[time-nuts] HP 5372A TIA Question

[Magnus Danielson]

Hi Adam,

On 05/30/2018 12:26 AM, Adam MacDonald wrote:
> Time Nuts,
> I have a nice new-to-me 5372A that I'd like to use as part of a DMTD stability analysis system.  After getting a few odd glitches from a very stable source spaced 2 ns above or below the main time interval reading,

OK, so the 5372A uses a 10811A as OCXO and then synthesize a 500 MHz
coarse clock which then runs in custom high-speed chips. The
interpolator is a delay-chain of DFFs.

So, if you jump +/- 2 ns it is that you most likely have an issue with
the start/stop and coarse-counting. Could also be that the interpolator
misses one way or another. Regardless I will ponder on it.

> I decided to run the performance verification checkout from the service manual.  The checkout calls for a BNC-T from the rear 10 MHz timebase output split to both A and B channels.  The spec is 100 ns +/- 200 ps but I am consistently getting either 101.6 or 101.4 ns in Time Interval mode on either channel.  So it seems to be high/off by exactly 1.4 ns.

Consider that you need to swap the cables to verify that it is static
with the setup and does not follow the cables. Also, there can be
trigger voltage offsets which may be the cause, so that may be due to
other reasons.

>  The standard dev is very low (typically 0-60 ps over several 100 point runs).  Curiously, in Continuous Time Interval mode, it reads dead on (100.0 ns).  I've run the sensitivity cal because I got the 160 error (dead battery), but not the interpolator cal (I don't have the appropriate riser card and the manual calls for a specific cable).  Has anyone seen this?  I suspect maybe the interpolator board needs to be ca
>  librated, but maybe something else?  Has anyone had experience trying to adjust the board without a riser?  Any other tests I might run to shed light on what might be causing this?

Let me ponder on this one. I don't think it is the interpolator boards,
sure they might need calibration, but that should not be the issue here,
you miss a cycle in the coarse counter on their the start or stop
channel. That should be the focus.

Cheers,
Magnus