[time-nuts] 58503A stats

Magnus Danielson magnus at rubidium.dyndns.org
Sun Aug 16 06:18:43 EDT 2015


Do not worry about that sky-view.
I'd guess your issue is more local, as on your roof.
Still, in timing you can afford to drop a lot of satellites if you only 
got a good fixed position.


On 08/04/2015 11:02 AM, Alan Ambrose wrote:
> p.s. here's the view south taken from about 2m below the antenna:
> https://www.dropbox.com/s/zejod2sfi4iogq1/IMG_460371644.JPG?dl=0
> Alan
> From: Alan Ambrose
> Sent: 04 August 2015 9:50 AM
> To: 'time-nuts at febo.com' <time-nuts at febo.com>
> Subject: 58503A stats
> Hi,
> Here is a screen capture from excellent Ulrich's Z38XX program:
> https://www.dropbox.com/s/6p5dr8apsftrckf/Z38XX-1.JPG?dl=0
> This is the first time that I've seen this output and I have a couple of questions. I should explain that the antenna is fairly well situated in London UK with a good view south with no obstacles and ~5m above and away from any other roofs. There are 3 small skyscrapers about ½ mile distance at 140° azimuth and 15° elevation. There are however obstructions about 4m away to the NW & SW (around 240° and 330°) limiting the view to 45° elevation. The device is a 58503A (it might be some dodgy far east 're-manufacture') with tracking of max 6 active sats. I've set the elevation mask temporarily to 0° to get the fullest map - as you can see that doesn't make much difference.
> + I was surprised to see such a noisy EFC signal - I assumed that the EFC changed v. gradually on a slow loop - maybe with temperature and aging. However there's a lot of high frequency crud there which I don't understand.
> + The 'holdover uncertainty predict' seems to go on a daily loop along with the EFC from 1.5 to 2.4us - presumably with temperature? If that's normal behaviour it suggests that the DOCXO isn't that well thermally managed?
> + The holdover uncertainty and the 1 pps variance don't relate at all to the occasional drop down to 3 sats. So some other effect is at work here - is this just ionosphere and general short term GPS inaccuracy only?
> + The time stability measures are not credible in their relentless plunge downward?
> + The azimuth/elevation chart looks about right except for the view to the south (say 150° to 220°) where I would expect at least as good as the view to the east - say by another 20° of elevation? (There's a point at 0/0 which I'm sure is an artefact caused by temporary '---' characters in the El/Az output of the device.) I don't have many ideas on this as the view is dead good. Any thoughts?
> + There's v little below 20° elevation - I think the view is clear though for most of the S azimuth down to ~0°. Is this simply because the device tends to ignore low elevation sats in its tracking because it has better ones to play with?
> Would all you greybeards out there give the benefit of your hard-won experience and/or maybe there are other people's charts to compare with?
> Regards, Alan
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