[time-nuts] Basic TIC measurement

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Oct 7 05:46:49 UTC 2009


Joseph Gray wrote:
>> Did you use a resistive splitter or just a tee to split the signal?
> Just a tee. I have tees and terminators at each input of the 5315A as well.
You need to use a resistive splitter and not a tee to control reflections.
If you don't have one, make one using 3 resistors mounted in ametal box
with a coax connector for each arm/port of the splitter
This will work reasonably well if your signal risetimes aren't too short
ahnd the component leads arent excessively long.
If the 2 cables attached to the tee have the same length you are
attempting to drive a 25 ohm load from the source attached to the other
arm of the the tee.
If the cable delays are mismatched the impedance seen at the tee will be
more complex.
> I guess I could try using the multiple outputs on the back of the
> Spectracom 8140, but that would introduce another variable -- the
> outputs may not be exactly in phase. Also, isn't a pulse or square
> wave better for doing TI measurements? What the heck. I may try that
> just to see what happens :-)
You may as well just do it to see what happens, but don't expect much
better performance.
>> Either estimate it (use a circuit simulator) from the input impedance (R
>> and C) and the signal transition times or find a TDR (expensive) to
>> measure it.
> Well, actually I can borrow a TDR. I'll have to read up on how to
> measure reflection coefficient with it. The only time I ever used a
> TDR was many years ago, in the Air Force.
> Joe Gray
It is instructive to vary the TDR transition time and watch the
amplitude of any reflections reduce as the risetime increases.


More information about the time-nuts mailing list