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
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 ?
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