On 2/24/2014 6:56 PM, George Dubovsky wrote:
The N2PK design is a well-regarded piece of kit, and I built one about 4
years ago. It compared very well with the HP 8753 VNA I had on my bench at
work back before I retired. It has a very enthusiastic following worldwide,
surprising for something that is only available as a fairly complicated DIY
effort.
I've heard the same universally good things about it, but last not easy
to acquire -- last I heard, you've got to build the board, buy the parts
and build it. I tried to do so several years ago without success.
However -- by all means look at the VNWA designed by DG8SAQ, nicely
built by a UK ham. $700 delivered to my mailbox with calibration kit.
Does simultaneous S11 and S21. Full spec to 500 MHz, reduced dynamic
range to 1.3 GHz. Software is by DG8SAQ, who is a prof at a German
university, and the softwae is still being actively developed. One VERY
nice feature is that it is powered from a USB port -- no need to drag
120VAC for power. Runs quite adequately with my 10 year old T41
Thinkpad. Also does TDR and works as a spectrum analyzer. Support is via
a reasonably active email reflector, which DG8SAQ reads regularly. I've
been using mine for nearly 2 years now and am quite pleased. I bought
the carrying case, which was a mistake. You want the 3E with everything
but the case.
http://sdr-kits.net/VNWA3_Description.html
If you know what you're doing, it's easy to make Z and TDR measurements
of an antenna in the shack, find Vf of the transmission line at the
frequency of interest, and send the Z measurement to SimSmith software
(freeware by AE6TY) to transform the data to the antenna terminals,
design matching networks, etc.
The VNWA 3E was about to get a glowing review in QST a few years ago,
but the guy who sells the AIM products queered it by threatening a
patent fight.
73, Jim K9YC
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