[TowerTalk] 80 M 4 SQUARE MODELING

[StellarCAT]

I modeled a 160 meter vertical, 100' tall (it was modeled with wires coming 
off the top for 160 match) and a 4 sq for 80 around it. It showed severe 
coupling in to the 160 tower from the 80 antenna.

I also tried a 130' vertical - that would have required breaking up the 160 
in 2 places in to 3 sections.

Modeling what you are talking about would be very difficult because of the 
fact that those antennas rotate. My suspicion is that the antennas 
themselves other than acting to effectively lower the resonant frequency of 
that main structure, won't have too much of an impact. Its that center tower 
that gets in the way.

That stated as others will attest it has been done - and some will suggest 
they work very well although anecdotal evidence is really hard to weigh...

Note my model was not using vertical dipoles - it was using the center tower 
as support points for verticals coming off the ground for 80. Perhaps that 
makes a significant difference.

Gary
K9RX

using a basic 4 sq model (supplied with the ARRL AB) I see just under 5.8 db 
gain and 25 db FB.... when I introduce a 135' vertical in the center the 
gain drops to 5.16 and the FB to 7! Note also the peak angle of radiation, 
the most important factor, goes from 23° to 30°! At THAT angle the gain is 
5.46 and FB 10 db.

So it all comes down to what that center looks like overall! If it is 
resonant anywhere near it will 'such' energy ... and you'll need to detune 
it. Possibly in more than one place!

change that center to 120' and it is 6db and 11.4 db fb
to 90' and it is 5.9 db and 21.4 db FB.





-----Original Message----- 
From: john at kk9a.com
Sent: Thursday, July 20, 2017 7:05 AM
To: TOWERTALK at contesting.com
Cc: cqtestk4xs at aol.com
Subject: Re: [TowerTalk] 80 M 4 SQUARE MODELING

I modeled 2 and 4 free standing verticals around my 80' tower and saw no
serious issues so I imaging that this will work. K9RS has a nice article
on bent wire low band verticals around his towers. Don't be intimidated by
modeling software, it a great tool to have.

John KK9A


To: TOWERTALK at contesting.com
Subject: [TowerTalk] 80 M 4 SQUARE MODELING
From: Bill via TowerTalk <towertalk at contesting.com>
Reply-to: cqtestk4xs at aol.com
Date: Wed, 19 Jul 2017 17:00:46 -0400


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