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Re: [TowerTalk] Moxon questions

Subject: Re: [TowerTalk] Moxon questions
From: "" <>
Date: Thu, 16 Dec 2010 10:35:28 -0800
List-post: <">>
Funny timing.

I've been playing with a M2 40M 2L conversion. last year I had expanded it to a 
full size 2L with bent tips vertically, but just 
changed that last weekend to a Moxon. Still testing things. SWR/bandwidth looks 
great. I originally wanted tubing on the sides, 
but had too much droop and switched to wire. Then, playing with 4nec2x, I 
decided that droop was not a bad thing. I just modelled 
the droop as an optimizing variable, along with the wire lengths. The boom is 
about 19-1/2', I added about 40" tubing to each 
element half over a stock 40M2L. Wire droop on the sides can be 2'-4'..tip 
spacing about 16". Taller center truss support. two 
truss lines out to the longer elements on each side.

With droop, there is less horizontal pull on the elements, so less deflection. 
I used a wire sag calculator to figure out what 
amount of droop gave a reasonably minimal side pull. (for the weight wire). The 
current is low at the ends, which so using wire 
isn't bad.

It's an interesting 3D question. W6NL has shown you can play with 
loading/coupling. By allowing droop, you can have different 
interactions of gap, wire length, boom length. No one legislated that 
everything has to be inline.

I had already bent 90 degree tubing angles for the ends, so my wire is attached 
to the aluminum tubing elements without bending 
it. (it attaches to the arm of the bent tubing with hose clamps). I twisted the 
90 angle so it points inline with the drooping 
wire. So it's a straight line for the wire. Bending 6061 tubing takes some 
attention/technique but I got good results.

I was going to use some 12 gauge aluminum wire, but right now it's just 12 awg 
thnn copper, with the ends tinned where they clamp 
to the aluminum.

I found with modelling things, that there is a lot of flexibility in terms of 
what dimensions give the desired SWR/bandwidth/gain.

In terms of model vs real life, I found that my model seems to be higher in 
freq than real life, so I optimized for 6.9Mhz and 
things seemed about right. The swr curve not symmetric either, so it pays to 
optimize low. I had noticed when trying to sim the 
W6NL moxon conversion, that it seemed to center lower for me too, so I just 
assumed something must be consistently off.

I don't have much wind and not much time in the air with this yet, but that's 
what I've got.

When I had the 19-1/2' boom as a yagi with bent tip elements, I used a copper 
tubing coil as a hairpin. Found I couldn't get 
enough inductance out of a normal hairpin design to get a match. 



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