[TowerTalk] Interaction Issues

[john at kk9a.com]

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