On 4/3/2023 10:20 AM, Tree wrote:
I guess most people have some kind of small antenna analyzer that has a TDR
kind of function.
In my professional life in pro audio, I started doing Time Domain
Spectrometry in 1982, so I have a pretty good handle on how it works.
There is a mathematical relationship between the frequency response of a
system and its time response -- one is the inverse of the other. The
Fourier Transform of the time response yields the frequency response,
and the Inverse Fourier of the frequency response yields the time
response. Modern antenna analyzers produce a swept frequency response,
and associated software running on the computer does the Inverse Fourier
Transform of a sweep to produce the TDR.
For more than 10 years, the best of the low cost Vector Network
Analyzers has been the VNWA3SE, built and sold as a finished and tested
unit, by SDR Kits, run by hams in UK. The unit, its firmware, and
associated software, was designed by DG8SAQ, an EE prof. Support from
both DG8SAQ and SDR Kits is excellent -- both read and respond to their
support email reflector. Current cost with shipping is about $560
(depending on currency).
https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3
Greatest precision (ability to see small things) is provided by a sweep
over a very wide frequency range. I usually sweep from 50-500 MHz. Once
the sweep is done, the TDR is simply a few more button pushes in the
menu system.
73, Jim K9YC
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