[TowerTalk] Sigma 180-S / 280-S

[Jim Thomson]

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  what kind of swr
you have on 20m.    If you have the time, perhaps sweep it with a MFJ/etc,  and 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 80m 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 the  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 technique be adapted to an 80m array ? 

Jim   VE7RF