[ARC5] Antennas

[Mike Morrow]

Dave wrote:

>The AN-104 was indeed a VHF antenna.

And, as Mike Hanz points out, it has amazingly flat VSWR.  The broad
metal sheath is the radiating element, and must not be grounded to
the airframe.  I once owned a batch of four AN-104-B (all contract
367-DAY-44) antennas, one of which I attached to a large file cabinet
(as ground place).  My antenna analyzer showed a VSWR no higher than
1.3 from 100 to 156 MHz, IIRC. 

>I have seen a couple of examples with an eyelit at the tip so it
>could also be used as a mast for an HF or Range antenna.

All four of the AN-104-B that I owned had that eyelet, so it appears
these at least were manufactured that way and were not an ad hoc
modification.

>I came across this site concerning aircraft wrecks and their missing
>crews, which has significant contributions by our own Taigh Ramey:
>
>http://www.missingaircrew.com/trip/american2/
>
>Reference the Hellcat at the N.A.S.M. in Washington-
>While the radio-related photos can't be enlarged, you can see the AN-104
>just behind the cockpit, followed by what I'm pretty sure is the ARR-2
>antenna...

The AN/ARR-2 antenna would be the AT-5/AR.  I don't think that's what is
on the pictured aircraft.  The AT-5/AR (246 MHz) is a thin uncapped rod
only 11.5 inches long.  The one in the picture appears considerably longer.
I don't know what it could be except perhaps an antenna for the ABK or
AN/APX-2 IFF (190 MHz).  But it appears a little too long even for IFF.

There was a VHF comm antenna that competed with the AN-104-* called the
AT-8/AR that was just a rod antenna several inches longer than the AT-5/AR.
It wouldn't make sense to have both an AN-104-* and an AT-8/AR installed.
I've also never ever actually come across an AT-8/AR after 20 years searching.
That makes me think that it was not widely used.  Lacking the broad, thick
radiating surface of the AN-104-*, it must have had a much narrower natural
bandwidth.

>The empty ARC-5 rack has some covered connectors in front of it, which gives
>this away as a VHF/MF/ARR-2 installation from the last year of the war or
>post-war.

That in some AN/ARC-5 manuals is called the "single-seat fighter" installation,
shown on sheet 5 of Fig. 8-55 in AN 16-30ARC5-2.  That's the way I've configured
my own AN/ARC-5 set.  The receivers in my rack are R-4A/ARR-2, R-26/ARC-5, and
R-28/ARC-5.  The transmitters in my rack are T-20/ARC-5 and T-23/ARC-5.  This one
set contains an example of each of the major types of receivers and transmitters
used in the AN/ARC-5 with AN/ARR-2 system.  It provides six channels of VHF ZB
homing, one channel of HF comms, and four channels of VHF comms.  Not too bad
for such a small package (67 years ago).

>An interesting detail, concerning the need to "use what you have" even when it's
>not "by the book:"  the installation includes juntion box designed for SCR-522.

It reminds me of a picture I have somewhere of a post-WWII USN trainer aircraft.
It used two pilot-tuned receivers (R-23 for range and ground-to-air comms, plus
an R-26 for air-to-air comms) and one transmitter (T-19 for air-to-ground and
air-to-air comms).  There was *no* transmitter control box for the single
transmitter, since there was no need to select multiple transmitters or change
mode of emission.  All completely Kosher, except that the antenna switch was a
BC-442-A rather than the "proper" RE-2/ARC-5.  The photo was from the flight
manual for the aircraft.

Mike / KK5F