[time-nuts] Basic TIC measurement

Joseph Gray jgray at zianet.com
Wed Oct 7 04:02:29 UTC 2009

Bruce, thanks for the very helpful advice. My comments are interspersed below.

> You need to measure this delay.
> Split the signal in 2 and feed it to both inputs with nominally equal
> length cables.
> Measure the difference then swap the 2 cables over and measure the
> difference.
> Average the 2 differences to get the interchannel differential delay.
> This fails if the counter cant measure negative delays and a more
> complex procedure is required.

I get 0.9nS one way and 1.1nS with cables swapped. This with tees and
terminators on each input. The cables are almost exactly the same
length. So, I have a 1nS difference between the two inputs.

> Another issue is if the slew rate of the signal at the trigger threshold
> is low then trigger threshold offsets between the 2 counter inputs will
> affect the effective differential delay between the 2 inputs.

I tried it both in trigger mode and in level mode, where the trigger
threshold is supposed to be at zero crossing (according to the
manual). The difference between the two is about 0.1nS, which may be
due to my inaccurate setting of the trigger controls.

> However you need to ensure that the reflection coefficient of each 5315
> input is small.

How do I do this?

Thanks very much,

Joe Gray

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