Date: Thu, 01 Sep 2016 09:09:50 -0400
From: Roger D Johnson <n1rj@roadrunner.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 6 mtr quad
The big question is, over what frequency range and angles does this FB ratio
hold up?
73, Roger
## good question. If the take off angle is say 10 degs..with a 20m quad up
100 ft high, the FB will also be max, say 30 db.. at 10 degs, but may well
drop like a rock, with higher angles. So local, high angle stuff directly
behind you could
easily be a lot louder than you think.
## I managed to get 45 db FB over a huge chunk of 20m, and 25 db fb on each
end,
using YO-7.3 years ago. I was not interested in CW, nor above 14.300 khz,
so it was
optimized for 14.100 to 14.300 1st modeled in free space, then above ground
at 75 ft.
## This was FB.... as in 180 deg flipped. These days FR is used. Yagis
tweaked for
max FB, 180 degs behind the ant, usually end up with a lobe on either side of
the 180 deg point.
## So yeah your 30 FB may well be only 20 db FR when you factor in side
lobes off the rear of the yagi.
How many times do you have QRM, that is exactly 180 degs from the station u are
trying to work.
## The ants that have a sharp null that is 180 degs... require a rotor that
can be slowed way down, almost
like trying to tune a sharp notch filter. 1 rpm is way too fast to tune for a
null.
Jim VE7RF
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