[time-nuts] Setting up PRS10 with M12+T GPS

[bg at lysator.liu.se]

>>The phase of the PPSOUT and the generated 10 MHz will probably not align
> up, >something which is critical to some applications.
> Yes, for example the DVB-T SFN requires the PPS and 10MHz phases to be
> aligned, better, not to move. This requires to slightly alter the 10MHz to
> keep the PPS aligned.
>
> Let me ask Bjorn: did you succeed in aligning the two PRS10?

Somewhat... I had a "stable" offset between the 10MHz PRS10 signals of
almost 8ns, moving +-2.5ns over some hours.

Moreover,
> what
> do you mean by "each other", a scheme like this:
>
>
>
> |-------------------------------------------------------------------|
> |                                                                   |
> |       PRS10A                        PRS10B           |
> |--->PPS IN PPS OUT------>PPS IN PPS OUT--|
>
>
> hoping that the font doesn't mess up the ASCII schematic...

Almost, I also let the PRS10A be steered by a Tbolt.

PLL settings 8 on PRS10A, and 0 on PRS10B, which should make PRS10B quick
enough to follow any wiggle the PRS10A do slowly following its Tbolt
supplied PPS_in.

I had

    locked Tbolt 1PPS going into PPS_IN of PRS10A
    PPS Out of PRS10A going into PPS_IN of PRS10B.

I watched/measured
    1) PPS out from Tbolt on ch 1  (yellow)
    2) 10MHz out from PRS10B on ch 2 (green)
    3) 10MHz out from PRS10A on ch 3 (blue)
    4) 1PPS out from PRS10 B on ch 4 (red)

see attached screendump from a 500MHz Scope.  I did not have enough time
to completely remove offsets between 10MHz signals from PRS10A & B. More
tuning should have been done on the PRS10A wrt the Tbolt PPS also.

Any comments?

--

   Björn

> On Wed, May 2, 2012 at 11:07 PM, Magnus Danielson <
> magnus at rubidium.dyndns.org> wrote:
>
>> Hi Azelio,
>>
>> On 05/02/2012 10:30 PM, Azelio Boriani wrote:
>>
>>> Magnus, you are correct but can I avoid to list our beloved
>>> counters/analyzers? The time-nut main tool is the TIC.
>>>
>>
>> Hehe, yes. But you can do great things even with a spare HP5335A for
>> instance. It's quite respectable with about 1 ns resolution in this
>> context.
>>
>> I have not tried using the SIA-3000 for TIC purposes. Just "getting
>> into"
>> the machine GPIB-wise is a bit of a challenge.
>>
>>  Anyway, to correct the PPS input for the PRS10 the hardware approach is
>> a
>>> must: so a delay line and a microprocessor are needed. Unless the SRS
>>> can
>>> develop a suitable software for the PRS10 (an inverted TTL serial line
>>> is
>>> already present) to read the M12+.
>>>
>>
>> Well, look at the Spectratime SRO-100, which already has that feature.
>>
>> http://www.spectratime.com/products/isync/gps-disciplined/SRO-100
>>
>> Architecture-wise it is very similar to the FEI 5680, a 60 MHz VCXO, DDS
>> for FLL and then DDS for output. PPS input and output makes you think
>> about
>> PRS-10. The PPS input has about 1 ns resolution.
>>
>> Now, there is a few things which differs from the PRS-10. It move it's
>> internal (and later also its output) PPS to align up to the PPS
>> reference.
>> It hence does not need an output alignment. This makes the 7,5 MHz clock
>> (133 ns cycle) less critical. BTW I do the same in my products. The
>> phase
>> of the PPSOUT and the generated 10 MHz will probably not align up,
>> something which is critical to some applications.
>>
>> Also, it can take info from Jupiter-T, OnCore, M12+ and SuperStar II
>> receivers for detailed timing info.
>>
>> Cheers,
>> Magnus
>>
>>
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