[Top] [All Lists]

[TowerTalk] Modified Cushcraft 40-2CD

To: <>
Subject: [TowerTalk] Modified Cushcraft 40-2CD
From: (
Date: Wed, 12 Mar 1997 15:03:57 -0500 (EST)
In the "for what it's worth" catagory...

I have build two (2) Cuscraft 40-2CD yagis, new out-of-the-box with the
structural improvements suggested by Dave Lesson following BOTH the QST and
the NCJ articles. (There is valuable information in all of them.) One of
these withstood two successive huricanes that hit the island of Montserrat a
couple of years ago. In my opinion there is no better 40 M yagi available for
the price than the 40-2CD with the "QHS improvements", both performance wise
and structurally.

A couple of additional comments. I went to the trouble of obtaining two 8"
lengths of nominal 2" dia. high density polyethylene round stock, and having
them milled to slip into the ends of the boom. This eliminates the
deformation of the boom as the element-to-boom u-bolts are tightened. (A
simpler, cheaper approach is to get PCV tubing and saw a longitudinal slit so
the section will fit into the boom ends.)

A more important improvement involves the loading coils. The OD of the
fiberglass (?) rod upon which the loading coil is wound is quite a bit less
than the ID of the aluminum tubing into which it fits. As time passes and the
effects of wind and temperature do their thing, the loading coil will tend to
"wobble", and will work it's way loose until it is visibly
out-of-alignment... possibly opening the coil/element connection. The simple
expedient of adding a thin sleeve of shim material to the OD of the coil rod
so it is a tight fit in the element will prevent this from happening. I also
use stainless steel sheet metal screws to secure these joints along with the
compression clamps provided.

The next step is to carefully cut away the black insulating material from
over the screws that connect the ends of the loading coil wire. I use an
Exacto knife to scribe a small cirrcular section around the screw heads thus
not disturbing the remaining insulation. Then replace the "factory" screws
with stainless steel sheet metal screws. (I also use Penetrox on the
contact.) Otherwise corrosion will eventually build up around the
screws/wire, and lead to erratic contact. Seal the cut-away section with RTV
or equivalent. Also run a bead of sealent around the junction between the
insulation ends and the element. 

I'm sure others have solved these same problems in other ways, but it's
worked for me, and it's so easy to do at the time of initial assembly. 

Hope this helps someone avoid some very pesky problems. I'd put together
several 40-2CDs prior to this... they played very well... for a while... and
then... ooops! Some years ago I put up one at ZF8AA's place on Little Cayman
(abouit 30 yards from the beach). It played like a "hose" for the first year
or so, and then became trash!


Joe, W5ASP

FAQ on WWW:     
Administrative requests:
Sponsored by:             Akorn Access, Inc. & N4VJ / K4AAA

<Prev in Thread] Current Thread [Next in Thread>