TDR options for HP/Agilent VNAs - is it hardware or software?

[drkirkby]

I am looking to buy a used HP/Agilent VNA. My initial interst is in antennas, but expect to extend that to filters later.

A TDR is not high on my priority list, but it is something I can see I might want occasionally. I notice this is an optional extra for many HP/Agilent VNAs. Is this extra hardware fitted, or just software?

I can't help thinking that in principle at least, a time-domain response is just the FFT of the frequency domain response. So if I occasionally wanted the TDR facility, it would just be a case of writing a bit of software to do an FFT on the frequency spectrum.

Or am I missing something, and the TDR options give something worthwhile, that can't be done in software?

Dave

 

[biff44]

It is handy as it is almost real time TDR, whereas if you download the S2P files and do the computations offline it takes time and is a lot less useful! I believe the TDR option is purely in the software. They just turn it on with a software key.