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

[Bob kb8tq]

Hi

One term you keep tossing up is “nominal phase coherence”. Typical GPS will do “phase coherence” 
at the 10 ns level to a fairly high degree of confidence (90 something percent) with a number of 
footnotes. You have never mentioned what your requirement is so it’s a bit tough to know what
you are up against. If you are trying for “a couple of degrees at L band” from 0.1 second on out, 
GPS simply isn’t going to do that, no matter what you do. 

Bob

> On May 30, 2019, at 1:58 PM, life speed via time-nuts <time-nuts at lists.febo.com> wrote:
> 
>   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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