I received one of Leo Bodnar's fantastic 100 pS pulse generators yesterday and spent most of today playing with it hooked up to my LeCroy DDA-125 which is a 1.5 GHz, 4 GSa/S 8 bit DSO.
As a consequence of some ill advised online purchases, I wound up with a considerable number of RF adaptors and 50 ohm terminators of dubious quality.
As an experiment I connected the pulser to a tee connected to the DSO BNC input set for 50 ohm DC coupling. I attached a ~ 2 ft 50 ohm cable with good quality connectors and tested the reflections from the 50 ohm terminators using a known good F-F BNC coupler. This resulted in 4 BNC terminators going into the reject bin.
By setting amplitude cursors at the peaks of the reflection from a good device I was able to screen a large number of adaptors as quickly as I could change them. I culled 11 more devices out of 60 or 70 that I tested.
VNAs commonly have software available to do TDR measurements by Fourier transform from frequency to time. In reflection seismology the recording system is typically evaluated by recording an impulse response. Before digital recording this was simply done as a system check. After the advent of digital recording it became common practice to zero phase the data using the impulse response of the instrument and the source to make interpretation of the data easier. This is usually accompanied by a Wiener filter to flatten the amplitude spectrum.
I've gotten rather interested in using a DSO and a fast pulse to do vector network analysis. Naturally this is limited to the BW of the DSO, but 100 MHz DSO's with deep memory are cheap. There is the issue of dynamic range, however, adroit DSP work can overcome that. And an Owon XDS2102A offers 12 bit ADC for $400.
I just bought an 8753B and 85046A in very nice shape. I also have a VNWA 3E and an xaVNA though I have not yet attempted to use any of them. So I have excellent instruments for verifying the results once I collect the various bits I still need to get.
My interest in using a fast pulse and DSO for vector network analysis is for the benefit of those who cannot afford such toys, but want to build HF gear. One of Leo's 100 pS pulsers is under $80 delivered to the US. The required software is fairly trivial, at least relative to what I'm used to dealing with. It requires retrieving data from the DSO, performing sums and FFTs and plotting.
I'm very familiar with the reflection seismology literature relevant to this, but not the EE literature. Does anyone know of any published work on using TDR for VNA? Historically fast pulses and sampling were very expensive. And even today, using TDR for VNA is not practical at UHF and above. My interest in prior work and literature is because when I write software I like to include the relevant citations in the comments. And I rather doubt that a ham building a QRP station would appreciate being dragged through reflection seismology.