----- Original Message -----
From: "Rick Karlquist" <email@example.com>
To: "Jim Lux" <firstname.lastname@example.org>
Cc: "Robert Shohet" <email@example.com>; <firstname.lastname@example.org>
Sent: Sunday, June 13, 2004 6:02 PM
Subject: Re: [TowerTalk] 80 4-square inside a 160 4-square? Pros and
> Jim Lux said:
> > We need to create those same tools for other antenna configurations, and
> > phased arrays in their many forms are probably a good place to start.
> > longer should the computational complexity be a reason to avoid
> > designs. Synthesizing and analyzing complex networks of 20 inductors
> When I built my first 7 hex array, I measured the impedances and
> compared them with EZNEC. They were considerably different. Fortunately,
> the phasing network has one adjustable coil and one adjustable capacitor
> which are empirically adjusted for correct phasing. It would be
> a nightmare to have to measure a 7x7 matrix of coefficients and
> synthesize 7 arbitrary networks.
I'm not surprised they were different from the model.
A nightmare, with typical ham tools as they sit today. Just like trying to
build and design a yagi in the 1950's with a vacuum tube grid dip
oscillator. And, as you say, adjustment in-situ is the real answer. What's
needed is the equivalent of something like one of the antenna analyzers
designed for phased arrays.
I've seen references to a ham-style network analyzer from Alpha (in ON4UN's
book) but haven't ever found anything more. I have great hopes for using
something like a SDR-1000. Sure, it's a $500 widget, but people spend a LOT
more than that on antennas.
And that's just for one frequency.
> You start all over again if you QSY from phone to CW. OTOH, my
> 2 element phasing network can (and eventually will) be servoed by
> a simple phase/magnitude controller that is very similar to an
> autotuner. In fact, I am going to convert a military autotuner
> for this purpose. This is not a tools issue; you have to physically
> build all this stuff, and computer tools aren't going to do that
> for you.
Hopefully, over the next decade(s), people will start making tuners and
software that do this. People like LDG are contemplating building "remote
controlled" versions of their tuners (rather than autotune), which would be
a good start. For now, though, as you say, it's up to the individual user
to fabricate stuff. I modified a batch of 10 LDG QRP tuners for just this
sort of application, although my efforts have stalled for lack of time and a
good measurement technique to tell if it's working. I've been looking at
those nifty USB measurement pods driven by some appropriate current sensors
at the elements, etc., but haven't worked out how to do the vector current
measurement easily and cheaply.
In theory, one could probably use standard Fwd/Rev couplers (like used in
remote SWR heads) and calculate, particularly if you can run the tuners
through a series of known states, so you can probably solve the equations
for the mutual Z.
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.
TowerTalk mailing list