A few years ago I did a lot of computer modeling in trying to figure out the
best spacing for a 2-high stack of C-3E tribanders. In the process I
discovered a couple of things that may be relevant:
-- compromise spacing is just that, and even over a 2:1 frequency range there
really is no decent 3-band compromise, so the problem with a 2-stack on
MonstIRs is truly compounded. I would up compromising between 20 and 15.
-- there are some quirky sweet spots for F/B ratio. For example, a 2-high
stack of C-3Es on 20 has F/B of only about 11-12 dB, but at 36 foot spacing, my
models show that the stack exhibits 26 dB F/B over a relatively narrow
frequency range at the bottom end of the band. I was tempted to move my lower
yagi from its original 28-foot compromise spacing to 36 feet, at least for the
remainder of the sunspot minimum, but the modeling doesn't show a comparable
"sweet spot" for stacking gain. I often find that low F/B isn't *that* big a
handicap, and it would have been a lot of hard work, so I left things alone.
73, Pete N4ZR
At 09:27 PM 3/9/2007, Cqtestk4xs@aol.com wrote:
>In a message dated 3/10/2007 2:22:06 A.M. Greenwich Standard Time,
>Your comment brings up a good question, as a general rule,
>does stacking yagis typically result in a lower overall F/B
>of the array? I wouldn't think so. If done correctly array
>gain goes up and I expect array F/B to also improve.
>I found that my 2 high and 4 high stacks suffered in the F/B area. However,
>my QTH was in FL so F/B was not much of a problem, since the back was
>usually Africa, VK/ZL and South America....not all that much of a problem for
>signals off back of a stack, and sometimes very handy for a juicy mult to call
>The same will be true in KH6 with my new station...not much off the back
>when facing JA, W or EU.
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