+geojibby Posted June 24, 2010 Share Posted June 24, 2010 Quick question: do car-based GPSrs like my Nüvi 255 pick up different satellites than trail-based GPSr (60Cx)? Reason I ask is when I had them both on the satellite screen the other day, the Nüvi was picking up a couple satellites that weren't even showing up on my Cx. Coincidentally (), the Nüvi was estimating it's accuracy consistently at ±3m vs. the ±4m of my Cx. Any thoughts? Quote Link to comment
jholly Posted June 24, 2010 Share Posted June 24, 2010 Quick question: do car-based GPSrs like my Nüvi 255 pick up different satellites than trail-based GPSr (60Cx)? Reason I ask is when I had them both on the satellite screen the other day, the Nüvi was picking up a couple satellites that weren't even showing up on my Cx. Coincidentally (), the Nüvi was estimating it's accuracy consistently at ±3m vs. the ±4m of my Cx. Any thoughts? Oh, yes, there are three sets of satellites. One for cars and planes, one for use on the trail and one for bombs. And if you believe that I have a bridge for sale on Puget Sound. No, it is just what ever the units lock on to. Quote Link to comment
MtnHermit Posted June 24, 2010 Share Posted June 24, 2010 And if you believe that I have a bridge for sale on Puget Sound. No, it is just what ever the units lock on to.How about selling Galloping Gertie, IIRC the name for the Tacoma Narrows bridge. Perfectly tuned for high winds. Quote Link to comment
jholly Posted June 24, 2010 Share Posted June 24, 2010 And if you believe that I have a bridge for sale on Puget Sound. No, it is just what ever the units lock on to.How about selling Galloping Gertie, IIRC the name for the Tacoma Narrows bridge. Perfectly tuned for high winds. I could but unfortunately it is laying on the bottom of the Narrows with the remains of Tubby. But I do have two other nice bridges there for sale. Quote Link to comment
+geojibby Posted June 25, 2010 Author Share Posted June 25, 2010 My GPSMAP 60Cx has never locked onto the ones the Nüvi did. They don't ever show up on the bottom signal register. Why would that be??? Quote Link to comment
+RRLover Posted June 25, 2010 Share Posted June 25, 2010 Cx vs. Nuvi = different chipsets w/different sensitivity twixt the two? Just a guess. Norm Quote Link to comment
Grasscatcher Posted June 25, 2010 Share Posted June 25, 2010 If multiple GPS are at the same location, then each one SHOULD see exactly the same satellites, both in Sat ID and in Quantity. Use Trimble Planning (free) software and you can determine which specific sats your unit should see at any given location at any given time, whether past or present, current location or other theoretical location. Quote Link to comment
+geojibby Posted June 25, 2010 Author Share Posted June 25, 2010 That's why it was puzzling to me. Both units in the same location should be picking up the same birds. But as I mentioned, the Nüvi was picking up different ones than the Cx. Strange. If multiple GPS are at the same location, then each one SHOULD see exactly the same satellites, both in Sat ID and in Quantity. Use Trimble Planning (free) software and you can determine which specific sats your unit should see at any given location at any given time, whether past or present, current location or other theoretical location. Quote Link to comment
+dfx Posted June 25, 2010 Share Posted June 25, 2010 That's why it was puzzling to me. Both units in the same location should be picking up the same birds. But as I mentioned, the Nüvi was picking up different ones than the Cx. Strange. "seeing" is not always the same as "seeing". GPS chips have several internal thresholds, including elevation above horizon and signal level. for example, if the satellite is 10 degrees above the horizon and the chip's threshold is set to 15 degrees, it will ignore it, meaning it won't even show up as being there. signal level is different, it will still see it if the signal level is below the threshold, but will not start tracking it. of course, different chips will behave differently. Quote Link to comment
MtnHermit Posted June 25, 2010 Share Posted June 25, 2010 "seeing" is not always the same as "seeing". GPS chips have several internal thresholds, including elevation above horizon and signal level. for example, if the satellite is 10 degrees above the horizon and the chip's threshold is set to 15 degrees, it will ignore it, meaning it won't even show up as being there. signal level is different, it will still see it if the signal level is below the threshold, but will not start tracking it. of course, different chips will behave differently.Didn't know that could be done, but why not. Clearly these are very different chips by different companies so one would expect differences. Bottom line: People are obsessive compulsive about accuracy, real or perceived. Quote Link to comment
Grasscatcher Posted June 25, 2010 Share Posted June 25, 2010 I've never heard of a "Chipset" having an elevation mask threshold.??? Regardless, exactly the same predetermined "set" of sats (almanac)are "available" to however many GPSs are at a particular time/location. Whether they "choose" to use them (lock on with solid bar) due to signal strength, horizon elevation mask, etc, is a different story. Whether they are used or not, the same numbers should be listed across the bottom of the page, whether bar is solid or not. You can tell what that specific list of sats "should" be by using the Trimble planning software. Quote Link to comment
+dfx Posted June 25, 2010 Share Posted June 25, 2010 I've never heard of a "Chipset" having an elevation mask threshold.??? http://www.linkspoint.com/toolkithelp/Sirf...vationMask.html Regardless, exactly the same predetermined "set" of sats (almanac)are "available" to however many GPSs are at a particular time/location. Whether they "choose" to use them (lock on with solid bar) due to signal strength, horizon elevation mask, etc, is a different story. Whether they are used or not, the same numbers should be listed across the bottom of the page, whether bar is solid or not. You can tell what that specific list of sats "should" be by using the Trimble planning software. no, see above. if a satellite is ignored for whatever reason, such as elevation mask, it doesn't even show up. Quote Link to comment
Grasscatcher Posted June 25, 2010 Share Posted June 25, 2010 I've never heard of a "Chipset" having an elevation mask threshold.??? http://www.linkspoint.com/toolkithelp/Sirf...vationMask.html Regardless, exactly the same predetermined "set" of sats (almanac)are "available" to however many GPSs are at a particular time/location. Whether they "choose" to use them (lock on with solid bar) due to signal strength, horizon elevation mask, etc, is a different story. Whether they are used or not, the same numbers should be listed across the bottom of the page, whether bar is solid or not. You can tell what that specific list of sats "should" be by using the Trimble planning software. no, see above. if a satellite is ignored for whatever reason, such as elevation mask, it doesn't even show up. I stand corrected! Thanks, Learn something every day.... Quote Link to comment
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.