[time-nuts] T.I. experimenting - newbie question

[J. Forster]

Seems like you are asking where the "reference plane" of a BNC is. The
distance between the reference planes defines the electrical length of a
cable or adapter or "L" or "T".

Unlike "precision" connectors like the APC-7 or GR 900, the reference
plane of a BNC is not well defined. A quick Google turned up nothing
really useful.

So, at a guess, if you look at a female BNC, the Teflon surrounding the
center conductor is flush with the end of the cut off end of that
conductor. This is about 0.0" to 0.2" below the end of the outside
conductor. My GUESS is that cut off end is the reference plane. This
corresponds to the bottom of the annular well in the male VNC.

You might be able to find more info by researching VNAs or TDRs, Remember,
a BNC is not a precision connector.

Best,

-John

==================



> 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
>
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