[time-nuts] Is there any way to use a TIC to measure time of reflection on a PCB?

[David Kirkby]

There's a fairly interesting (to me at least), discussion on an
Agilent forum devoted to the calibration of vector network analyzers.

http://www.home.agilent.com/owc_discussions/thread.jspa?threadID=34809&tstart=0

The title of the thread is "Coefficients of fringing capacitance polynomial"

A student needs to find the open-circuit fringing capacitance of a
piece of microstrip line. For this he needs to know the time between
the reference plane of the SMA connector and the open circuit
microstrip.

An obvious way to do this is with a vector network analyzer with a
time-domain option. In HP/Agilent VNAs, this is option 010. The
student has access to an obsolete and unsuported HP 8753C 6 GHz VNA,
but it does not have the time-domain option.

I thought he might be able to convince someone at Agilent to give the
uni this option, which is just enabled by software. So far that has
not worked. I did offer to help with access to my HP 8720D VNA which
has the time-domain option.

But more to the point, one of Agilent's VNA gurus, Dr. Joel Dunsmore,
the author of this book

http://www.amazon.co.uk/Handbook-Microwave-Component-Measurements-Techniques/dp/1119979552

has said the time domain resolution would not be sufficent on a 6 GHz
VNA for this - he would need a resolution of around 100 ps, which
would need a 20 GHz VNA. My HP 8720D VNA is a 20 GHz model, but I
don't have a calibration kit for greater than 9 GHz.

I was just wondering if there was any way a time-interval counter
could help.I can't think of a way, and I'm 95% sure there is not a
way, but a TIC would offer the timing resolution better than is
achievable with a 6 GHz VNA. I suspect one would need a directional
coupler to look at the reflected wave, and there is no way to correct
for systematic errors like there is with a VNA.

If I had an HP or Agilent 85052B Standard Mechanical Calibration Kit,
(DC to 26.5), then my VNA would just about have enough time-domain
resolution, but I don't have such a cal kit, and they are not exactly
cheap, even on eBay.

Dave