[TowerTalk] XM240 to Moxon

[Jim Thomson]

Date: Tue, 24 Aug 2010 19:00:05 -0500
From: "Tim Duffy K3LR" <k3lr at k3lr.com>
Subject: Re: [TowerTalk] XM240 to Moxon

Hi Jerry,

Here are two mechanical designs for the 40 meter W6NL Moxon. Standard and
heavy duty.

The performance of the W6NL Moxon is very good. Good gain, good F/B and low
VSWR across the entire band - on a 22 ft boom. The Moxon's replaced
CushCraft XM240s at K3LR.

http://www.k3lr.com/engineering/moxon/W6NL_Moxon104.pdf

http://www.k3lr.com/engineering/moxon/W6NL_Mox_100.pdf

I have a pair of these two element antennas up at just about the same
heights that I have a pair of full size 4 element OWA Yagi's. 

On air comparisons show the OWA stack to have almost 7 dB more gain and 10
dB more front to back over the Moxon stack. This is what you would expect
given the element and boom size difference.

###  7 DB ?     That's a huge difference.. and then some.  What does  EZNEC
depict.    I would have thought the Moxon's would be something like 4.1 dbd...
and maybe 6 dbd  for the full size 40m yagi's.  IE:  a 2- 2.5 dbd diff  at most. 

## depicted gain from eznec/ YO  vs real life has baffled me for 38 yrs now.   I switch
from my 5-el 20m F-12  yagi..to my wire ant... and I lose 12.8 db..[using a calibrated
stepped attenuator].    The folks in EU all say I drop 6 x S units... go figure.   And the
yagi is supposed to be  7.3 dbd.   This huge discrepancy  is always  more noticable   when
pointed at EU, here from the west coast.   Everybody else here in town has noticed the same thing
at least as far back as the mid 60's.   Folks who have gone from a TA-33 jr..to a 204BA  will see
almost 10 db difference... and that switch has been done at least a doz times here in town. 

##  Does anybody else see similar effects... whereby gain differences are way nore than what
software predicts?   The diff between a rotary dipole on 80m.. and a 2-el is another one that baffles
me  [same deal on 40m].   It's like throwing a light switch. 

later... Jim   VE7RF




The Moxon pair has a little more gain as compared to the DX Engineering four
square that we use as well (expected).

A pair of two element W6NL Moxon's weighs about 100 lbs and the pair of four
element Yagi's weigh a little over 700 pounds...

73,
Tim K3LR