[time-nuts] Lost GPS lock or 1PPS recently?

Bob kb8tq kb8tq at n1k.org
Fri Sep 7 20:31:32 EDT 2018


Hi

This is Time Nuts, not end of the world nuts …..

I most certainly did *not* design these systems. The *do* have timing requirements. If those requirements 
are not met, they stop working. That’s just the way it goes. Designing these systems at the timing level was
done a decade ago. You can object to what they did, it’s about ten years to late to change anything. Tight timing
gives then more capacity … tough to argue with even if you weren’t to late. 

If *you* believe there is an alternative system now in existence that will supply the timing these systems require … 
that *is* a Time Nuts topic. So, let’s hear about the numbers on the system you believe will supply what’s needed.
I think we’ve all heard plenty of “the world is ending” stuff. 

Bob

> On Sep 7, 2018, at 7:01 PM, Scott McGrath <scmcgrath at gmail.com> wrote:
> 
> You are SO convinced that GPS will ALWAYS be there,   I’m NOT (Think Carrington Event) and i’ve been part of a few disaster exercises where both Internet and GPS were considered ‘down’ for the exercise and these exercises are done in conjunction with the military so PPS was also ‘off the table’.
> 
> It was quite an eye opener to see how many networks could not keep time synchronized within 5 minutes much less 5 seconds because of the cheap XO’s used in servers and workstations(NTP will ALWAYS BE AVAILABLE).  Just like the old Sun workstations.
> 
> It was also fun watching the multimillion dollar Harris radios drift once they no longer had a 10 Mhz input from a GPSDO.   One would think the local timebase would be a bit better than it was.  
> 
> The older ‘Pacer Bounce’ and Falcon series radios did much better because they had good local timebases and made no assumptions of the availability of a external timebase.  Whereas the new radios depend upon it.
> 
> These exercises are intended to practice restoring government communications after a large scale natural disaster.    And without readily available precision time it aint easy.
> 
> Its also fun watching executives realizing that their phone during the exercise is a paperweight useful only in weighting down stacks of Form 213’s
> 
> Its not for nothing that Symmetricom is building more 5071’s than HP/Agilent ever did.
> 
> On Sep 7, 2018, at 5:18 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
> 
> Hi
> 
> You are not trying to run a cell system when checking your local oscillator against LORAN.
> It’s two completely different things. The timing requirements of the modern systems are indeed
> way past what LORAN can deliver. We’re not talking about 1970’s state of the art anymore. You
> need a time source that is in the 10 ns range to keep this stuff running. Multiple microseconds of 
> error in your timing source aren’t good enough for what they have up and are rolling out.  Full 
> end of holdover spec on many of them is below 2 microseconds. Normal operation is under 100 ns.
> Give the cell outfits another couple years and that’s all they will have on the air.
> 
> 
> Bob
> 
>> On Sep 6, 2018, at 9:08 PM, Scott McGrath <scmcgrath at gmail.com> wrote:
>> 
>> 
>> As to eLORAN,  you can deny positioning but maintain timing service simply by modifying the GRI and since eLORAN is software based thats not a difficult change.
>> 
>> Navigation receivers go into fail but timing receivers only need ONE station.   As the users of SRS700’s and Austrons do when Wildwood is active.
>> 
>> With GNSS its a hell of a lot harder and without SA your only option is to turn off all the C/A signals hence denying civillian use of GNSS
>> 
>> I’m pretty sure if a non-state actor was doing weaponized drone attacks with GPS for guidance,  GPS for civilian use would be shut down in a NY minute .
>> 
>> Remember govt users would not be affected as they have access to the PPS and the ‘word of the day’ to make it active.
>> 
>> You dont need conspiracies to think of conditions where GPS would be shut down for long periods of time and where reasonable people would agree with the shutdown.
