GPS Satellite issue

7 years ago
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tbwonder
tbwonder
NSW
748 posts
NSW, 748 posts
20 Nov 2018 11:04pm
Noticed a funny scenario today. All afternoon I had 7-8 satellites locked (On my GT31) then at 5.00pm DST (Sydney time) things started to go bad, by 5.15pm I was down to only 5 and it stayed that way for the next 30 minutes before improving again. It didn't bother me as 5 is still enough to produce doppler speeds. Unfortunately a friend was 50 minutes into an hour attempt when his GW60 dropped to 4 satellites, thus producing invalid doppler data.
I looked at a few other tracks from KA72 and saw a similar thing.
Did anybody else notice this?

Is there a way to look at how many satellites should have been in view at that time?
decrepit
decrepit
WA
12872 posts
WA, 12872 posts
20 Nov 2018 10:02pm
There's a locosys survey out looks like they are planning a new unit. if you get to fill it in, request multiple GNNS if the watch also used glonass you'd have had plenty sats.
kato
kato
VIC
3527 posts
VIC, 3527 posts
21 Nov 2018 7:11am
decrepit said..
There's a locosys survey out looks like they are planning a new unit. if you get to fill it in, request multiple GNNS if the watch also used glonass you'd have had plenty sats.


Anyone got a link to the survey
tbwonder
tbwonder
NSW
748 posts
NSW, 748 posts
21 Nov 2018 8:48am
I am answering my own question:

This is the predicted satellite availability for 20-Nov-18 at Coal Point. It shows a poor area around 3-4pm. It doesn't exactly align with the issues that we had one hour later, but it is close.

You can find this data here satpredictor2.deere.com/homePost
It also does Glonass
Jacko51
Jacko51
SA
226 posts
SA, 226 posts
21 Nov 2018 9:35am
kato said..

decrepit said..
There's a locosys survey out looks like they are planning a new unit. if you get to fill it in, request multiple GNNS if the watch also used glonass you'd have had plenty sats.



Anyone got a link to the survey


www.facebook.com/LOCOSYS.Club/
BSN101
BSN101
WA
2390 posts
WA, 2390 posts
21 Nov 2018 12:04pm
survey done. My thoughts

Completely waterproof. Connects to multiple satellite systems. Long battery life when being used. Large memory. Floats. A basic model (ie. large screen, fixed at 5hz, waterproof, wireless charging BT/WiFi) & one that does it all (customizable to the need of the athlete). Wireless charging (like phones). Large screen to read details. Blue Tooth to connect with headphones for audible data updates while sailing.
sailquik
sailquik
VIC
6171 posts
VIC, 6171 posts
21 Nov 2018 8:21pm
See new thread regarding the survey
sailquik
sailquik
VIC
6171 posts
VIC, 6171 posts
21 Nov 2018 8:50pm
Thanks for prompting my interest in the issue of Satellite coverage Andrew.

I looked up the Sat coverage for Sandy Point on friday. Interesting,



That looks OK, at least after dawn.

But look how much better if we have a 'GPS' that can use Glonass as well!







yoyo
yoyo
WA
1646 posts
WA, 1646 posts
21 Nov 2018 8:59pm

This is the predicted satellite availability for 20-Nov-18 at Coal Point. It shows a poor area around 3-4pm. It doesn't exactly align with the issues that we had one hour later, but it is close.

Daylight saving????
fangman
fangman
WA
1906 posts
WA, 1906 posts
21 Nov 2018 9:20pm
sailquik said..
Thanks for prompting my interest in the issue of Satellite coverage Andrew.

I looked up the Sat coverage for Sandy Point on friday. Interesting,



That looks OK, at least after dawn.

But look how much better if we have a 'GPS' that can use Glonass as well!








Daffy, the graphs seem to have GMT as the reference time zone, maybe 11 hrs addition may might a difference?
tbwonder
tbwonder
NSW
748 posts
NSW, 748 posts
22 Nov 2018 9:30am
yoyo said..

This is the predicted satellite availability for 20-Nov-18 at Coal Point. It shows a poor area around 3-4pm. It doesn't exactly align with the issues that we had one hour later, but it is close.

Daylight saving????


I specified Australian Eastern Daylight Saving Time which is GMT +11, looks like Daffy didn't. The trouble is each time you change your location the time resets back to GMT
sailquik
sailquik
VIC
6171 posts
VIC, 6171 posts
22 Nov 2018 9:34am
opps!

But I guess my main point was how much better it is with Multi GNSS.

OK here is the corrected graph for AEDST:

Looks like we will have good coverage for the morning session. and in this case we are lucky because the lowere coverage count coincides with high tide and by the time we can sail again, coverage count should be higher again.




Of even more interest is that the coverage pattern almost repeats each day into the future. So when I looked at the next few days the yellow bars were almost in the same place. Then I skipped ahead by a week at a time and found that the lower count coverage patten is getting slightly earlier by around about 45 minutes each week, 3 hours per month.

here is 23 Dec 2018:






And January 23 2019:







Roo
Roo
882 posts
Roo Roo
882 posts
22 Nov 2018 7:02am
sailquik said..
opps!

But I guess my main point was how much better it is with Multi GNSS.


Daffy, run the GPS Logit bluetooth unit at 10hz and you'll get the multiple GPS system sats.
sailquik
sailquik
VIC
6171 posts
VIC, 6171 posts
22 Nov 2018 10:04am
Roo said..

sailquik said..
opps!

But I guess my main point was how much better it is with Multi GNSS.



Daffy, run the GPS Logit bluetooth unit at 10hz and you'll get the multiple GPS system sats.


Exactly my plan Roo!
JulienLe
JulienLe
405 posts
405 posts
22 Nov 2018 10:53am
Hello Andrew, GPS shows up 4 minutes earlier every day. :)

"The orbital period is one-half a sidereal day, i.e., 11 hours and 58 minutes so that the satellites pass over the same locations or almost the same locations every day. "
-- en.wikipedia.org/wiki/Global_Positioning_System
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