[time-nuts] Help needed with frequency standard

[Bob kb8tq]

Hi

> On Sep 29, 2020, at 10:23 PM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> Mark:
> 
> I don't have a PPS syncable PRS-10 yet, but will probably be getting one
> within a
> year or so.  My expectations are not great, however, because I already know
> that
> the received GPS time has diurnal wiggles to the tune of up to 10's of nsec
> p-p.
> And I also know that the PRS-10 (and probably all others in its price
> class) make
> seemingly random frequency "adjustments" on a time scale of just a few
> hours.
> For a GPS disciplining loop to fix both, it would have to have a loop time
> constant
> long compared to a day on the one hand, yet a loop time constant of well
> under a
> day on the other.  It's kind of tough to have one loop with both properties
> at once.
> 
> Dana


Rb’s do not have super duper performance at short tau. At least not compared to
reasonably good OCXO’s. An OCXO with a 1 second ADEV below 1x10^-12 is
not terribly hard to find. Your “typical” Rb ( = not a 5065) is going to be 10X worse
than that at 1 second. Indeed the PRS-10 (by design) has some interesting issues
in the 1 to 10 second region ( = it is worse than several others out there …). 

If you are looking for good short term, an OCXO is cheaper to buy and cheaper
to run ( = lower power ). What you are after very much dictates what makes sense.
There is no “one size fits all” solution.

A fancy Rb GPSDO will have some method of stretching the disciplining process out
*way* past what anb OCXO based part would do. Some way of looking at day to day
(or couple day) readings is needed. It still will not take out all of the daily “wobble” in
GPS, but it will attenuate it some. 

Indeed an L1 / L2 based part ( possibly using a ZED-F9P (or T) ) could take out all
the wobble if corrections are applied. That’s not as crazy a thing as it once was. There
would be a bit of lag to deal with so it’s not quite a slam dunk. 

Since Rb’s do not typically have super temperature performance ( = they are not
a Cs standard …) some sort of solution also needs to be applied in that area if
you will be running a really long loop. Otherwise all you will do is track your
HVAC system :)

Fun !!

Bob



> 
> 
> On Tue, Sep 29, 2020 at 1:22 PM Mark Spencer <mark at alignedsolutions.com>
> wrote:
> 
>> I would be curious to hear from those who have a GPS disciplined PRS 10 in
>> their home time labs.   I was never that impressed with the performance of
>> one of mine in that configuration from a 10 MHz ADEV perspective (I did try
>> making a few parameter changes.) I ended up essentially free running mine
>> but would occasionally apply a 1pps signal to mine as means of adjusting
>> its output frequency on an as needed basis.
>> 
>> I may try this again with a different PRS10 (the 1pps output on the unit
>> in question failed a few years ago but I have a spare that has been
>> recently put into service.)   Perhaps the second unit will work better.
>> Both units were obtained via the usual auction site.
>> 
>> Mark Spencer
>> mark at alignedsolutions.com
>> 604 762 4099
>> 
>>> On Sep 29, 2020, at 8:02 AM, Luiz Alberto Saba <las at intercat.com.br>
>> wrote:
>>> 
>>> Hi guys
>>> 
>>> 
>>> I want a stable & reliable frequency standard.
>>> 
>>> I do NOT have a cesium beam.
>>> 
>>> I DO have a lot of gpsdos and some rubidiums.
>>> 
>>> Since I have one PRS-10 and this device has a 1 pps input, you already
>> know what I'm thinking...
>>> 
>>> What I have:
>>> 
>>> Trimble Thunderbolt
>>> 
>>> Trimble UCCM
>>> 
>>> Symmetricom UCCM
>>> 
>>> Samsung UCCM
>>> 
>>> HP 58503A
>>> 
>>> TruePosition
>>> 
>>> Oscilloquartz Star 4+
>>> 
>>> and a little board with a ublox LEA 5T and 1 pps output.
>>> 
>>> Which device is more suitable for disciplining the PRS-10?
>>> 
>>> My gps antenna setup is:
>>> 
>>> Symmetricom 58532A on the top of the water tank of my building with a
>> very good sky view.
>>> 
>>> A Raven Industries LA-21-1575-100-T. About 50 m of RG6.
>>> 
>>> A Symmetricom antenna distributor (don't remember the code but is the 4
>> outputs one)
>>> 
>>> By the way... Someone knows the delay of the inline amplifier and the
>> antenna distributor? (for Lady Heather)
>>> 
>>> Mark Sims is out there reading this list? I'm having problems with LH
>> 6.14 and the UCCM units.
>>> 
>>> Any help you can give me will be welcomed.
>>> 
>>> 
>>> Thanks
>>> 
>>> 
>>> Luiz Alberto Saba
>>> 
>>> from Santos - São Paulo - Brazil
>>> 
>>> 
>>> 
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