, -522    SCR-287, AN/ARC-8

There were exceptions of course- especially
after the aircraft had been "in theater" for a while.
Anti-Submarine dirigibles used TCS sets in both roles,
but they didn't venture far from shore so didn't need high power.
Many notable craft had only one or the other set.
The early Douglas A-20 medium bomber was usually issued
with only Command equipment, and the C-54 transport
with only the Liaison equipment.  The reasons?
The C-54 did not usually fly as a part of a large formation,
and the early A-20 was not designed for long-range missions.

> --your spec'd range is okay for the RU/GF. the ATB range on CW,
> with trailing aerial, would certainly be greater than this.
> ( i am guesstimating 100 miles, CW,...
I submit that 100 miles falls within my "tens of miles" range,
although 100 reliable miles is pushing it for a GF/RU, which
was not designed to use CW as a primary mode.
Liaison sets were designed for ranges up to 1000 miles or even more.

It's also important to note that Liaison sets were designed
with CW in mind.  Command Sets were designed with AM in mind.
Each could do the other's job, but much less well.
A good example is the SCR-274N (army "ARC-5) in the B-17 or B-29.
Everyone in the aircraft could talk on it using AM phone,
but only the pilot had a CW key, which was mounted on the transmitter
control box.  The radio operator could key it, but he'd
have to haywire a key to the modulator jack in the radio room
and get the pilot to switch the mode to "CW."
In the B-24 and B-25, even the radio op would have
trouble reaching the modulator, which was mounted away
from his position.
The SCR-287 is unreliable on AM above 4 MC.

Also important-  Most command sets had no provision
for "pilot" and "radio operator" control boxes, nor
have I ever seen after-market changes to provide this documented.
Control was with the pilot.  The only exceptions
I know of are the ATB/ARB and post-war installations
of AN/ARC-5 in Navy bombers.

> A book I have ( maybe "Your Flying Navy" ?? ) seems to state that
> the ATB, as used on Kingfisher, was installed here specifically as
> a longer range radio - a role here, for example, comprising both
> 'liaison' and 'command' roles.
The Kingfisher and other such scouts weren't designed
to stray far from their bases, so didn't need high radio power.
"Longer range" in this context is the difference between the typical
20-30 miles of a GF/RU vs. the 50-70 miles of and ATB/ARB.
According to the ATB manual, the power actually delivered
to an aircraft's very short, fixed antenna was around 2.8 watts.
So the ATB could not be expected to perform over the 500-1000 mile
distances for which Liaison sets were designed.
This might be overcome to a degree with the use of a trailing wire,
such as surely was done in the case of the Kingfisher.
But even with full CW output going to this antenna,
we're still talking about 20 watts.  Liaison sets typically
output 75-100 watts to a resonant, full-size trailing wire.
Moreover, in many years of reading the literature
I've never seen a command radio,
when specifically installed as a command radio,
connected to a trailing antenna.
I'm sure there are exceptions; I've just never seen any.
In cases where Liaison sets were not installed or were inoperative,
command radios were often used as "auxiliary liaison"
by haywiring them to a trailing antenna and
with the understanding of the limited range this afforded
relative to a full-size Liaison set.

>.... both pilot and radio operator could operate the radio,
>altho only the radio operator actually had a key,
>and access to the tuning controls.
This is a very notable exception specific to the Navy
light patrol and torpedo bombers like the TBM.
The later TBMs typically used the ART-13/ARB in both
the command and liaison roles.
An ARC-5 R-23 was also installed for radio range use
and an ARR-2 for homing/navigation back to base or carrier.

73 OM DE Dave AB5S

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