[TowerTalk] Interaction Issues

[john at kk9a.com]

I did not suggest changing the coax length, the original post said that he changed the phasing by 90 degrees.  I later read he meant that he rotated the 6m beam 90 degrees.  I am not sure why he rotated the antenna now after it was previously in line with the C3.  In my experience from modeling my antennas this often makes interaction worse.

 

John KK9A

 

 

From: Chuck Dietz [mailto:w5prchuck at gmail.com] 
Sent: Sunday, April 09, 2017 1:22 PM
To: john at kk9a.com
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] Interaction Issues

 

No reason to change the coax length, check the coax itself by disconnecting and putting an analyzer at the remote switch on the tower, if there is one. 

 

Chuck W5PR

 

On Sun, Apr 9, 2017 at 11:29 AM, <john at kk9a.com> wrote:

Phasing will have no effect but I am not sure why you would change the coax
length. If the 6m beam is 90 degrees to the C3 and the 6m boom length is
around 1/2 wl on 20m or less than that but electrically 1/2 wl due to
grounded elements there will be serious interaction.

John KK9A

To:     "towertalk at Contesting.com" <towertalk at Contesting.com>
Subject:        [TowerTalk] Interaction Issues
From:   Jeffrey Cantor <k1zn at att.net>
Reply-to:       Jeffrey Cantor <k1zn at att.net>

I recently had some tower work done.  Ihave a Rohn 25 tower up 60 FT.  I
have
a C-3 and a 6-element Cushcraft 6Mon it.  Both antennas were doing fine -
SWR
essentially flat on the C-3and around 1.5:1 on the 6M.  They were both
mounted
on a 9 FT mast,separated by about 6 FT. The job was to replace the 9 FT mast

witha 15 FT lighter mast and to install a new 12/17M WARC Cushcraft antenna.

The new setup had the 12/17M antenna atthe top of the mast; the 6M in the
middle, phased at 90 degrees to the otherbeams - - separated by roughly 6 FT

between it and the lower C-3 and the WARC. After the install, I am noticing
a
2.0:1. 2.4:1 SWR on the C-3 on 20M only; 15M & 10M are OK.  On the 6M -3.0+

SWR. Do I have an interaction problem betweenthe 6M and C-3? Should the 6M
be
at the top of themast?  Offset to the others, or not? Jeff/ K1ZN

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