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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