In a message dated 11/24/2005 10:00:45 A.M. Pacific Standard Time,
Force12Talk-request@qth.com writes:
> I am TRYING to "tune" a 240N (height is 25') and am not getting
reasonable
results. Tom is not sure why. He says the factory default lengths for the
reflector and the driver should work but I am much shorter than this (5.5"
on each tip on the reflector and ~3.5" on the driver element) AND the
bandwidth is bad (~ 180 Khz - should be almost 300). Can someone please
help?
> Does anyone know how many turns the hairpin match has? I do not think I
got
one (or I misplaced it) and I made one that is 2.5" in diameter and 3 turns.
Since the hairpin (made into a coil) is part of the element length, it's not
too critical in length since the jumpers can (will) be adjusted to resonance
anyway, rendering the hairpin length simply relative.
> Did you tune yours or just set it to a length?
You have to tune each element to resonance (the REF and DIR resonances are
in the manual). I have NEVER seen an F12 linear loaded antenna be set
correctly when using the manual dimensions - they're just a starting point.
> What length did you end up with (for the tip sections) on the reflector?
On
the driven element?
I've always just adjusted the LL jumpers and didn't worry about any other
part of it.
> What is the swr bandwidth for a 2:1?
For the F12 LL antennas I've worked on - a couple of dozen - it's been about
180 khz. I think there were only a couple of N types in there.
> I checked the driver alone (reflector jumper removed) and still the SWR
for
a 2:1 is only about 180Khz.
Sounds normal to me.
Cheers,
Steve K7LXC
TOWER TECH -
Professional tower services for commercial and amateur
Cell: 206-890-4188
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
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