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Re: [TowerTalk] Sigma 180-S / 280-S

To: <>
Subject: Re: [TowerTalk] Sigma 180-S / 280-S
From: <>
Date: Mon, 11 Oct 2010 22:18:41 -0400
List-post: <">>
The 40m OptiBeam decoupling stubs apparently make the antenna resonate 
outside the ham bands (except for 40m obviously) but they do not make the 
antenna invisible and you still need to use reasonable spacing (8-9 foot) to 
other HF antennas.   The 80m shortened beam may already not be resonate on 
any other ham band and therefore not need stubs.  I had no noticeable 
interaction between my homebrew linear loaded 80m dipole and a 20m beam and 
40m beam.

John KK9A

To: <>
Subject: [TowerTalk] Sigma 180-S / 280-S
From: "Jim Thomson" <>
Date: Mon, 11 Oct 2010 07:11:14 -0700
List-post: <">>

If anybody owns either  a F-12  Sigma 180-S or  280-S.[ both 80m ants].. or
knows somebody who does own
either one,  perhaps you could stick a few watts into  it on 20m, and see 
kind of swr
you have on 20m.    If you have the time, perhaps sweep it with a MFJ/etc, 
see where it
does resonate.  Not all these ants  will resonate on their 3/5th harmonics.
The F-12  340-N  [3-el 40m yagi]
does not resonate on 15m.... it resonates  just below the 12m band.

What baffles me is  3.5 x 3 =  10.5 mhz.     10.5/14.2 =  .74       The 80m
ant, on it's 3rd harmonic is
26%  lower in freq than 20m.     I have heard several horror stories now of 
arrays  completely
screwing up 20m yagi's that are in close proximity.  Rotating the 80 + 20m
arrays , so their booms are
90 deg to each other does not always work.    The 35' booms  used on both 
280-S and 340N   will screw
up 20m real fast.

I noticed that Optibeam uses decoupling rods on their 4-el 40m  yagis.  They
won't screw up a 15m yagi, nor
another HF array.   Does anybody know how this is done ?   Can this 
be adapted to an 80m array ?

Jim   VE7RF 


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