[ARC5] Command antennas

[Mike Hanz]

The antennas that KK5F outlined below are fairly typical of the last 
generation of HF aircraft antennas during the war.  There was also a 
curious so-called "shunt fed" antenna that was used for a time on the 
B-17s and early B-29s, perhaps a few others.  It was basically a short 
wire from just above the radio compartment down to the cowling on the 
number three engine, the complete circuit then returning to the 
transmitter through the wing and airframe to the ground terminal on the 
transmitter.  I've never found any performance figures on it...for a 
short range command set it might have been entirely satisfactory.  Its 
greatest drawback was the transverse position of the wire, which cause a 
lot of "thrumming" by the wind, and they were reportedly much more 
vulnerable to bird strikes and the occasional line maintenance guy 
working on the engine.  With the real estate available on the larger 
aircraft, it was just as easy to run a second "long wire" antenna to the 
tail, and eventually I think all the USAAF and Navy aircraft ended up 
with that kind of configuration by the end of the war.

I won't belabor the excellent work of KK5F, AB5S, and a number of others 
on this list of others in describing the compromises necessary to run an 
aircraft set with a typical ham antenna, but the simple answer is that 
the transmitters are designed to "see" the characteristic impedance of 
an aircraft antenna at their output terminal, so whatever matching is 
necessary to create that condition is what works best.  I have an 
article posted on the docs page that describes the graphic calculation 
of driving point impedance for a number of aircraft configurations, as 
well as some information on typical long wire impedance variations with 
frequency - http://aafradio.org/docs/Aircraft_Antenna_Design.html is the 
link.  If you're into authenticity, a 75 foot long wire antenna in your 
back yard, with a single wire counterpoise in the grass, will 
approximate the impedance plot over the HF range of an aircraft antenna 
on a large plane. :-)

73,
Mike  KC4TOS

On 8/11/2012 12:33 AM, Mike Morrow wrote:
> Mark wrote:
>
>> What type of antenna did the command sets use in B-17 and B-24 bombers?
>> Did they use the same antenna (trailing I presume) as the liason sets?
> The MF/HF command set and liaison set used different fixed wire antennas
> running from the middle to forward section of the fuselage to the tip of
> the rear stabilizers.  Additionally, the liaison set could be connected
> to a retractable trailing wire antenna up to (typically) 250 feet long.
>
> Take a look at Mike Hanz's web pages at http://aafradio.org .  The following
> pages have excellent depiction of B-29 external antennas.  The liaison and
> command MF/HF antennas of the B-29 are similar to the installations typical
> of most WWII USAAF bombers.
>
>     http://aafradio.org/NASM/RHAntennas.htm
>
>     http://aafradio.org/NASM/LHAntennas.htm
>
> See also these B-24 diagrams from VE3FAB pages at http://jproc.ca/ve3fab/b24.html :
>
>     http://jproc.ca/ve3fab/liason.jpg
>
>     http://jproc.ca/ve3fab/cmdsys.jpg
>
> The last two diagrams come from the "Radio" volume of Consolidated's
> seven volume 1942 Service and Training Manual for the B-24D.
>
> Mike / KK5F
>
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