[time-nuts] Three-cornered hat on timelab?

Bob Stewart bob at evoria.net
Thu Apr 27 18:01:44 EDT 2017


Hi Bob,
OK, since we are in a low sunspot cycle, then it would follow that the 100ns movements would be rare.  Also, since I'm at about 29.8 degrees north, with few obstructions or reflectors to cause a problem, that improves what I'm capable of seeing out of what's available.  As to what problems are buried in my data due to equipment limitations, you're welcome to give me a long term loan of a nice H Maser and Timepod.  I promise I'll treat them well!  =)

Anyway, thanks for the explications.  As mentioned, I see figures bandied about on timenuts, but no explanation of the variables that cause those figures to be true or not true.  When I don't see them happening in my "lab", then I get confused.  I'm pretty certain I'm not the only one this happens to.  Several of you have been adamant about ionospheric effects north of 60ns.  I just haven't seen them.

Bob 

      From: Bob kb8tq <kb8tq at n1k.org>
 To: Bob Stewart <bob at evoria.net> 
Cc: Discussion of precise time and frequency measurement <time-nuts at febo.com>
 Sent: Thursday, April 27, 2017 4:17 PM
 Subject: Re: [time-nuts] Three-cornered hat on timelab?
   
Hi
Dig into space weather if you want to get into the details of the why and how often. It’s all out thereGoogle is your friend. Things like sun spot cycles are one of many drivers. The more perturbed the space weather is day to day, the more likely you are to see changes in the GPS.  Monitor the spaceweather sites on a regular basis and you will be able to make some guesses about what’s likely to happen. It’s only going to be a guess, no better than the 10 day weather forecast :) One of manysites: http://www.swpc.noaa.gov . A bit about what to watch for: http://www.swpc.noaa.gov/impacts/space-weather-and-gps-systemsThis one is a bit HF oriented: http://www.sws.bom.gov.au/HF_Systems/6/5
That’s only the first part.
The second part is that the delta ionosphere *is* fit by GPS data. What you are concerned with is not just a "bump' of space weather. You are concerned with one that does not fit well. That’s a normalthing when the weather is rough, but not an always thing.  A peak solar flux event that ramps upslow and decays slowly is very different than one with faster changes. You do get both. Patchydisruptions in the ionosphere are worse than a uniform high. They are hard to fit.
Next up …
The goodness of fit depends a lot on the sat’s you are using for your processing and where they arelocated in the sky. If you happen to have a sat that sends a signal across a big long patch of poorly fitionosphere,  you have a problem. If every single sat you are using is straight over head and your house is well fit, there is no problem.  Longer paths by their nature are more likely to be an issue.Bad fit only matters if you are depending to some extent on that part of the sky.  How much longer vs shorter contributes to your solution right now is always a “that depends” sort of thing. 
Is that all there is?
No, not hardly, that’s just the easy part. The troposphere also gets into the act and it flies around a bit. Last time I checked, they just use a static model there so it’s not a broadcast vs reality issue.You also get into things like location and sat angle from your location. If you are in northern Greenlandthings will be a bit different than in Ceylon. There are a few other issues I could probably dive into with a bit of research. 
So no, it’s not simple. How often do you see > 100 ns? Best data I’ve seen is that you hit that range a few times a year on average. More so at solar maxima and less so at solar minima. It’s no different than propagation on 10 meters. If you are looking for 100 ns every day, day in and day out, that’s not going to happen. 
You *are* looking for a peak to peak sort of swing. If you already have 20 ns wander in the data, you are going to have a hard time seeing anything much below 20 ns. What you are looking for is most likely to have a 86,000 second period (= day - night cycle). My guess is that you don’t see it because it’s buried in the noise of your data.
Not at all easy….
Bob


On Apr 27, 2017, at 3:10 PM, Bob Stewart <bob at evoria.net> wrote:
Hi Bob,
said:
"You have roughly 25 ns p-p in the data you show."
OK, here's a misunderstanding on my part right off the bat.  You see the swing as a p-p value, when I've been looking at it as only +/- 12.5ns from the trendline.

said some time ago:
"Now toss in the basics of GPS. Depending on the day, you will get <10 ns to  >100 ns swing over a  24 hour period. Today may or may not be the same as tomorrow."
So maybe I'm thinking too much about the >100ns figure, and not so much about the <10ns figure you mentioned.  The average doesn't seem to do much for me, either.  So, is the probability curve between 10ns and 100ns, where 100ns is least probable, of the type  y=2^-x?  IOW, in a year, I might see one 100ns swing, I would probably see at least one or two 50ns swings, and will probably see anything less than that multiple times, with the probably increasing as the value gets lower.

