Placing antennas at right angles often worsens interaction problems. There
should be little interaction between 40m and 80m if they're pointing in the
same direction, but who knows what interaction the boom will cause if one is
rotated. The only way to tell is to take the time to model the system -
modeling software is very inexpensive. Your perposed spacing is very
close and your mast has a lot of antenna load, hopefully it's not a 2" mast.
Subject: [TowerTalk] Min spacing to 80m yagi ?
From: "Jim Thomson" <email@example.com>
Date: Wed, 6 Oct 2010 05:34:21 -0700
How close can you get a 20m yagi, below a 2-el 80m yagi ?
I have an option to use a F-12 Sigma 280-S shortened 80m yagi
at the top of the mast, with the F-12 340N at the bottom of the mast.
Spacing between the two of them would be 10.5' If possible, I
would like to sandwich my F-12 520 [20m yagi] between the
80 and 40m yagi. Apparently, you can mount any other F-12 HF
yagi within 36" of the 3-el 340N yagi. If I put the 20m yagi
4' above the 40m yagi... that would leave 6.5' between the 20m yagi
and the 80m yagi. Will this work ?? If it doesn't, one option is
to remove the 20m yagi. Another option is to place the 80 and 40m
yagi's at right angles to each other [ no 20m yagi at all] . I don't think
is required, but would minimize the total wind load.
Plan B would be to replace the 2-el 80m yagi with a
80m rotary dipole...with dipole inline with 20m/40m booms below it. IE:
is then at right angles to both yagi's below it. Due to day time height
the above options are strictly an after dark scenario. I don't have any
software on hand
to model any of the above.
Thanks.... Jim VE7RF
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