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
On 12/5/2018 7:21 AM, Wes Stewart wrote:
A recent post about a new toy led to some discussion about readily
available antenna analyzers that meet the special needs of Topband
aficionados who have to cope with big BC band signals affecting their
measurements.
I mentioned several that I had on hand at the time and another about
to arrive. The new one is here and a quick measurement on my 160
inverted-L in the presence of a 1550 kHz 50KW station 5 miles away is
positive. Here is a short overview of the different units.
All of these have some things in common. They can all be "calibrated"
using Open, Short and Load (OSL) standards. This provides the
opportunity to calibrate at the end of a cable or in another connector
series. They all display data in multiple formats and offer some form
of data storage.
1) The N2PK by Paul Kicaik AFAIK started the whole genre of portable,
amateur built vector analyzers that use PC computing power for data
calculation/presentation. (http://n2pk.com/#TP1) Originally, used a
parallel port interface, later ported to USB. First software ran under
DOS. Several contributors built Windows software. Still an excellent
device for Topband guys, but limited frequency coverage. This is a
two-port vector analyzer, so it would be good for characterizing
phasing lines, feed networks and filters as well as antenna impedances.
2) Short of an HP-8510, 8753 or 3577 the gold standard for hobbyist
use IMHO is the SDR-Kits, DG8SAQ designed VNWA.
(https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3) This is also a
two-port vector analyzer. The VNWA software is *very* powerful, with a
commensurate learning curve, and is well supported by the author
Dr.Tom Baier as well as some very knowledgeable users. A bit
difficult to operate in the field because it's tethered to a computer,
but I have done it. This is a lab grade instrument. Uses SMA connectors.
3) The Rig Expert line of analyzers are one-port, standalone
instruments. (https://rigexpert.com/) They are well-suited to field
work except for some difficulty reading the screen in sunlight. I
have the AA-55 Zoom version. Data can be saved internally and read
out into their AntScope software via USB. For further manipulation,
s-parameter files can also be read by Zplots. Unit can also be
operated as a test head over USB using AntScope. This is totally
independent of what is on the screen of the instrument. The software
version I have is buggy and adds a bogus data point at the end of the
data file. I've reported this and there is a newer version that might
fix this but the colors chosen for the screen are nearly unreadable
and the program structure is a mystery to me. Uses a "UHF" connector
and is powered by two standard AA cells and/or USB.
4) The FA-VA5 by DG5MK is a very compact standalone instrument with a
lot of features. (https://www.sdr-kits.net/VA5_Page) It is an easily
assembled kit. For field work the screen is very readable in
sunlight. Unfortunately, it is plagued with a horrible interface,
just three push buttons. This can also be used as a one-port test
head under the DG8SAQ VNWA software with all of the attendant power,
and complexity. Again, this is totally independent of the internal
calibration, etc. Uses a BNC connector and is powered by two AA cells
and/or USB.
5) The FAA-450 by EU1KY is a work in progress.
(https://bitbucket.org/kuchura/eu1ky_aa_v3/wiki/Home) This one is
unique in that the standalone interface is a color touchscreen.
Originally conceived as a DIY project it is now offered in various
stages of kit or a completely assembled unit. I purchase the
completed unit, which as it turns out is built in China. The enclosure
is a robust, albeit somewhat clunking arrangement of flat plates keyed
with tabs and slots. Firmware is open source. The complete unit comes
ready to use with EU1KY firmware installed. I've installed supposedly
more useful firmware by DH1AKF. I've found a couple of hiccups in
this so far, so the jury is still out. There are a couple of
different USB interfaces. With the correct drivers, the unit can be
operated with the Rig Expert AntScope software. Uses a type N
connector and a Li-ion cell, rechargeable over USB.
I'm sure there are others but these are the ones I own and have
experience with.
Wes N7WS
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