>> 
>> On Sep 6, 2018, at 8:44 PM, Scott McGrath <scmcgrath at gmail.com> wrote:
>> 
>> Gee,  thats strange especially for those of us who ran the Austron comparitors to check our local standards against the LORSTA’s
>> 
>> 
>> 
>> On Sep 6, 2018, at 8:04 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>> 
>> Hi
>> 
>> No, eLoran *never* on it’s best day could ever deliver the kind of timing that the vast majority
>> of these systems require. It simply is not and can not do the job. The world has moved *way*
>> past the sort of timing it can actually deliver. 
>> 
>> Bob
>> 
>>> On Sep 6, 2018, at 6:35 PM, Scott McGrath <scmcgrath at gmail.com> wrote:
>>> 
>>> Actually we DID have a radio based system that provided sufficient accuracy it was called eLORAN but it was killed by US politicians because they did not want a much more inexpensive to operate system ‘competing’ with GPS.    Shutting down LORAN saved 32m dollars annually the NAVSTAR GPS program costs billions annually.
>>> 
>>> Ironically while LORAN’s absolute accuracy is less than GPS,  repeatability was much better so fishermen liked LORAN better.
>>> 
>>> Once again the empty suits won and the navigation and timing community lost.
>>> 
>>> Wrt cellsites staying operational i imagine the oscillators in holdover would probably remain sufficiently synchronized for a month or so.
>>> 
>>> 
>>> 
>>> On Sep 6, 2018, at 4:56 PM, Bob kb8tq <kb8tq at n1k.org> wrote:
>>> 
>>> Hi
>>> 
>>> Well, we *do* have experience with that. It was called selective availability. Indeed it might get turned back on again. It’s impact on a properly designed GPSDO - not much. It takes a bit longer to get to best stability. System time wise, it still works “good enough”. 
>>> 
>>> A four hour long test format also does basically nothing to a GPSDO based system. You didn’t read anything in the papers about all cell service in three states going away. The devices did what they are supposed to do and everything did it’s boringly normal thing ….. it worked fine. 
>>> 
>>> I still don’t quite understand just what people think could replace satellite based timing in these systems. None of the “radio based” systems are within a factor many thousands to a few million of being adequate. 
>>> 
>>> =====
>>> 
>>> Now, if this is headed off into a “the government is coming to break down the doors and take away all my toys sort of thing. That’s very much *not* a Time Nuts topic.
>>> 
>>> Bob
>>> 
>>>> On Sep 6, 2018, at 11:34 AM, Scott McGrath <scmcgrath at gmail.com> wrote:
>>>> 
>>>> And there is the other significant vulnerability since GPS is a MILITARY system the DoD can take it offline for any reason at any time.  
>>>> 
>>>> Leaving civilian users with nothing, 
>>>> 
>>>> If its a national security threat its likely the other GNSS systems will be unavailable as well.
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> On Sep 6, 2018, at 9:53 AM, John Sloan <jsloan at diag.com> wrote:
>>>> 
>>>> 
>>>> Folks:
>>>> 
>>>> Well blow me down. It took some Google Maps fu on the web on my part, but
>>>> my time and place does indeed coincide with this “GPS Interference Testing” at
>>>> White Sands Missile Range. I just happened to be in my home office watching
>>>> several of my GPS-disciplined NTP servers when this occurred. Thanks, Graham!
>>>> 
>>>> :John
>>>> 
>>>>> ZDV   DENVER (ARTCC),CO. [Back to Top] !GPS 08/260 (KZDV A0287/18) ZDV NAV
>>>>> GPS (WSMR GPS 18-20) (INCLUDING WAAS, GBAS, AND ADS-B) MAY NOT BE AVBL WI A
>>>>> 359NM RADIUS CENTERED AT 333345N1063840W (TCS054036) FL400-UNL, 311NM
>>>>> RADIUS AT FL250, 215NM RADIUS AT 10000FT, 223NM RADIUS AT 4000FT AGL, 169NM
>>>>> RADIUS AT 50FT AGL DLY 1830-2230 1809031830-1809082230
>>>> 
>>>> --
>>>> J. L. Sloan            Digital Aggregates Corp.
>>>> +1 303 940 9064 (O)    3440 Youngfield St. #209
>>>> +1 303 489 5178 (M)    Wheat Ridge CO 80033 USA
>>>> jsloan at diag.com        http://www.diag.com <http://www.diag.com/>
>>>> 
>>>> 
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>>> 
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