Topband: Handheld Impedance Analyzer
jim at audiosystemsgroup.com
Sun Mar 27 15:40:07 EDT 2016
On Sun,3/27/2016 12:08 PM, dick.bingham wrote:
> I certainly do not want to restart this topic but new stuff is becoming available and I don't want to settle for second best if 'best' is not 2X more costly!
I don't have time to write off-list replies to questions that have
general interest, so I'm responding on the list. I suspect that the
solution to your problem is a combination of 1) better understanding of
your antenna design, which is generally aided by study of books like the
ARRL Antenna Book and the ON4UN book; 2) decent measurement hardware;
and 3) comparing measured results with the model, using free software
like AE6TY's SimSmith and AC6LA's ZPlots (a freeware Excel spreadsheet
that runs only in Excel, not in freeware clones).
My "quick and dirty antenna analyzer is still a 10+ year old MFJ-259B. I
also own an even older AEA sweep analyzer that can be jumpered for 75
ohms, and I have it set that way to measure 75 ohm feedlines.
My really good one is the VNWA 3e, designed by German prof DG8SAQ, built
and sold by hams in the UK. All the heavy lifting is done in a laptop
connected via USB, and the VNWA is USB powered. The VNWA software links
to ZPlots, which can transform a measurement made in the shack to one
made at the antenna itself. And the VNWA can do a TDR of the line to
tell ZPlots how long the line is that must be transformed, and can
measure to very good precision Vf, Zo, and attenuation vs frequency of a
sample of the coax in use. For those who may have slept through
Transmission Lines, Vf, Zo, and attenuation all vary with frequency, and
the variation is greatest at lower frequencies. This is all predicted by
the transmission lines equations. I paid about $750 for my VNWA three
years ago, including a calibration kit, a cheesy carrying case, and
shipping to my door in W6.
The VNWA, like most serious vector analyzers, can generate data files
for export to programs like SimSmith and ZPlots, which can then be used
to design matching networks, stubs, etc. And the VNWA is well supported
both by a Yahoo Group that is monitored daily by DG8SAQ, the hams who
sell the unit, and a fair number of smart and helpful users.
73, Jim K9YC
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