[time-nuts] 8040c specification clarification, help for a time-nut beginner

[Tom Van Baak]

Welcome to the list. Congratulations on your masters effort. Which school?

There is no way the 8040c can make a claim about output accuracy without some assumption about the short- and long-term quality of the 1PPS reference input. They just mention "GPS" so your question is a good one. But it's reasonable to assume they mean a clean 1PPS from a good GPS receiver under ideal conditions, or other fuzzy words to that effect.

The other issue is that they don't mention over what interval the 1e-12 frequency accuracy is measured. Most GPSDO are accurate to 1e-12 or even 1e-13 over a day, but this does not mean it is accurate to that over any given minute or second. And to be picky, it that a one sigma accuracy spec or two or peak, etc.

How did you measure the 1PPS of the XLi-GPS? Also, how did you measure the ADEV of the 8040c?

Since this is for a masters, you can fully measure a 8040c without using GPS at all. Using your own reference (not GPS) just create a lab 1PPS with varying amounts of inaccuracy and see how well the 8040c tracks your reference. The resulting plot(s) would be wonderful and will show how well the 8040c disciplining works as a function of 1PPS accuracy, jitter, and wander. In this case, you don't have to fight any of the issues with an actual GPS receiver; that's a whole other can of worms.

/tvb

----- Original Message ----- 
From: "Pee Akka" <akkapee at gmail.com>
To: <time-nuts at febo.com>
Sent: Thursday, December 12, 2013 2:22 AM
Subject: [time-nuts] 8040c specification clarification,help for a time-nut beginner


> I'm currently doing my master's thesis on GPSDO devices. Nothing fancy but
> more than enough for a fledgling time-nutter. It seems that which ever
> direction I go with my master's, this place always pops up :)
> 
> I'm a bit uncertain about how to interpret one of the GPSDO's
> specifications. The device in question is a a 8040c Rubidium Frequency
> Standard with a SA.22C-LN oscillator (ie. the low noise version). The
> specification states that its frequency accuracy (ie frequency offset)
> after 20 minutes of 1PPS GPS-disciplining is <1E-12.
> 
> Do you think this specification the combined accuracy of the GPS receiver
> and 8040c device? In another words, if the 8040c is locked to GPS, is the
> whole receiver+8040c system's combined accuracy <1E-12? The GPS receiver
> that I have in use is XLi-GPS with +-30ns RMS 1PPS output.
> 
> The datasheet for 8040c is here:
> http://www.symmetricom.com/resources/download-library/documents/datasheets/8040c/
> 
> The measurements that I've done indicate that at least the frequency
> stability (ADEV) of the 8040c is between 9E-13 and 1E-12 from 1s to 1000s.
> 
> Thanks in advance.