OptiBeam uses stainless steel wire for the stub. It seems to work, one of
my 40m beams has a 15m beam above and below it and I see no interaction.
The SWR remains constant when rotating it. When installing the 40m
OptiBeam you have to use caution not to get these wires caught in other
antennas, once installed it should hold up fine. I have modeled the OB2-40
without the stubs and I still see no resonance on 15m, however I am not
an antenna design guru. I agree that it would be good practice to design a
40m antenna that is not resonant on 15m.
John KK9A
[TowerTalk] Changing interaction of M2 40M4LLDD on 15
from [Jim Thomson] [Permanent Link][Original]
To: <towertalk@contesting.com>
Subject: [TowerTalk] Changing interaction of M2 40M4LLDD on 15
From: "Jim Thomson" <jim.thom@telus.net>
## so why doesn?t M2, just build the damned thing right the 1st time ???
Optibeam uses decoupling stubs on their version of their 4 el 40m yagi.
One
on each side of boom,
so 8 x stubs in all. The stubes on the optibeam appear to be small gauge
al,
coming out from the 40m els..at at right angle for a couple of inches, then
parallel to the ele for a
couple of feet. Far end of stub is held in place with a small insulator
back
to the ele. You can see the concept on their install manual. Done right,
the 40m yagi can be very close to
a 15m yagi. These ants have to resonate some where, so the resonance
will no
doubt be shifted higher up in freq.
## F12s N series of 40m eles, on their 1-2-3 ele 40m ants.... don?t resonate
on 15m. However they will resonate on aprx 24 mhz...which will screw up
a 12m
yagi. f12 claims their N series of 40m
arrays can be within just 3 feet of another F12 monobander or
tribander (
20-15-10m). F12 didn?t use stubs. They used longer eles, ranging from
aprx 59 feet for the ref to 51 feet for the
dir. Longer eles + LL rods.
## This 40m yagi and interaction to a 15m yagi has been an issue for
decades
now.....and is easily resolved. Dunno why the folks at M2 have not
figured it
out...yet.
Jim VE7RF
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