[ARC5] WWII Aircraft Antenna AN-104-series

[Taigh Ramey]

Great thread on the AN-104! It is the little things that get me all
giddy...I think I need to see a doctor...

I posted a few shots on a web page showing the AN-104 installation in a
P-47D, P-51D and a Beech 3NM. I hope this helps to answer some of your
questions about the mounting. I have also seen a block type of mount used
with stiffeners added to the structure. I will try and find a shot of that
as well.

The metal of the AN-104 was mounted above the skin as you suggested and I
have seen special molded rubber seals around it to keep the water out. I
have also seen a Permatex type of sealant used.

Try this:  http://www.twinbeech.com/radio.htm

Thanks,
Taigh
 
Taigh Ramey
Proprietor, Vintage Aircraft
7432 C.E.Dixon Street
Stockton, California 95206
(209) 982-0273
(209) 982-4832 Fax
www.twinbeech.com
KEEP 'EM FLYING...FOR HISTORY!
 

-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of Mike Morrow
Sent: Tuesday, January 02, 2007 4:16 PM
To: milsurplus at mailman.qth.net; arc5 at mailman.qth.net
Subject: [ARC5] WWII Aircraft Antenna AN-104-series

I have a couple of AN-104-B VHF aircraft antenna masts.  The AN-104 is
designed for 100 to 156 MHz, and also contains an anchoring hole for an HF
wire antenna support.  It thus serves as the VHF antenna and the forward
support for an HF antenna.

According to VHF AN/ARC-5 and SCR-522 manuals that I have:

AN-104-A    -  Used by USAAF
AN-104-AX  -  Used by USN

I have no information how these two versions differ from each other.  I also
have no details of the improvements for the AN-104-B version.  Apparently
the AN-104-series is the most common US VHF aircraft mast of WWII. 

The upper 30 inches or so of the AN-104-B is an oval cross-section *steel*
mast, wrapped around a wooden bottom section perhaps about seven inches long
that has a SO-239 connector at the bottom.  I'm having a hard time
understanding how such a structure was actually anchored on the aircraft.
Apparently the bottom wooden section would fit into some type of matching
oval socket.  The bottom of steel mast would have to be maintained somewhat
above the skin of the aircraft, otherwise the metal antenna surface would
short to the airframe.

I jury-rigged a mast to a metal file cabinet and ran a MFJ antenna analyzer
across its design range.  Very surprisingly, SWR from about 105 to 160 MHz
was below 2.5 across the range, and typically less than 1.5 from about 110
to 155 MHz.  Above and below these ranges, SWR increased rapidly.  It
surprises me greatly that the SWR of such a simple antenna mast would be so
low and flat over such a wide range.  Is there something special about the
electrical design of this mast?

The SCR-522 manual briefly mentions a proposed variable-length VHF antenna
whose length would be preset and selected through the small connector found
on the BC-602-A (but not -B) SCR-522 control box.  With the flat SWR of the
AN-104, it becomes clear why a variable-length model was never required.

I've been searching without sucess for years for an AT-8/AR late-WWII
rod-type VHF antenna, apparently used mostly by the USN.  I can't imagine
any way that a simple metal rod could show as flat a SWR over the 100 to 156
MHz range of WWII-era VHF sets.  For that matter, I'm having a hard time
imagining how the AN-104 performs as well as it does too.

Mike / KK5F
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