[time-nuts] Data collection from 5115A phase noise test set?

[Anders Wallin]

Hi all,

A 5115A phase noise test set landed in our lab and I am wondering about the
data collection.
It has two telnet ports one for commands and one for phase data.
When issuing "start" on the command-port it starts spitting out
phase-difference values on the data port.

However it seems to me that the phase data alone (REF-DUT phase, in units
of the REF period) is almost useless without knowing the internal workings
of the device.
The phase values are clearly not the true phase difference, which would
quickly accumulate to a huge number with e.g. REF=10MHz and DUT=11MHz. My
understanding is that digital downconversion (DDC) is performed on both REF
and DUT signals, and without knowing the LO frequencies for the DDC the raw
phase data alone is almost useless.

The command prompt does have commands for displaying the internally
calculated ADEV, L(f), frequency-counter readings, etc. and these seem to
show correct and OK values, but there seems to be no way to reproduce e.g.
the ADEV or frequency-counter values/statistics from the raw phase values
on the data port??
Is this correct? Any other experiences with the 5115A or higher end 5120A?

thanks,
Anders