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

Brooke Clarke brooke at pacific.net
Thu Dec 12 14:48:50 EST 2013


Hi Pee:

Here's some vocabulary to help you.

The 8040c is a frequency standard, not a GPSDO.  That's to say it doesn't have a GPS receiver built in, but instead 
requires an external 1 PPS input.
It's very similar to the Stanford Research PRS-10 in that respect.
http://www.prc68.com/I/PRS10.shtml

The Thunderbolt is a combined GPS receiver and disciplined oscillator.
http://www.prc68.com/I/ThunderBolt.shtml
It's input is from a GPS antenna.  Outputs are 1PPS and 10 MHz.

The <1E-12 frequency accuracy after 20 minutes is not a specification, but rather a "performance parameter".
That may be because it may depend on the quality of the 1 PPS input.
Note the Allan deviation at 1 second is not as good.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

Pee Akka wrote:
> 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.
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