The W6NL Moxon design uses schedule 80 PVC pipe for the driven element
insulation. F12 at one time did use ABS pipe since that was on my
EF180C. ABS drain pipe is a bad idea since the core is foamed and
compresses easily over time, so the element clamps were loose on the
EF180C.
The tolerances for the fit of the Moxon insulator are too tight at the
extremes allowed by the aluminum od and PVC pipe id specifications.
Heating the PVC in some boiling hot water solves that problem since the
PVC expansion coefficient is sufficient to increase the id enough. One
antenna we built went together easily, the other needed the PVC heated up.
Grant KZ1W
On 8/5/2014 8:36 AM, Pete Smith N4ZR wrote:
Force 12, for many years, used ordinary gray PVC tubing, split
lengthwise, to insulate its elements from the boom and any metallic
mounting hardware. The element mounts are aluminum sheet hat
sections, pop-riveted to the boom and u-bolted to the element/pvc
sandwich.
73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.
On 8/4/2014 5:42 PM, Georgens, Tom wrote:
I have built two of these antennas and I am very pleased. While I do
not have an antenna range to measure pattern, they seem to be very
solid performers. SWR is below 1.3:1 across the entire band. The
prime motivation was reducing maintenance. The 403BA needed more
maintenance interventions than the other 5 yagis combined (probably
times 2). So far so good.
One was built starting with a 402CD and the other from scratch. I
found cleaning the old aluminum tedious and probably more time
consuming that starting with new tubing. All cutting was done on a
table saw with a cheap abrasive blade and all drilling was done with
a home depot drill guide.
Since it is not a kit, some ingenuity is necessary on the element
mounting and, should you go that way, the element supports. I used
channel and the DXengineering blocks to mount the elements.
One thing you should consider is how to get the antenna on the
tower. A crane or a tram is the best bet. If you are going to twist
it through guy wires, or assemble at the top of the tower, the T-bars
make this approach very complicated. I did the twisting method and
we could not get it done without dropping a guy at each level.
Good luck
73, Tom W2SC 8P5A
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf
Of L L bahr
Sent: Sunday, August 3, 2014 1:07 PM
To: TowerTalk
Subject: [TowerTalk] Building a W6NL Moxon 40 Meter Beam.
As mentioned on another post and subject, I am going to build a 40
meter W6NL Moxon Beam. The center of the Director is split and is not
at ground potential. I see a lot of builders have used a two foot
long aluminum channel to mount the Director and Reflector to the
boom. They use a plastic or fiberglass sleeve to isolate the director
from the grounded Boom. I can see this would make for a very strong
support.
1. All this to me means, 2 foot of the radiating part of the
Director is close coupled to ground. I'd think this is Bad!! Seems
to me the use of a Delrin spacer rod or fiberglass sleeve with just
the use of U-bolts without the 2 foot of aluminum channel would
dramatically reduce the Director coupling area to the grounded
aluminum channel.
2. Also, the feed point on all the versions I have looked at couple
an RF choke right to the center point area of the Director. When I
built a couple plain Yagi antennas, I used a Gamma Match or T match
thus tapping the Director element at a 50 ohm point rather then at
say at a 15 ohm point or so right at the center of the director. Why
is this not done on the W6NL building examples? Is it because they
think and hope the RF balun choke is going to keep the mismatch SWR
in check? Can anyone explain this to me? I'm not sure, but I suspect
the impedance right at the center of the Director is not 50 ohms or
even close to being 50 ohms.
Anyway, I thought I would throw these two concerns out for you
experts to comment upon. Am I thinking clearly and correctly or am I
wrong somewhere?
Lee, w0vt
Houston
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