[time-nuts] Three-cornered hat on timelab?
bob at evoria.net
Thu Apr 27 15:10:21 EDT 2017
"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.
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?
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.
> 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:
> 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?
> GFS GPSDO list:
> 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. :)
> 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.
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