[time-nuts] GPSDO Component Selection

[bg at lysator.liu.se]

Chris,

> On Sun, Sep 9, 2012 at 6:18 AM, Don Oconnor <eGunk at wowway.com> wrote:
>> Hello,
>>
>>
>>
>> I would like to design and build a microcontroller based GPSDO. And I
>> have a couple of questions some of you may be able to answer.
>>
>>
>>
>>
>>
>> 1.         I am going to use Trimble SMT GPS timing module but I'm
>> curious. Does a GPS timing receiver produce a more precise 1 PPS output
>> than a standard GPS tracking receiver in a static location? Or does it
>> just produce a 1 PPS signal that is more accurate to GPS time?
>
> Both of the above by several orders of magnitude.  The best timing
> mode GPSes today have the PPS within a few tens of nanoseconds of UTC
> (one sigma) while the typical navigation mode GPS has the PPS within a
> few microseconds.   Also the timing mode GPS can do things like a self
> survey to determine location.  The finding a soltion for time within
> _knows_ it is not moving removes some uncertainty in the result.   I'd
> say it would be almost pointless to use a nav receiver in a GPSDO
> especially when decent timming mode receivers sell for under $20.

True for a cheap oem navigation receiver. Not true for a geodetic quality
receiver, who usually have some options (external frequency input, PPS_in)
to make them the best timing receivers available. However they are much
more expensive than the typical single frequency timing reciver.

Look at:

     http://www.septentrio.com/products/receivers/polarx4-tr-pro

     http://www.topconpositioning.com/products/networks/network-systems/net-g3a

     http://www.novatel.com/solutions/timing/#whatWeOffer

     http://javad.com/downloads/javadgnss/sheets/Delta-G3T_Datasheet.pdf

     http://javad.com/downloads/javadgnss/how-to/hardware/Receiver_Clock_Synchronizing_Configuration_Example.pdf

--

   Björn