Looking for a single hard fault the FA-VA5, you can look at the coarse
frequency response first, and them zoom in on the exact frequency of
each of the consecutive opens (or shorts) separately using a narrow span
to get adequate frequency resolution because you know from the coarse
sweep that there is nothing interesting happening in between. Or I guess
you can drag a computer along and run VNWA and get TDR in real time (I
haven't tried that yet).
73, Mike W4EF....................
On 11/6/2021 7:42 AM, Lux, Jim wrote:
On 11/6/21 7:30 AM, Michael Tope wrote:
You can save raw impedance data to memory on the FA-VA5 while using
it standalone in the field and then download it later to the VNWA
software. The one frustrating limitation of using the unit standalone
is that you are limited to 101 frequency points per memory register
(IIRC, the unit has 10 memory registers). For typical antenna
impedance measurements, that is fine, but for TDR measurements, it
can limit resolution. You can get around this somewhat by saving
sub-segments to different memory registers and then combining them
after download. In theory this would allow you to achieve the
equivalent of saving 1010 frequency points while using the unit
standalone.
I've been fooling with 101 point TDR and a NanoVNA recently - you can
actually get finer resolution with interpolation (zero pad the data
before transforming, is one way). The constraint is that there are
potential ambiguities. And it depends on the SNR. And, if there are
multiple faults, then life gets more complex.
Someone posted a way to determine the position of a short/open with
three measurements. 101 measurements has to be better!
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