At 05:42 PM 4/5/2006, Tom Osborne wrote:
>Yes, I meant they are in an equilateral triangle. Had a brain fart.
> Lots of postings on this subject, but nobody has yet answered my original
>question. I'll post it again.
>
>I have 2 stubs, separtated by a 1/4 wave phasing line on my single vertical.
>Will these stubs affect the phasing of the verticals. That was what I was
>originally asking. Thanks and 73
Coax stubs? Like the ones used as a trap for other bands? Or, are they
part of the tuning network?
Either way, they'll have some inductance or capacitance, and so, will
change the phase. The real question is how much.
How long are the stubs, are they open or shorted?
If you have Excel, download the XLZIZL spreadsheet from AC6LA
http://www.ac6la.com/xlzizl.html
You can enter in all the details of your transmission lines and stubs, and
run the numbers in a few minutes. XLZIZL won't do the full network
calculations with the mutual impedances, but at least you can see if the
"feed system" is reasonably flat over the frequencies of interest.
If you have multiple antennas and you want to understand the effects on the
system, there's 4 basic ways to go about it:
1) Build a NEC model, and use NT cards for your transmission lines and
stubs, putting in the appropriate numbers for your lossy transmission line.
2) Determine the mutual impedance matrix for the antennas (by measurement,
or by estimating with equations/tables). Build a model in one of the many
versions of SPICE out there (helps if you use one that does real
transmission lines).
3) Do the matrix calculations by hand (Yikes... but doable.. if you have
Matlab or Octave or Maple, this gets easier.. )
4) Measure it on your system. It's pretty easy to make and calibrate
current probes, and an inexpensive dual trace oscilloscope will let you
directly measure relative phases and currents.
Jim, W6RMK
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