Useless Constellation.
Posted By Lawrence Paul Lopresti on 1/24/2004 at 9:31 AM

While fiddling with my ProMarks last night in Navigation mode I watched a pretty useless constellation of satellites. At 11 PM Eastern my skyplot showed 10 satellites, that is good.
However from NW to the zenith 5 were lined up (5° spread tops) with touching and overlapping symbols.
They were PRNs 03, 23, 22, 15, 18
also 26, 29 were paired up in the NE
21 and 09 were in the SE near the zenith and lonely 14 was the only satellite in the SW.

Since I was in my bedroom and didn't have an antenna handy I couldn't get a PDOP but I imagine it was very high. By 11:35 09 had moved up to join the long string and 05 had come into view in the SE. For a while I had 11 satellites displayed.

Oops I posted before I was done.

Now my questions.

The Promark records 10 satellites, how does it decide which one not to record when there are more than 10 observable? It appears that at least 12 can be displayed across the bottom. can I tell it which satellites to ignore. I was surprised to see 23 as it just spent 20 days off line.

Who knows exactly what the logic is in the orbit arrangements? 18 is in slot E4, 22 in E2 and 23 in E5. 20 is in slot E1 but was not in the sky. 26 in F2 and 29 in F5 are also paired up out of orbital sequence. Aren't the orbital slots in order in the plane? 3 satellites in one plane means they should line up more or less, but 03 in C2 and 15 in D5 really hung around like they were also in the same orbital plane.

At 11:35 8 of the satellites were North of my position and I am at 40°40' latitude.

Paul in PA
Modified By Lawrence Paul Lopresti on 1/24/2004 at 9:49 AM

Re: Useless Constellation.
Posted By Phil athome on 1/24/2004 at 3:21 PM

I did not go do any reading about this but I think the rule is that if you are getting more signals than you can handle the receiver picks the strongest signals. I may be wrong. Does anyone have a field test that shows this one way or the other?



Re: Useless Constellation.
Posted By Scott Partridge on 1/24/2004 at 5:11 PM

Remember that the skyplot is a 2D display and the satellites are in 3D space. The elevation of the satellite above the horizon is just as important as the spread in azimuth. I wouldn't rely much on the skyplot without a current almanac loaded anyway.

As for which satellites it uses, I guess that it would be a combination of PDOP, elevation mask, and signal-to--noise ratio.

I can't honestly say that I've worried about a high PDOP for as long as I can remember.



Re: Useless Constellation.
Posted By John Francis on 1/24/2004 at 7:35 PM

I had 5-7 sats at about 2:45 pm, all pretty much aligned SW to NE(maybe 5-10 degrees spread) and a PDOP of no doubt, 20 plus(it was completely off the chart)


Re: Useless Constellation.
Posted By jerry wahl on 1/25/2004 at 7:27 AM

Gee, wasn't there someone on here or the other board just about a week ago that was bragging that there are so many birds up now they didn't ever need to do mission planning?

- jlw


Re: Useless Constellation.
Posted By Lawrence Paul Lopresti on 1/25/2004 at 9:50 AM

There are 29 birds up there, but because of how they are located in their planes they are only as usefull as 22, which is less than the required 24. I am expunding on this on the main board, as soon as I finish some research.

Paul in PA
Modified By Lawrence Paul Lopresti on 1/25/2004 at 10:03 AM

Re: Useless Constellation.
Posted By John Francis on 1/25/2004 at 11:37 AM

I guess my post yesterday(very high PDOP) was because of a year old almanac. I'm attempting now to get the planning module to stop going to the damned "My Document" folder for information.