This sort of works... (I've tried it, both real, and in extensive
simulation)
A couple aspects that will bite you:
1) The optimum takeoff angle changes, so the optimum phasing changes. No
problem, if you're willing to continously adjust. I'm actually not sure
that adjusting small changes is really worth it for the few tenths of a dB
you'd see.
2) Swapping in lengths of coax doesn't necessarily give you the
corresponding phaseshift. If you have any mutual interaction between the
antennas, then the feed point impedances will change, which will change the
effective phase shift.
3) There was a nice writeup of a similar idea in one of the ARRL antenna
compendiums using a pair of verticals a fair distance apart. He used a Pi
or T network for the phase shifting. The adjustment method was quite
elegant. Hook them up out of phase, adjust for the null, then reverse the
phase on one.
4) A network to do continously variable phase shifts is probably nicer in
this application than an incremental relay/coax scheme. More compact, and
lends itself more to tweaking.
----- Original Message -----
From: "Tom Sessions" <k4rv@mindspring.com>
To: <towertalk@contesting.com>
Sent: Sunday, September 26, 2004 9:53 AM
Subject: Re: [TowerTalk] Phasing stacked tri-banders (or,"can you check my
homework?")
> Could incremental lengths of coax be used to phase two different antennas?
>
> Just suppose I have a brand M 4 element monobander and a brand H 6 element
> monobander, each for the same band, stacked on a rotating tower. I have
no
> idea of the length of the feedline to each and I want to feed them
together
> for biggest DX signal.
>
> Could I add coax increnentally to one of the feedlines, and then transmit
a
> signal thru both simulatanesously to be received at a distant ground wave
> station in order to determine how much extra coax would bring the signals
> from the two antennas into phase. I am thinking that the length of extra
> coax yielding the strongest received signal at the far station would
> indicate proper phase for DXing.
>
> Lengths of 1/10 wavelength, 2/10 wavelength, 4/10 wavelength and 8/10
> wavelength, just four lengths of coax, would incrementally cover every
> tenth of a wavelength for the experimental coax.
>
> Anybody tried this?
> Comments?
> Suggestions?
>
> thanks/73
> Tom K4RV
>
>
>
>
> _______________________________________________
>
> 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 and ask for Sherman, W2FLA.
>
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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
and ask for Sherman, W2FLA.
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