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[TowerTalk] Advice on 2 el 40M Vertical Array

To: <>
Subject: [TowerTalk] Advice on 2 el 40M Vertical Array
From: (David Aslin)
Date: Sat, 19 Jan 2002 16:02:30 -0800
Bud, I had a real estate-constrained location when I was in UK.  Solution
on 80m was 2 Force12 EF180BVs (37 foot tall, linear loaded) spaced 1/8
wavelength i.e. 30 feet.  Didn't have room for extensive radials.  

What I found was that laying a good number of radials between the bases of
the verticals in a diamond pattern (imagine the radials leaving the
vertical bases only in the 180 degree sector that lies in the direction of
the other vertical) gave me a 2-ele array that worked well. I did have a
ground line, bonded to the phasing box, to which I terminated the
between-the-verticals radials.  Later I added some really short radials
(varying from 10-20 feet long) in the 'outer' 180 degree sectors and
noticed some improvement in performance.  Total area occupied around 60
feet by 40 feet - so a 40 meter version would fit into the smallest of

Performance?  Consistent top 5 finishes in CQWW single band 80 and 285
countries in ca. 18 months.  (No beverages, loops etc on receive - just the
array).  Great f/b to nullout Europe on the short path to the US.  The
array wasn't great in the broadside direction, but still allowed me to work
all the countries I need off the side.  I'd guess 3-9dB down.  

A couple of details - I used the Lewallen method per ON4UN, with
guesstimates of the C and L values as I had no access to a vector analyser
or accurate noise bridge.  The MFJ 259 was unhelpful, except as rough
esimate that each vertical had a similar impedance - the measured values
did not yield the right answers for the phasing componets.  My technique
was to buid a xtal oscillator for the band, connect it to a mobile whip
antenna and park my truck about 5 wavelengths away in line with the
verticals.  Then connected a trusty IC-735  at the phasing box and tweaked
the C and L for minimum S meter reading with the array firing away from the
truck/oscillator.  A little crude, but effective. Similar should work with
the Christman method, but adjustment is tricky.  Just using ON4UN's example
lengths of coax won't cut it - the impedances in your array will inevitably
be different than his, so you'll have some cut-and-try to do.  That's why I
used the Lewallen, wth an Airdux coil/alligator clip and a couple of big
variable C's (don't forget to replace the clip with a hard-soldered
connection after setup if you pln to use power - I fried mine first time
out!  And if as I did you use receive type variable Cs, replace them with a
combination of fixed Cs to the same as the adjusted value - and use
doorknobs or similar, there's a lot of current circulating.)

Biggest losses in the array are close in to the base of the verticals - I
used 3ft x 3ft sheets of aluminum at the bases, with holes every couple of
inches around the edge through which I bolted s/s hardware with solder tags
to attach the radials.  I worked on the principle that since I could only
have short radials, I'd better have many of them - ended up with about 80
per vertical, all of 20ga wire - just kept adding them when I had spare
time in the yard.

Hope this helps


G3WGN, 80m op at M6T
From: Bud Semon N7CW <>
To: ''
Subject: [TowerTalk] Advice on 2 el 40M Vertical Array
To: <>
Date: 16 January 2002 18:17

I'm looking for a small improvement in my 40M signal and have the following

thoughts and constraints.  I'm currently using an 80/40M trapped vertical 
(similar to the BattleCreek Special, without the 160M section) over a
set of radials.   The yard is fairly small and 80M radials can only cover
90 degree quadrant.

For the moment, I will do without 80M.  I can squeeze in 2 40M verticals
1/4 wave spacing, but the radials would only cover about 270 degrees around

each vertical.  If I use 1/8 wave spacing, I can pretty much cover 360

Since I am mostly a DXer, with limited contesting and my location is in San

Diego, the most important directions for me are NE and SW, which is
for locating the verticals.  I haven't seen a way to phase 1/8 wave
for a broadside pattern, but I don't really care too much about those 
directions.  Also, being in the most southwestern corner of the country, I
no QRM from the SW when I point NE (the ocean is out there) and little QRM
the NE when I point SW (this is the LP and the sun is up to the east of
 Consequently, I think working hard for the last couple of dB of F/B is not

worth it.

So....looking through ON4UN's book, the 1/8 wave spaced array with the 
Christman coax feed method seems like a good fit.  Does anyone have a

I also have a couple of specific questions.  Are the impedance measurements
can make with the MFJ259 accurate enough for proper phasing calculations 
(including the mutual impedance)?  For radials that run between the 2 
verticals, should I terminate them in a ground line that bisects the

Thanks in advance for any thoughts and 73,  Bud  N7CW

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Where do you get ICE bandpass filters & beverage matching boxes?  The
same place that pays for the hosting of this list:  The eHam Store.
Order online at

FAQ on WWW:     
Administrative requests:

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