Not trying to crucify you with your own words, Bob.  Like many of the time-nuts who don't post, I'm just trying to make some sense of this in terms I can deal with.

Bob

     From: Bob kb8tq <kb8tq at n1k.org>
 To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Cc: Magnus Danielson <magnus at rubidium.se>
 Sent: Thursday, April 27, 2017 1:18 PM
 Subject: Re: [time-nuts] Three-cornered hat on timelab?
  
Hi


You have roughly 25 ns p-p in the data you show. There are a number of 10 ns “cycles” in the data. 
Any of this *may* be due to ionosphere. They also could be due to other issues.  With ~4.4 days of noisy
data, it may be tough to spot a trend. Since the ionosphere is a bit random, there is no guarantee that
you *will* always see a pretty sinusoidal trend line through the data. It’s a good bet that things quiet down
around midnight. There is no guarantee that they always go nuts (or go nuts to the same degree) around noon. 

Bob


> On Apr 27, 2017, at 12:48 PM, Bob Stewart <bob at evoria.net> wrote:
> 
> Hi Magnus,
> Try as I might, the weather and the local power company had other ideas about my long term capture.  I'm running everything but the 5370 from a UPS.  I guess I'm going to have to get batteries for my other UPS and run the 5370 from that.  A one second power loss was all it took to stop the test.
> 
> Anyway, I did manage to get 376,238 points of data.  The data is captured on a 5370A.  The external clock input and the STOP channel are fed by the 10MHz from my PRS-45A.  The START channel is fed by the 10MHz from one of my GPSDOs.  The EXT channel is fed by the 1PPS from another of my GPSDO units.  "EXT ARM" is enabled.  So, essentially, at every 1PPS pulse, the phase difference between the two 10MHz feeds is captured.
> 
> I've attached a screenshot of the phase plot which can also be found here:http://evoria.net/AE6RV/Timelab/Screenshot.png
> I've also made the timelab file (compressed by 7z) available here:
> http://evoria.net/AE6RV/Timelab/GFSvsCS.4.22.17.7z
> 
> So, back to my question:  Where are the large ionospheric phase moves?  This question has been causing me doubt since I started on this project.  Or don't I still have enough data collected for this to happen?
> 
> Bob
> 
> -----------------------------------------------------------------
> AE6RV.com
> 
> GFS GPSDO list:
> groups.yahoo.com/neo/groups/GFS-GPSDOs/info
> 
>      From: Magnus Danielson <magnus at rubidium.dyndns.org>
> To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
> Cc: magnus at rubidium.se
> Sent: Tuesday, April 18, 2017 1:09 AM
> Subject: Re: [time-nuts] Three-cornered hat on timelab?
> 
> Hi Bob,
> 
> That is a good solution indeed. Good luck with that measurement run!
> 
> One of the fun stuff with Timelab is that you can walk by and check the 
> developments. I've found that very useful for long measurements (as in 
> hours and days).
> 
> I prepared a cesium for one vendor, and initially they did not care so 
> much, but then they saw more deviations between the receivers, so they 
> wanted to sort it out, but discovered that they could not cancel out the 
> common mode of GPS signals (and its shifts), so then firing up that 
> cesium was the right thing. I remember writing support emails while 
> waiting for the airplane in Madrid airport, happy that they was doing a 
> first run for the right measurement reason. :)
> 
> Cheers,
> Magnus
> 
> On 04/18/2017 04:25 AM, Bob Stewart wrote:
>> Hi Magnus,
>> Today I started a long run against my PRS-45A.  Maybe this time I won't have a power outage.  I'll see what it tells me in a few days.
>> Bob
> 
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