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[TowerTalk] Feedline choke for A3 beam

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Subject: [TowerTalk] Feedline choke for A3 beam
From: (Bill Coleman AA4LR)
Date: Fri, 26 Sep 97 17:25:24 -0400
On 9/25/97 11:29, yo3ctk at wrote:

>In the (very short) Cushcraft A3 installation manual it is written that
>one should make a choke balun by coiling the feedline (8 turns, 6?
>O.D.). and then: ?tape the coiled feed line choke to the boom near the
>feedpoint?. I am worried that this coil would be too heavy and will
>unbalance the antenna, not to mention that it will add to the wind load.

Nah, it isn't that heavy, and doesn't add appreciably to the wind load.

When I had my A3 up, I taped the coil to in the "corner" between the boom and 
the mast. It stayed up there over six years, and I didn't even use quality 
tape. (like Scotch 33)

>Moreover, placing the coil in the immediate vicinity of a metallic
>object (the boom) will upset the performance of the balun.

No, the presence of nearby metal won't affect it overly much. The idea is to 
prevent currents from flowing on the outside of the coax.

> So my
>question is: this coil is to be hanged from the boom or attached to the
>mast ? And using tape to fasten such a heavy object, which will surely
>swing in the wind, is really a reliable method ?

Worked for me.

> Finally, how long
>should be the ?free? portion of the cable, between this damned coil and
>the first attachment point to the tower (allowing the antenna to rotate)
>? (OK, so there were three questions :-))

Well, I taped mine up against the mast, and taped it down lower on the mast 
every 2 feet or so. When I got a foot above the top of the roof tower, I taped 
it to the mast, then left lots of slack and taped it to the tower. This formed 
a "loop" that allowed the rotator to turn.

The alternative to using the coil balun is to use one of the commercially 
available bead baluns. (W4AN suggested this some time ago) This has the 
advantage of supplying an SO-239 connector to plug the coax into, so you don't 
have to try an weatherproof the split coax at the antenna. Instead you 
weatherproof a PL-259 connection, something that has been discussed at length 
on TowerTalk.

Another alternative is to use a set of several ferrite beads designed for coax 
cable, in essense creating your own bead balun. 

Any of these alternatives should work equally well.

Bill Coleman, AA4LR, PP-ASEL        Mail:
Quote: "Not in a thousand years will man ever fly!"
            -- Wilbur Wright, 1901

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