[time-nuts] GPS 1PPS, phase lock vs frequency lock, design (Bob kb8tq)

[life speed]

  2. Re: GPS 1PPS, phase lock vs frequency lock, design (Bob kb8tq) 

Hi

The TBolt is a very unique design. It directly uses code phase information 
against the OCXO. The net result is really no different than the “correction
message” approach, but it is a different implementation. Since you can’t 
*buy* the guts of a TBolt to strap into a DIY GPSDO, it’s not generally part
of a “I want to build a GPSDO from scratch” conversation.

Bob

> On May 29, 2019, at 9:50 AM, Alberto di Bene <dibene at usa.net> wrote:
> 
> On 2019-05-29 14:53, Attila Kinali wrote:
>> The saw-tooth correction is the error of the PPS signal, as generated by
>> the hardware, and where it really should be. The clocks of most GPS receivers
>> are in the order of 20-60MHz and are usually unsteered TCXOs (or even XO for
>> the cheap ones). Hence the granularity at which the PPS can be generated
>> is fixed. The saw-tooth correction gives you a higher accuracy (or removes
>> noise) from what you would get without.
> 
> Am I correct if I suppose that the Trimble Thunderbolt, which uses the 10MHz OCXO as clock for the processor, does not need any saw-tooth correction ?
> 
> TNX
> 
> 73  Alberto  I2PHD
> /<<< http://www.weaksignals.com >>>/
Just to be clear, I am an electrical engineer working on a commercial new product design, which already has a high-performance 10MHz OCXO as part of the product.  Although I realize much of this list is composed of DIY and hobbyists, it has always been clear to me there are some smart people participating in these discussions.  I am in the investigation phase of a feature enhancement to the product that is unfamiliar to me, hence my questions.
Bob,
Would you care to elaborate on "directly uses code phase information against the OCXO"?
I have noticed that a product my company is currently manufacturing uses a "GPS receiver" containing a TCXO, which we then use the 1PPS to discipline a low-end 100MHz OCXO.  When I investigated the performance of our current design it did not meet my requirement of nominal phase coherence of two separate receivers.
It would seem that a GPS receiver containing an oscillator may not make sense for a design that already contains a high-end 10MHz OCXO, rather the implementation should use the oscillator that is already part of the design.
Lifespeed

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