[time-nuts] Common sky pps errors for any GPSDOs?

Matt Ettus boyscout at gmail.com
Mon Jan 5 22:28:11 UTC 2009


On Mon, Jan 5, 2009 at 12:13 PM, Lux, James P <james.p.lux at jpl.nasa.gov> wrote:
>
>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com
>> [mailto:time-nuts-bounces at febo.com] On Behalf Of Matt Ettus
>> Sent: Monday, January 05, 2009 11:31 AM
>> To: Discussion of precise time and frequency measurement
>> Subject: [time-nuts] Common sky pps errors for any GPSDOs?
>>
>> I am working with someone who needs to have time synchronized
>> reception of signals in various locations which are separated
>> by less than 100 km.  This is a situation similar to VLBI,
>> but since the distances are shorter, the center frequencies
>> are lower, and the integration times are much shorter, we
>> probably don't need a Hydrogen Maser, and the application
>> can't afford one.
>>
>> The real question is whether we can get away with a GPS
>> disciplined OCXO or whether we would need to use a Rubidium.
>> Does anyone have any data on the relative frequency and/or
>> phase errors of the 10 MHz reference out, and relative PPS
>> time errors of any commonly available GPSDOs?
>
> Isn't that just the Allan Deviation data? Symmetricom has datasheets on their website for their various modules. They have a GPS discplined quartz oscillator in several flavors.
> http://www.symmetricom.com/media/files/downloads/product-datasheets/ds%20XLi%20Options%202.pdf


I don't think Allan Deviation is the right measure.  First, standard
Allan dev numbers won't take environmental differences into account.
Also, isn't Allan Dev measured vs. a better reference?


> Something else to consider is doing post processing.. Use a nice quiet 10MHz oscillator for your source/sampling clock, and record the 1PPS from the GPS receiver as well as your unknown, then figure out after the fact what the oscillator was doing.


Unfortunately, post processing isn't possible in this app, since it is
a real-time communications application.

Thanks,
Matt




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