[time-nuts] Next upgrade

Bob kb8tq kb8tq at n1k.org
Thu Nov 23 08:09:32 EST 2017


Hi

Yes, the “has no GPS” box becomes the active device in a REF0 / REF1 pair. 
If a survey is involved, it can take a *long* time for things to sort out.

Bob

> On Nov 23, 2017, at 7:22 AM, Adrian Godwin <artgodwin at gmail.com> wrote:
> 
> Turns out is does work - Initially, when I linked them, both boxes had the
> standby light go out and the unmodified ref-0 (with no GPS receiver) showed
> Fault and No GPS.
> 
> So I assumed there was some problem that might be causing them to conflict
> over the interface, and unplugged it.
> 
> I've tried it again with more patience and after 10 minutes or so, the
> modified ref0 goes into standby and the one without a receiver has only the
> green ON light.  I guess that's working correctly :)
> 
> 
> 
> On Thu, Nov 23, 2017 at 12:23 AM, Jerry Hancock <jerry at hanler.com> wrote:
> 
>> Adrian, when you stated it didn’t work, what were the results?
>> 
>> I had mine running in HA mode, if you can call it that, because only one
>> has a GPS.  Actually now that I think about it, the separate but modified
>> REF0 and modified REF1, assuming separate power and antennas, is probably
>> closer to HA than the original application.  I have both mine running now
>> with Lady Heather tracking each and I’ve been playing around with
>> comparisons.  Now in my case, if either goes down for any reason the other
>> can take over.  I guess in order to make them truly HA, we would need a
>> diode or relay switched transfer to the active unit.
>> 
>> Jerry
>> 
>>> On Nov 22, 2017, at 4:10 PM, Adrian Godwin <artgodwin at gmail.com> wrote:
>>> 
>>> Yes, I cross-connected  the pins, but I didn't cut any short.
>>> 
>>> 
>>> 
>>> On Wed, Nov 22, 2017 at 11:36 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>>> 
>>>> Hi
>>>> 
>>>> I have run a number of the REF0 / REF1 combos. They all seem to work
>> fine.
>>>> The standard cable has some odd short pins on it. If you are not hot
>>>> plugging
>>>> the cable I don’t think they matter at all. If anything, the system is
>>>> more reliable
>>>> with a normal length pin on the connector.
>>>> 
>>>> Bob
>>>> 
>>>>> On Nov 22, 2017, at 6:08 PM, Adrian Godwin <artgodwin at gmail.com>
>> wrote:
>>>>> 
>>>>> I've got several of the Ref 0 boxes but none of the Ref 1. I've added
>> an
>>>>> Oncore GPS receiver to one of them as per Peter Garde's notes and it
>>>> works
>>>>> well.
>>>>> 
>>>>> But I'd like it to run with an unmodified Ref 0 too in the ref0/ref1
>>>>> configuration. Not that I need an HA reference but just for interest.
>>>> I've
>>>>> only had a quick look so far and found that connecting the two together
>>>>> with a 15-pin cable didn't work.
>>>>> 
>>>>> Has anyone looked into this ?
>>>>> 
>>>>> 
>>>>> On Wed, Nov 22, 2017 at 11:01 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>>>>> 
>>>>>> Hi
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>>> On Nov 22, 2017, at 5:16 PM, Jerry Hancock <jerry at hanler.com> wrote:
>>>>>>> 
>>>>>>> Three questions:
>>>>>>> 
>>>>>>> 1) Now that I’ve split my Lucent RFTG-U into a REF0 and REF1 unit
>> with
>>>>>> both supplying 10Mhz and 1PPS, is there a way to combine the outputs
>> or
>>>>>> some other technique to improve the short and/or long term
>> performance?
>>>>>> 
>>>>>> You can monitor one against the other. Ideally you would want three
>>>>>> GPSDO’s and a
>>>>>> monitoring setup. That way you can figure out which of the three has
>>>> gone
>>>>>> bad.
>>>>>> 
>>>>>>> 
>>>>>>> 2) I’ve become interested in Rubidium Disciplined Oscillators
>> recently
>>>>>> and was now thinking of purchasing one of the PRS-10 that I see on
>>>> Ebay. If
>>>>>> I did that and replaced one of the DOCXOs from one of the Lucent
>> boxes,
>>>>>> what impact would this have on the overall performance both with and
>>>>>> without (when in hold-over)?
>>>>>> 
>>>>>> If you go into holdover, you are the exception. Most setups rarely go
>>>> into
>>>>>> holdover. When they
>>>>>> do, it’s because a hurricane just went over the house. Generally
>> that’s
>>>>>> not when the focus is going
>>>>>> to be on timing experiments.
>>>>>> 
>>>>>>> Basically, is it worth the money to upgrade one of the boxes to a
>>>>>> Rubidium disciplined oscillator assuming the GPS signal is rarely
>> lost?
>>>>>> 
>>>>>> Not worth the money if you are only looking at holdover and have a
>>>> typical
>>>>>> setup.
>>>>>> 
>>>>>>> 
>>>>>>> 3) Figuring the PRS-10 will cost around $250 when all is said and
>> done,
>>>>>> is there a better option to improve my GPSDO system?
>>>>>> 
>>>>>> 
>>>>>> Disciplining implies continuously correcting. Rb standards age much
>> less
>>>>>> than a typical
>>>>>> OCXO. Oddly enough their temperature stability may not be as good as a
>>>>>> high end
>>>>>> DOCXO. It is fairly common to try to stabilize the environment your
>>>>>> standards operate in.
>>>>>> To the extent you are successful this reduces the need to deal with
>>>>>> temperature.
>>>>>> 
>>>>>> The net effect is that disciplining an Rb at a rate (filter / control
>>>> loop
>>>>>> / manual tweak) of less than
>>>>>> a few days actually makes the Rb worse. Coming up with software to
>> “back
>>>>>> off” on the tuning is
>>>>>> not as simple as it might seem.
>>>>>> 
>>>>>> This comes back to the fact that the GPS signal (or any of the sat
>>>>>> signals) are quite noisy. You
>>>>>> need to average them over a *long* time to get good performance. Rb’s
>>>> are
>>>>>> enough better than
>>>>>> a GPSDO OCXO that the time ranges really stretch out ….
>>>>>> 
>>>>>>> 
>>>>>>> I basically use the GPSDO as a reference for any equipment that takes
>>>> an
>>>>>> input. I have no monetary need for a reference, just an interest.
>>>>>> 
>>>>>> For most normal test equipment, a GPSDO output is “plenty good
>> enough”.
>>>> As
>>>>>> a source for fancy
>>>>>> timing experiments … maybe not so much. As a phase noise reference or
>> a
>>>>>> spur free source for
>>>>>> microwave games … also not the best way to go.
>>>>>> 
>>>>>> Bob
>>>>>> 
>>>>>> 
>>>>>>> 
>>>>>>> Thanks.
>>>>>>> 
>>>>>>> Jerry
>>>>>>> 
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