See below:
From: <K7LXC@aol.com>
> C-51XR @ 120'
> Some 80 meter antenna @ 101' - probably a Magnum 280C, or if money or
> loading is an issue, an EF-180B
> C-31XR @ 90'
> C-51XR @ 60'
> C-31XR @ 30'
> Great idea but F12 says that 37 foot spacing is really the minimum;
>they'd prefer more for these longboom antennas.
>Cheers, Steve K7LXC
That's what I've heard they say. HOWEVER, if you model a pair of C31XR's in
EZNEC, to allow element interaction, rather than the abbreviated method used in
TA... then...
ONLY the 20 meter forward gain is better at 37 feet + , nothing else. The rest
of the optimums fall near 30 feet. And at those stacking distances, one is not
off 20 meter gain optimum all that much. I would love to see the particulars on
how Tom came up with the 37 foot minimum.
I'm not worried about the model being wrong, because it's quite close with a
single antenna to the figures he specs.
The problem with TA? Not a problem, just a trade-off to allow that program to
spend it's time worrying about terrain. The input to TA is a FREE-SPACE pattern,
already calculated. It uses a double of the free-space pattern inputted to
compute a stack. This does not allow for any interactions between the stacked
antennas or the ground image. There IS plenty of interaction.
At this point the LXC prime directive may yield less than optimum results.
- - . . . . . . - - . . . . - - . . - . .
73, Guy
k2av@contesting.com
Apex, NC, USA
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