Thanks. Just a couple of clarifications.
The original Touchstone software was by EEsof. I had a copy at Hughes in the
early 1980s. It was of course a DOS program and came with a parallel port
dongle for security. HP had nothing to do with it.
The RigExpert operating under AntScope can export Touchstone files in three
different formats.
Wes N7WS
On 12/5/2018 1:00 PM, Jim Brown wrote:
Thanks for this excellent summary, Wes. The only ones you've reviewed that I
own are the SDRKits VNWA and the FA-VA5. I don't find the UI of the FA-VA5
quite as awful as you do, but it certainly could be improved.
I often export data from antenna measurements to AE6TY's excellent SimSmith
software to design matching networks and compute feedline losses. This
requires a Touchstone file, which is a plain text format developed by HP years
ago for data interchange. DG8SAQ's VNWA software, which supports the N2PK and
FA-VA5 analyzers as well has his own, the VNWA built and sold by SDRKits
produces Touchstone files. A friend owns a Rig Expert unit that does not
produce Touchstone files, but does produce a file that ZPlots can read, and
ZPlots can export that data as a Touchstone file.
Another important point is that while many of the modern analyzers can do TDR
to measure the length of transmission lines and find splices and faults, the
VNWA software is particularly good at this. You make a wide sweep of the line
(I most often use 100-500 MHz), and the software does an inverse FFT of the
data to convert the measured frequency response to the time response, and
gives the user to select five different windowing functions and three
different excitation pulses, all of them post-processing measured data. This
allows the user to select the windowing function that provides the best view
of the data, and to use an excitation that displays the impedance of each
segment of the line being measured!
I've recently completed the first phase of a study to use S11 measurements of
the impedance of 2-turn chokes wound on 2.4-in toroids to characterize them
and to identify them by their "mix," the number assigned by Fair-Rite, the
manufacturer of most ferrite cores we use. Two turns was chosen because that
puts the choke's impedance within the 5:1 - 1:5 ratio to the 50 ohm system
impedance where Z measurement has the greatest accuracy. A quick summary of
that work is at k9yc.com/2TurnTests.pdf
It should be noted that VERY careful calibration of the analyzer is required
for these measurements. It took me three tries to get to the end of the
alligator clips where the test chokes were connected. I did these measurements
with DG8SAQ's VNWA software controlling the FA-VA5 analyzer. The clips are
plugged onto the ends of a BNC to male Pomona (double banana) adapter, which
is attached to a 5 ft RG142 BNC to BNC cable. I accomplished the calibration
by adding a pair of BNC to N adapters to the cable for calibration, thus
lengthening the cable to approximate the added length of the clips and BNC to
Pomona adapter. The apparent resonance around 29 MHz in some of the choke
measurements is the result of the calibration starting to lose accuracy.
73, Jim K9YC
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