[TowerTalk] 80 M 4 SQUARE MODELING

Sat Jul 22 09:25:44 EDT 2017

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 at contesting.com] On Behalf Of StellarCAT
Sent: Saturday, July 22, 2017 8:43 AM
To: TOWERTALK at 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 at aol.com ; TOWERTALK at 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 at 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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