I made comments directly to Doug, at his first posting, and said that this
thread would
again get legs. :)
So let me repeat some of my comment, for those who didn't see it the last time.
1) I've had several LPDA's, the T8 being the best of them. It's head and
shoulders
above most trapped tribanders on short booms. The F12 C3S may be an exception,
It's pretty good.
2) I changed from LPDA to a 3 el SteppIR, and was extremely pleased with its
performance.
It was a 3 el, and sure enough, results were like going from a 2 el yagi with
the lpda
to a 3 el with the steppIR. No magic there.
Band change, with the Icom interface, was very fast. It took
approximately
2-3 seconds for the computer to command the rig, amp, and antenna to switch
over.
Barely enough time to get a sip of coffee, before calling the station I was
chasing.
(I like to use the bandmap in small station contesting, in a point & click
mode.)
3) Stacking Log Periodics:
An interesting topic. And one which seems worth experimenting, to me.
I started to, but got wrapped around the axle:
With two T8's, each with 16' booms, you can put the front elements half wave
apart
at 28MHz, and the rear elements half wave apart at 14 MHz. The upper antenna
tilts downward and the lower antenna tilts upward. I don't recall the angle,
at this point,
something like 22.5 degrees. My plan was to mount the lower antenna with the
longest
20m element at 36', and the upper 20m reflector at 70'.
I went so far as to buy two blank mast-boom plates from Tennadyne, and have
them
locally drilled for the calculated tilt angles. I was in process of
designing the In/Out of
phase system, which can be done fairly simply with a single relay, given the
transmission line boom
feed system for the T8.
Somewhere in there, I got bogged down trying to model the thing. Cebik also
got
bogged down modelling it. Healthy discussion followed. I was about to buy
the second
LPDA and get on with my empirical approach, when a hurricane blew through,
took out
a big oak tree, which took out my tower. Then I got transferred.
The feeling was that tilting the antennas would tend to raise the radiation
angle, at the
heights we were talking about. If I could have put the lower one at 70' and
the upper
at 100, it might have been different. That's what we had hoped to model.
I still think this would be a worthy experiment--but not one I can pursue in
suburbia.
N2EA
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