[TowerTalk] Antenna Analyzers

Wed Dec 5 15:00:21 EST 2018

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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