[TowerTalk] TELREX 40M346 (copy) PROJECT (LONG)

[Brad Anbro]

A few years ago, I helped a local DX'er friend take down his Telrex
40M346, prior to his moving out west in retirement. After we had the
antenna on the ground, I made rough drawings of the different aspects
of the construction of the antenna and measured & noted every dimen-
sion that I possibly could, in hopes of some day building a copy of
this antenna.

I have finally got around to getting the project well under way. I
used 3-1/2" OD x 1/4" wall aluminum tubing for the 22' long middle
piece the boom and 3" OD x .125" wall aluminum tubing for the 12' 6"
and 14' 6" boom extension pieces. The 3" OD tubing wouldn't fit into
the 3" ID of the middle piece, so I had to use a cylinder hone and
remove enough material for a close fit. I believe that Telrex used
3" OD x .090" wall tubing for their extensions but I wanted to go a
little heavier, as I had planned on putting this antenna on top of
a 136' tower.

For the element insulating tubes, where the elements pass thru the
center of the boom, I used 2" OD x 1/4" wall G10 fiberglass epoxy
tubing, which I had to bore out a little, as the 1-1/2" OD elements
wouldn't fit into these without some clearance. Also, I was unable
to locate the proper size of aluminum tubing for use as "protective
sleeves," to protect the insulating tubes from being worn by the
boom, where they pass thru it. I believe that Telrex used tubing on the 
order of .075" wall thickness for this. I finally settled on
using material that was salvaged from a used air-operated hydraulic
cylinder, which I was fortunate to find lying around where I work.
The "protective sleeves" wound up having a .125" wall thickness and
I had to machine the hole sizes in the boom pieces and the boom
"collars" accordingly.

Telrex originally used 1/4" dia. bolts which passed thru the center
of the insulators, to hold the elements in place. I decided to use
5/16" bolts, instead. Also, for the reflector and the director, 1/4"
bolts pass completely thru the collars and the boom to help keep the
elements from rotating. In addition to this, there are two additional
bolts, lockwashers & nuts which pass thru each collar into the boom.
These are also 1/4" dia. in size.

I am having a problem figuring out how to terminate the 1/8" dia.
stainless steel feed wire stubs on the reflector and the director;
and also the feed wires for the driven element. With the factory-
built antenna, Telrex used 7/8" OD tubing which passed thru the boom
and 3/4" OD tubing fit inside of these. The ends of the 3/4" OD
tubing were swaged flat, where the wires were fastened. One could
get the same effect by putting the piece of tubing in the jaws of a
vise and squeezing the tubing together, but my guess is that Telrex
used a stamping press and some custom-made die blocks to swage the
tubing ends. Of course, the Telrex-swaged ends looked very nice and
I am hoping to come up with something to the same effect.

Does anyone know of a machine shop that is set up to swage aluminum
tubing? These pieces are only about 8" long and 3/4" OD x .058"
wall. If I could find someone who could swage these for a half-way
reasonable price, I'd much rather have that (than sticking them in
a vise and "swaging" them that way). If anyone knows of a shop which
is set up to do this type of work, I'd sure appreciate knowing about
it. Thank you very much for taking the time to read this.

73 de Brad, N9EN

<N9EN@HOTMAIL.COM>
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