That's the Raleigh criterion for separating two events. I was referring to identifying the location of a discontinuity. Very different problems.
I've viewed the TDR aspect as "Where is the bad spot in my cable?" and "Where is the impedance discontinuity in my PCB trace?"
Once you want to look at the reflection from the the SMA side of an SMA to N connector separately from the N side, you have to have 20 GHz or more BW. And even at 20 GHz in the time domain, it's not easy. I've been doing a lot of it testing RF connectors using a Tek 11801 & SD-24.
However, I'm fairly certain that, if you have a well defined problem such as the mismatch at either end of an SMA to N adapter, you can solve the problem of the timing to better than the Rayleigh criterion using basis pursuit. However, doing this would require mastering the ugliest and most complex math I ever came across in my life. It's simple to do in practice, but the logic of how and why it works is painful. David Donoho has a proof of a single theorem which takes 15 pages!
I'd like to note that I have serious technical issues with that application note. It poses a lot of "problems" which are trivial to solve, but presented as proprietary to HPAK despite being sufficiently well known to be basic DSP 101 examples and homework. I've not read all of it, but much of it is in Dunsmore's book which I *have* studied very closely. At present I don't know if the issue is terminology and notational conventions, substantive errors or marketing FUD. While the reflection seismology community has been doing DSP for 20 years longer than the EE community, the EE community chose not use the mathematics community lexicon adopted in geophysics. Same words, but *very* different meanings. Having worked in several seismic processing shops, my experience is that it takes about 6 months to map the words people use at lunch to the correct equations. If it's that difficult in geophysics, going between that and electronics engineering is *much* worse.
In sum, this quickly turns into a major communications problem. I've seen a lot of arguments which amounted to nothing more than different meanings for the same words.
Have Fun!
Reg