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

[Magnus Danielson]

On 01/23/2013 03:48 PM, David Kirkby wrote:
> 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.

I really think he should use a TDR for that stuff. Besides, there is 
nothing very magic about the time domain option, it should be possible 
to cook the software yourself, but I suspect someone has already done 
it. My TDR would probably suffice, the actual measurements is done in 
minutes, need to work on the hard-copy details, but it is fairly easy to 
pull the data over RS-232 or GPIB.

Cheers,
Magnus