[TowerTalk] Building a W6NL Moxon 40 Meter Beam.

[Georgens, Tom]

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 at 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
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk