Mike, A quick answer to this - two reasons why...
1) Your Thunderbolt is using WGS84 coordinate system and not USGS, and.. 2) The altitude fix is usually the most inaccurate parameter, as it is very unlikely that you have a GPS bird directly overhead. Think of your position fix as you sitting inside a sphere of probability. In the ideal world with perfect GPS geometry it would be a sphere, but in reality it is an ellipsoid due to less accuracy in the Z plane. Why, after setting (and assuming storing) a known accurate position it changes again, I don't know, unless the unit is reverting to a survey mode. I don't know this product intimately, so I'm sure others will proffer better suggestions. Rob Kimberley -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Michael Baker Sent: 29 March 2008 12:50 To: [email protected] Subject: [time-nuts] Another Trimble Tbolt question.... Hello, All-- Thanks to the collective savvy of this list and the patient assistance of Ken Winterling <wa2lbi> I was finally able to get my Tbolt to stop requiring me to configure the COM-4 channel every time I ran the monitoring software. So-- I had such good luck with that question, I'm going to pester the group with one more Tbolt question: In the "Position" area of the Tbolt monitoring display my altitude is given as 1.4 meters. The USGS topo map and a recent survey both say that the ground level at my house is 84 feet above MSL. The antenna for the T-bolt is on the top of my house 19 feet above the ground. If I open SETUP / POSITION and "SET ACCURATE POSITION" to, say....: 28 meters and enter that value, the indicated altitude changes to 28 meters, but the next day or so, I always find that it has reverted to 1.4 meters. Admittedly, having a (relatively) accurate altitude display is of minor importance to me since my primary reason for having the Tbolt is for a decent 10MHz reference. However, as a matter of principle it would be nice to have the altitude display be a little closer! Any suggestions as to how to get the Tbolt to display a more correct altitude? Thanks! Mike Baker WA4HFR Micanopy, FL --------------------- _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
