[ARC5] WWII Aircraft Antenna AN-104-series

[Mike Morrow]

Taigh wrote:

>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. 

Those are absolutely wonderful pictures of several different ways of mounting this mast.  Very informative...they more than fully answer my questions!  No matter how well the AN-104 works, it's apparent that proper installation required a fair amount of thought and tayloring to each type of aircraft, using structures not provided standard with the mast.

This morning I found a figure in an late revision (June 1944) of the SCR-522 manual that depicts the AN-104-A, and another that depicts the AN-104-B.  The AN-104-A is about 1 inch shorter than the -B model, and has a ground strap connecting post similar to what Jay described on the earlier AN-74.  Unlike the AN-74, the AN-104-A has a hole rather than a flange near the top of the metal mast for the forward support of an HF antenna.

Information found in several radio manuals goes on to state that the maximum length of any metalic wire going from the top to the mast to the forward HF wire antenna insulator should be no longer that 2 inches, and that no painting or caulking should be made around the bottom of the metal mast, and that the airframe surface should be no closer that 3/16th inch from the bottom of the metal mast section.

I suspect that the AN-104 has such a low and flat SWR profile across the wide frequency band of 100 to 156 mc due to the natural bandwidth broadening that results from the very large (three inches long, 1.5 inches wide at bottom) effective cross-section of the radiating mast...perhaps there's even a small "discone" effect.

The USN's later VHF rod antenna AT-8/AR would be much simpler and cheaper to manufacture and install, but it can't possibly have had the flat SWR bandwidth of these broad mast antennas.

It's funny how something as simple as a VHF mast antenna designed at least 65 years ago can still be very technically impressive.  That's what I like about this gear.

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

It was great to visit your web site again.  I had not seen that beautiful AN/APS-13, SCR-695, and SCR-522 aircraft installation before either.  Beautiful!  It's always great when someone selects an authentic aircraft to go around the radio gear.

Thanks much!

Mike / KK5F