[TowerTalk] FA-VA5 question

[Michael Tope]

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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