Bruce Griffiths wrote:
Joseph Gray wrote:
I have a borrowed HP 5328A with the Universal Module. I'm using
averaging mode and auto triggering. Counter does not have the OCXO
option. I'm using the internal oscillator, not locking to my GPSDO.
I was just messing around with a length of Belden 9273 and the 100 KHz
square wave output from my Spectracom distribution amp. Start signal
is the 100 KHz signal. Using a tee, the stop signal is the same 100
KHz after passing through the length of coax. I'm reading 18.9 ns. The
coax specs give a VOP of 66%. This should calculate out to a length of
3.74 M. When I measure the coax, I get 3.8 M.
I am including the BNC connectors in my length measurement. If I
subtract them, I'm much closer to my calculated length. Should the BNC
connector lengths be included or not? Or, is the measurement I'm
getting as good as it gets with this HP counter?
Joe Gray
W5JG
The measured delay includes the time offset between the start and stop
inputs.
This is unlikely to be zero, you need to measure it and subtract the
offset from the measured result.
Since the 5328A can only measure positive time intervals measuring
this offset is somewhat tricky to do.
Bruce
The simplest way of measuring the cable delay with the 5328A is to
measure the delay with a short length of cable between the start and
stop inputs and then increase the length of cable by connecting the
cable to be measured in series with the first cable measure the delay
again and subtract the first measurement from the second.
This procedure corrects for the start to stop offset as well as that of
the first cable.
Then the effects of finite rise time, trigger thresholds and reflections
should be considered.
One then has to consider the effects of the various connectors,
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