[TowerTalk] 6 mtr quad

[Jim Thomson]

Date: Thu, 01 Sep 2016 09:09:50 -0400
From: Roger D Johnson <n1rj at roadrunner.com>
To: towertalk at 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