[Top] [All Lists]

Re: [TowerTalk] Phasing verticals and stubs

To: "Tom Osborne" <>,"Towertalk" <>
Subject: Re: [TowerTalk] Phasing verticals and stubs
From: Jim Lux <>
Date: Thu, 06 Apr 2006 06:33:24 -0700
List-post: <>
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

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 


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>