Date: Sun, 24 Oct 2010 11:03:25 -0400
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'
of 2 x grounded 1/4 waves.... back to back. You only need ONE 1/4 wave
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
TowerTalk mailing list