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[TowerTalk] Resonant boom

To: <>
Subject: [TowerTalk] Resonant boom
From: "Jim Thomson" <>
Date: Sun, 24 Oct 2010 19:22:10 -0700
List-post: <">>
Date: Sun, 24 Oct 2010 11:03:25 -0400
From: <>
Subject: Re: [TowerTalk] Resonant boom

That interaction is incredible since the beams are 186' apart.   I don't 
recall my 60' boom yagis causing a 40m problem at my previous QTH with 20' 
spacing and I'm not sure yet if it's a problem at my new home with 75' 
spacing since the 40m beams are not yet connected.  I have modeled adding 
other antennas to my tower and saw  boom interaction.  I considered 
insulating the boom, but I have not tried this method.   Certainly grounding 
the reflector and last element would change the boom resonance, but not sure 
how feasible that is since the 20m beam is installed or if it would help.  A 
temporary fix is to use Green Heron controllers and link the two antennas 
together to ensure that they are pointing in the same direction when on 40m.

John KK9A / P40A

## Insulating his 65'  boom from the tower will accomplish nothing.  What's to 
avoided is floating 1/2 waves.....and  grnded 1/4 waves.    Right now, his 65' 
boom consists
of   2 x grounded  1/4 waves.... back to back.  You only need  ONE  1/4 wave 
grnded portion
to screw up a 40m ant...and he has 2 of em.   See my previous post.   His boom 
will  have to be
de-tuned  by one of the methods that folks have described. 

##  for folks with yagi's on rotating towers, boom interaction is a non issue.  
The problem starts
when side mounts and tic-rings are used.    Or in this case, when a resonant 
boom on one tower, 
interacts  with a 40m yagi.... 186' away.   186'  sounds like a lot.... but is 
only 1.32 wave lengths 
on 7 mhz. 

##  syncing 2 x GH box's  would be a temp fix.  He may not want 20 +40m pointed 
in the same direction
all the time.   At night, if little 20m activity, and on 40m, linking the 2 x 
rotor's  would be doable. 

##  BTW,   I have the small K7NV prop pitch + deluxe mast clamp..+  GH box.  I 
also have 2 x OR-2800's
and 2 x TIC rings [ one is analog, other is digital].   The GH box is clearly 
the winner.  The m2  OR-2800 control
box is more awkward to use, and has NO ramp down, when using the front panel 
cw/ccw controls in manual
mode!   The M2 control box has No  point and shoot knob.  M2's  eq of point and 
shoot consists  of manually
bring up a new heading, then rlsing,then it starts the ramp up/down procedure.  
 While both my tic rings have 
point and shoot knobs... neither has ramp up/down capability,  which clearly 

## I  have the real old, early SN  RT-20  GH box...which is also tweaked up for 
the small PP [27 vdc@ 10A CCs output only],
and was not happy  with some aspects of the ramp down, depending on V drop to 
PP.   K7NV  copied  everything 
to Jeff @ GH..and the easy fix was to just install the new RT-21 processor chip 
[$25.00]..and now it's a RT-21...
problem solved.   Having a desk full of GH box's, that can control any rotor 
made,and that also 'talk' to each other
is a huge bonus.   You now have a standardized control box. 

later.... Jim   VE7RF 


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