[TowerTalk] Antenna Analyzers

[Wes Stewart]

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