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#1
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External GPS antenna and WAAS?
On Fri, 16 Jan 2004 15:59:48 -0800, "Chuck Tribolet"
wrote: On the west coast, the WAAS birds are only about 15 degrees above the horizon, so it's really easy to loose them on land. The good news is that they stay locked up well on the ocean, at least in the Monterey area. As long as your GPS has a clear view to the southwest, it should work fine. Travel direction isn't relevant, except as it might make part of the boat hide the bird. You learn something new everyday - I didn't know that. Interesting - thanks. Later, Tom S. Woodstock, CT ---------- "My rod and my reel - they comfort me." St. Pete, 12 Lb. Test |
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#2
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External GPS antenna and WAAS?
To find the angle of the geostationary WAAS satellites from your area,
go to: http://www.directv.com/DTVAPP/DishPointerAction.do at Direct TV and put your zip code into the box on the page. DTV will tell you how to set the elevation on your DTV dish and that angle is the angle the WAAS birds are from your latitude. All geostationary satellites occupy the same 22,800 mile band around the equator. For Charleston, SC, the data comes back: For your zip Code 29418 the azimuth and elevation are displayed below: DIRECTV Dish Pointer Azimuth 220.9 Elevation 45.6 The Azimuth is irrelevant to WAAS birds. The elevation above the horizon is the same. This is also the elevation if you have a 137 Mhz GOES weather satellite receiver or any other geostationary satellite use. The higher, the better, of course. The direct satellite radios like XM and Sirius work better in the South, too...(c; Larry W4CSC |
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#4
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External GPS antenna and WAAS?
On Sat, 17 Jan 2004 19:59:00 GMT, Short Wave Sportfishing
wrote: Now that's two new things I learned today. I keep this up, I might get smart or something. Later, Tom S. Woodstock, CT We're holding Captain's Mast on the main deck later on this afternoon. Many sailors learn all kinds of new things, every time we hold it.... Keel hauling will be first thing in the morning, tomorrow. THIS time we're going to try it WITHOUT the engine running, too! Last time was a little 'messy' and the sharks followed us for a week! Larry W4CSC |
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#5
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External GPS antenna and WAAS?
Larry, this is one of the rare occasions when you are wrong. Different
geostationary birds will have different elevations. The one straight south of you will have an elevation of about 90 minus latitude degrees and will be the highest. One 180 degrees around the world will have a negative elevation. -- Chuck Tribolet http://www.almaden.ibm.com/cs/people/triblet Silicon Valley: STILL the best day job in the world. "Larry W4CSC" wrote in message ... To find the angle of the geostationary WAAS satellites from your area, go to: http://www.directv.com/DTVAPP/DishPointerAction.do at Direct TV and put your zip code into the box on the page. DTV will tell you how to set the elevation on your DTV dish and that angle is the angle the WAAS birds are from your latitude. All geostationary satellites occupy the same 22,800 mile band around the equator. For Charleston, SC, the data comes back: For your zip Code 29418 the azimuth and elevation are displayed below: DIRECTV Dish Pointer Azimuth 220.9 Elevation 45.6 The Azimuth is irrelevant to WAAS birds. The elevation above the horizon is the same. This is also the elevation if you have a 137 Mhz GOES weather satellite receiver or any other geostationary satellite use. The higher, the better, of course. The direct satellite radios like XM and Sirius work better in the South, too...(c; Larry W4CSC |
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#6
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External GPS antenna and WAAS?
On Sat, 17 Jan 2004 19:35:20 -0800, "Chuck Tribolet"
wrote: Larry, this is one of the rare occasions when you are wrong. Different geostationary birds will have different elevations. The one straight south of you will have an elevation of about 90 minus latitude degrees and will be the highest. One 180 degrees around the world will have a negative elevation. -- Chuck Tribolet http://www.almaden.ibm.com/cs/people/triblet You are correctimundo, however as the GPS antenna is not pointable, the website will give them a fair idea, within a few degrees, of the elevation of any geostationary bird from their zip code. The further north you go the worse the problem. The website won't tell them EXACTLY how bad it is, but will give them a general idea..... Hmm.....we could take one of these gyro stabilized DirecTV dishes, replace the 10 Ghz feedhorn with a WAAS feed horn.....Nope, we're gonna need a bigger dish to make it have more gain.....(c; HEY, my neighbor has one of those REALLY BIG old satellite antennas that's scrambled now he's not using!........hee hee. On a more serious note, I don't believe the GPS has to have CONSTANT WAAS data to make it accurate. The drift you get corrected for is VERY slow moving, so if it had a lock on WAAS data every few minutes that should be good enough for good correction, shouldn't it? I'd think the manufacturers would tell the receiver to use the LAST available data until new data arrives. Larry W4CSC |
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#7
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External GPS antenna and WAAS?
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#8
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External GPS antenna and WAAS?
That "error" calculation may not include the accuracy added by WAAS.
And it is a SWAG based on satellite geometry at the moment, and the two receivers may use different SWAGs. -- Chuck Tribolet http://www.almaden.ibm.com/cs/people/triblet Silicon Valley: STILL the best day job in the world. "Short Wave Sportfishing" wrote in message ... On Sun, 18 Jan 2004 17:03:57 GMT, (Larry W4CSC) wrote: On a more serious note, I don't believe the GPS has to have CONSTANT WAAS data to make it accurate. The drift you get corrected for is VERY slow moving, so if it had a lock on WAAS data every few minutes that should be good enough for good correction, shouldn't it? I'd think the manufacturers would tell the receiver to use the LAST available data until new data arrives. It is my understanding that the software in WAAS enabled receivers do not check constantly - that is my understanding. Curiously enough, I have a Magellon 315 and 330M and the 315 is a tad more accurate (will show zero error for instance) than the 330 (I never get zero error) which is WAAS enabled. When I first noticed that, I thought that the WAAS receiver would be more accurate. Later, Tom S. Woodstock, CT ---------- "My rod and my reel - they comfort me." St. Pete, 12 Lb. Test |
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#9
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External GPS antenna and WAAS?
On Sun, 18 Jan 2004 14:11:09 -0800, "Chuck Tribolet"
wrote: That "error" calculation may not include the accuracy added by WAAS. And it is a SWAG based on satellite geometry at the moment, and the two receivers may use different SWAGs. Good point. Later, Tom S. Woodstock, CT ---------- "My rod and my reel - they comfort me." St. Pete, 12 Lb. Test |
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#10
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External GPS antenna and WAAS?
On Sun, 18 Jan 2004 19:57:09 GMT, Short Wave Sportfishing
wrote: It is my understanding that the software in WAAS enabled receivers do not check constantly - that is my understanding. Curiously enough, I have a Magellon 315 and 330M and the 315 is a tad more accurate (will show zero error for instance) than the 330 (I never get zero error) which is WAAS enabled. When I first noticed that, I thought that the WAAS receiver would be more accurate. Aboard Lionheart, leaving the Raymarine Raystar 120 Seatalk WAAS-GPS and its RL70CRC Plus radar display/chartplotter on for long periods of time tied to E-dock, I plot the Raystar 120's position centered around its position on the hard top varying from about 30' off the stern to near the bow to about halfway across the boats next door to port and starboard, easily within the 3 meter accuracy circle that's specified. The boat's in Charleston, SC, so has good WAAS view at about 45 degrees elevation. It's not quite good enough for ILS approach, but damned close! Clicking the waypoints on top of a bouy symbol is NOT a good idea.... Larry W4CSC |
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