[time-nuts] Extended length Phase Noise Measurements with TimeLab

[John Miles]

As JohnA says there's no hard limit on the duration for phase data logging,
other than available RAM.  She would definitely want to use a 64-bit PC for
this.  The TSC 5120A cranks out phase data at 1000 samples per second by
default, so even a well-endowed 64 bit PC will run out of memory when trying
to record for >> 1 day.  Two things you can do about that:

- Use the 'set phaserate' command over a Telnet connection to lower the data
rate from the 5120A to 10 or 100 samples per second.  Change the 'Input Data
Rate' field in the TimeLab acquisition dialog accordingly.  This will work
only with newer 5120A firmware.

- Leave the TSC's phase data rate (and the Input Data Rate field) at 1000
samples/second and use the Output Decimation field to reduce the amount of
stored data.  

Both of those options should be used with TimeLab 1.1 or greater.  

For the issue where the 5120A stops the measurement, I'd log the signal with
a counter or a scope, maybe, to make sure that the signal isn't going even
farther out of range than expected.  If so, it would be best to fix that
problem at the source.  Otherwise, consider using a bandpass filter or PLL
whose bandwidth is wide enough to accommodate the desired analysis spectrum
but narrow enough to act as a flywheel during the (hopefully brief)
excursions that are confusing the 5120A. 

-- john, KE5FX
Miles Design LLC


> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Tom Knox
> Sent: Friday, May 03, 2013 11:22 AM
> To: Time-Nuts
> Subject: [time-nuts] Extended length Phase Noise Measurements with TimeLab
> 
> Recently I was looking at a co-workers Lab View measurements taken with a
> 5120A. She is studying vibration on Phase Noise. I asked how Lab View
> compared to TimeLab and she said in many ways she prefers TimeLab but ran
> into a problem. The research she is currently conducting requires
collecting
> data in extremely long measurement periods beyond the TimeLab limits. Is
she
> missing something? If not is measurement length an easy fix? One other
> problem during her project was related to the 5120A, occasionally the
vibration
> must hit a resonance and the 5120A stops measurement saying measurement
> parameters were exceeded. It would be nice to be able to adjust or disable
that
> feature. Thanks in advance for your ideas.
> 
> Thomas Knox
>