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Re: [TowerTalk] 80 M 4 SQUARE MODELING

To: <TOWERTALK@contesting.com>
Subject: Re: [TowerTalk] 80 M 4 SQUARE MODELING
From: "Paul Christensen" <w9ac@arrl.net>
Date: Sat, 22 Jul 2017 09:25:44 -0400
List-post: <mailto:towertalk@contesting.com>
N4CC and I will soon be grappling with the same issue at our remote Internet 
site.  We recently purchased the DXE-4SQ 80m package with Phillystran support 
cabling.  The 4SQ will surround a 100 ft. self supporting tower with a 30m-10m 
LPDA at the top.  I've reviewed several articles on de-tuning of incidental 
radiators, but would like to see some practical examples, especially where 
adjustments can be made at ground level.  Although I'm proficient with NEC 
modeling, it will ultimately come down to F/B observations while switching the 
array.

To get best performance, W8JI discusses the need to bond all coaxial cables at 
the top and bottom of the tower -- which I've always done for lightning 
abatement.  He also suggests running all control cabling on the inside of the 
tower.  The ultimate goal is to electrically break-up the tower such that a 
parallel resonant circuit is formed near the middle of the tower to make it 
"invisible" on 80m.  Of course, as the operating frequency moves from the 
parallel resonant circuit frequency, the tower starts affecting the pattern.

My initial thought is to create two wire skirts, one above and the other below 
a motorized vacuum variable cap.  The cap value can then be controlled back in 
the comm. shelter with a reversible switch -- or even by remote control over 
the internet with cap indexing reported back to the control point.

If anyone has similar ideas on how to detune a tower with ground-based 
adjustments, I'd like to hear about it.

Paul, W9AC

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of 
StellarCAT
Sent: Saturday, July 22, 2017 8:43 AM
To: TOWERTALK@contesting.com
Subject: Re: [TowerTalk] 80 M 4 SQUARE MODELING

you've got it - if that is indeed your only option - go for it! [but think 
about how you'd do the trick of breaking up the tower... in case the results 
are off measurably...John's book is handy for these things... ]

Gary
K9RX

-----Original Message-----
From: Bob Shohet, KQ2M
Sent: Friday, July 21, 2017 8:32 PM
To: cqtestk4xs@aol.com ; TOWERTALK@contesting.com
Subject: Re: [TowerTalk] 80 M 4 SQUARE MODELING

In 1995 I built an 80 meter 4-square with KQ2M design 3/16 wavelength spacing 
with 4 elevated  Inv L elements about 50’ vertical and the remainder mostly 
horizontal.  I used the Comtek phasing box and the antenna absolutely kicked 
butt!  In the 1995 ARRLDX CW Contest, at the low point in the sunspot cycle, if 
I remember correctly, I had more qso’s on 80 than any other US single op.

In 1999 I put up my 130’ Rohn 45 tower in the center of the 80 meter 4-square 
and populated it with 3  4 L 20 meter yagis.  The 4-square still worked well 
but not as well as before the tower erection.  Yes, that is anecdotal – but the 
effects were clear – the antenna was impacted by the tower and the yagis on it. 
 I was not as loud as before and the F/B and F/S were not quite as good.  It 
was noticeable to me on the air in the contest – I don’t know if anyone else 
would have noticed the difference.

I didn’t bother to model it – there was no other place to put the 4-square or 
the tower – you do what you have to do and put the antennas where they have to 
go.

Yes, the performance of your 4-square will be affected by the presence of the 
tower – but if that is the only place that your 4-square can go then don’t 
worry about it.  If you build it properly it will work fine and you will enjoy 
using it.  :-)

73 and gl!

Bob  KQ2M

From: Bill via TowerTalk
Sent: Wednesday, July 19, 2017 5:00 PM
To: TOWERTALK@contesting.com
Subject: [TowerTalk] 80 M 4 SQUARE MODELING


Now that I have finished my tower for 40-10 meters I need to start my next 
project.  I'm limited to the one 90 foot tower I have by county code.  I am 
planning on running 4 ropes from the last guy point (84ft) to install a wire
4 square for 80 meters.  Wires would be suspended vertically from the ropes in 
a typical 4 square pattern using Comtek switching.

Before I go through all the work installing the antennas and the radials
(yuch) I want to be sure the tower and all the antennas on the tower will have 
minimal effect on the 4 square.  I'm using Philly for the guy wires so that is 
not an issue.  I can mess with the HFTA program all day long and feel 
comfortable working with it.  However, this is not a project for HFTA and my 
computer antenna modeling skills are sorely lacking.

Is there anyone out there who could model this setup to determine if the tower 
and antennas will negatively affect the 4 square system.  I would be glad to 
share the exact details of the antennas, their heights, length of boom etc. off 
reflector to facilitate the analysis.

The 4 square is the only high performance system I can use out here due to the 
restrictions set by the county so any help on this would be appreciated.

73  Bill K4XS/KH7XS
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