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Sep 11th GPS reception


scotthsi
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I saw some posts about GPS coverage/reception being affected in parts of the country on or around September 11th. Anyone notice such a thing?

I was out caching most of the day on 9/11, and I didn't notice any difference in coverage or reception. I found 15 caches and wasn't able to find 2 others, which is pretty typical for me. And the estimate of error on my 60CSx was around 20 feet all day, which again is fairly typical.

 

--Larry

Edited by larryc43230
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Not specifically on the 11th, but lately I've been seeing more sats at night than I am during the day. I know this is normal based on their orbit. However, standing in a spot in my back yard in mid day my 60 would pick up around 8 birds. Then, at that same spot, sometime after midnight, I'd have all 12 channels full with a considerably lower EPE. I've tried looking at Trimble's planning software, but haven't taken the time to figure everything out yet. Looks like I've got some more reading to do.

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I saw some posts about GPS coverage/reception being affected in parts of the country on or around September 11th. Anyone notice such a thing?

 

Hmm, the only advisory I saw was:

GPS USERS MAY EXPERIENCE A TEMPORARY DEGREDATION IN GPS RECEIVER RECEPTION IN THE FOLLOWING AREAS, SOUTHERN NEBRASKA, KANSAS, OKLAHOMA, SOUTHWESTERN ARKANSAS, EASTERN TEXAS, AND WESTERN LOUISIANA FROM 111302Z - 111323Z SEP 09 DUE TO SATELLITE MAINTENANCE.

 

Is this what you were referring to?

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Yup...just wondering if anyone in those areas noticed anything screwy with their GPS units during that time.

Since it only lasted 21 seconds, I doubt if anyone using consumer-grade GPSs noticed anything.

 

I get your point, but if you understood Julian date/time, you're realize it was 21 minutes. :laughing:

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Yup...just wondering if anyone in those areas noticed anything screwy with their GPS units during that time.

Since it only lasted 21 seconds, I doubt if anyone using consumer-grade GPSs noticed anything.

 

I get your point, but if you understood Julian date/time, you're realize it was 21 minutes. :D

 

I do understand Julian time. More importantly, I understand what the "Z" abbreviation means. That's Zulu (UTC to be precise) time, and 21 seconds is the correct time span.

 

Julian time is presented as a decimal portion of a Julian Day (JD). The value presented here was a whole number (followed by the Zulu designation). It is NOT a Julian time value. Nor does it make any sense that they would mix a Gregorian date with a Julian time.

 

Furthermore, there's no possible way to get 21 minutes out of those two values, using the Julian system. 111302 - 111323 would be a span of 21 DAYS, and they would have occurred centuries ago (4409 BCE). If taken as Julian time (which is wrong on the face of it, since there's no decimal point, and values less than a day are fractional), then .111302 - .111323 would be about 2 seconds, not 21 minutes.

 

While a 21 second degradation of service is meaningless to us, there are those to whom it is not. It shouldn't be surprising that they issue a notice for it. If you think otherwise, you don't have an appreciation of all the applications GPS is used for.

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Here's a writeup on the cause of this. Read the "HDOP Warning." section.

 

Incidentally, another HDOP was issued today:

GPS Users may experience a temporary degradation in GPS receiver

reception approximately 240 NM east of Hawaii from 221636Z - 221639Z Oct

09 due to satellite maintenance.

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111302Z SEP 09 is a 'DTG' (Date/Time Group), it's a military format and a NATO standard.

 

It means 11(day) 1302Z (time) SEP 09 (month/year obviously) so the time was 21 minutes. The period was from 1.02PM until 1.23PM on 11th September. Anyone used to reading military signals would recognise this straight away, however it's not a very 'intuitive' format that often confuses people at first.

Edited by nzgunnie
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Unless it is Iso-8601 standard, in which case it would mean 21 seconds.

UTC

If the time is in UTC, add a 'Z' directly after the time without a space. 'Z' is the zone designator for the zero UTC offset. "09:30 UTC" is therefore represented as "09:30Z" or "0930Z". "14:45:15 UTC" would be "14:45:15Z" or "144515Z".

UTC time is also known as 'Zulu' time, since 'Zulu' is the NATO phonetic alphabet word for 'Z'.

 

But as you mentioned, since they add the month and year at the end, the first 2 numbers must be the date.

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