Re: [time-nuts] time-nuts Digest, Vol 130, Issue 27
Hi Bob, You are confusing the readers here. 1) zero altitude relative the WGS84/GPS ellipsoid are often tens of meters over or below sea level, depending on your location. 2) zero altitude relative to a geoid (EGM96 or something else) is very close to sea level. Then if you think of the ellipsoid as a second order model of the geoid... we can start comfusing people again. -- Björn Hi The gotcha is that the GPS numbers are related to a geoid model and not to sea level. You can indeed find points that are âunderwaterâ based on the geoid, but quite dry in real life (and vice-versa). Bob On May 19, 2015, at 12:26 PM, Demian Martin demianm@gmail.com wrote: I would buy that (Google Maps being off) except that I'm less than 2 miles from the SF bay and -5M would have me underwater. That may well happen but not for a few years at least. Also the Arbiter does match Google maps pretty closely. It doesn't really matter a lot, just a curiosity. Demian Date: Mon, 18 May 2015 18:12:58 -0400 From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt Height Error Message-ID: 1ae37b6b-35fd-4c5f-95d6-01316d6c4...@n1k.org Content-Type: text/plain; charset=us-ascii Hi The simple answer is that Google maps may or may not be correct. There are a lot of examples of them being off by 10M or more. That said, my *guess* would be that the Thunderbolt is closer to the truth. Bob On May 18, 2015, at 2:34 AM, Demian Martin demianm@gmail.com wrote: I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old but it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It has the 1995 firmware issue, and I could get new firmware for it ($$) but I'm not using it as a clock, just a frequency source. I just moved and have re-setup both. They share an antenna. I got both to do a self survey. The Arbiter was really close to what Google maps indicate is my location. The Thunderbolt was about the same except it has me underground. The arbiter has the height as +30M. The Thunderbolt as -6M. What setting do I have wrong in the Thunderbolt? Would it affect the operation as a frequency standard in any way? Demian Martin San Leandro, CA 94577 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] time-nuts Digest, Vol 130, Issue 27
Hi One of our standing jokes when we lived by the shore was that we actually lived underwater. The GPS routinely put is 30 to 50’ below sea level …. Bob On May 20, 2015, at 3:36 AM, Björn Gabrielsson b...@lysator.liu.se wrote: Hi Bob, You are confusing the readers here. 1) zero altitude relative the WGS84/GPS ellipsoid are often tens of meters over or below sea level, depending on your location. 2) zero altitude relative to a geoid (EGM96 or something else) is very close to sea level. Then if you think of the ellipsoid as a second order model of the geoid... we can start comfusing people again. -- Björn Hi The gotcha is that the GPS numbers are related to a geoid model and not to sea level. You can indeed find points that are âunderwaterâ based on the geoid, but quite dry in real life (and vice-versa). Bob On May 19, 2015, at 12:26 PM, Demian Martin demianm@gmail.com wrote: I would buy that (Google Maps being off) except that I'm less than 2 miles from the SF bay and -5M would have me underwater. That may well happen but not for a few years at least. Also the Arbiter does match Google maps pretty closely. It doesn't really matter a lot, just a curiosity. Demian Date: Mon, 18 May 2015 18:12:58 -0400 From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt Height Error Message-ID: 1ae37b6b-35fd-4c5f-95d6-01316d6c4...@n1k.org Content-Type: text/plain; charset=us-ascii Hi The simple answer is that Google maps may or may not be correct. There are a lot of examples of them being off by 10M or more. That said, my *guess* would be that the Thunderbolt is closer to the truth. Bob On May 18, 2015, at 2:34 AM, Demian Martin demianm@gmail.com wrote: I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old but it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It has the 1995 firmware issue, and I could get new firmware for it ($$) but I'm not using it as a clock, just a frequency source. I just moved and have re-setup both. They share an antenna. I got both to do a self survey. The Arbiter was really close to what Google maps indicate is my location. The Thunderbolt was about the same except it has me underground. The arbiter has the height as +30M. The Thunderbolt as -6M. What setting do I have wrong in the Thunderbolt? Would it affect the operation as a frequency standard in any way? Demian Martin San Leandro, CA 94577 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] time-nuts Digest, Vol 130, Issue 27
Hi The gotcha is that the GPS numbers are related to a geoid model and not to sea level. You can indeed find points that are “underwater” based on the geoid, but quite dry in real life (and vice-versa). Bob On May 19, 2015, at 12:26 PM, Demian Martin demianm@gmail.com wrote: I would buy that (Google Maps being off) except that I'm less than 2 miles from the SF bay and -5M would have me underwater. That may well happen but not for a few years at least. Also the Arbiter does match Google maps pretty closely. It doesn't really matter a lot, just a curiosity. Demian Date: Mon, 18 May 2015 18:12:58 -0400 From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt Height Error Message-ID: 1ae37b6b-35fd-4c5f-95d6-01316d6c4...@n1k.org Content-Type: text/plain; charset=us-ascii Hi The simple answer is that Google maps may or may not be correct. There are a lot of examples of them being off by 10M or more. That said, my *guess* would be that the Thunderbolt is closer to the truth. Bob On May 18, 2015, at 2:34 AM, Demian Martin demianm@gmail.com wrote: I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old but it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It has the 1995 firmware issue, and I could get new firmware for it ($$) but I'm not using it as a clock, just a frequency source. I just moved and have re-setup both. They share an antenna. I got both to do a self survey. The Arbiter was really close to what Google maps indicate is my location. The Thunderbolt was about the same except it has me underground. The arbiter has the height as +30M. The Thunderbolt as -6M. What setting do I have wrong in the Thunderbolt? Would it affect the operation as a frequency standard in any way? Demian Martin San Leandro, CA 94577 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] time-nuts Digest, Vol 130, Issue 27
I would buy that (Google Maps being off) except that I'm less than 2 miles from the SF bay and -5M would have me underwater. That may well happen but not for a few years at least. Also the Arbiter does match Google maps pretty closely. It doesn't really matter a lot, just a curiosity. Demian Date: Mon, 18 May 2015 18:12:58 -0400 From: Bob Camp kb...@n1k.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Thunderbolt Height Error Message-ID: 1ae37b6b-35fd-4c5f-95d6-01316d6c4...@n1k.org Content-Type: text/plain; charset=us-ascii Hi The simple answer is that Google maps may or may not be correct. There are a lot of examples of them being off by 10M or more. That said, my *guess* would be that the Thunderbolt is closer to the truth. Bob On May 18, 2015, at 2:34 AM, Demian Martin demianm@gmail.com wrote: I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old but it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It has the 1995 firmware issue, and I could get new firmware for it ($$) but I'm not using it as a clock, just a frequency source. I just moved and have re-setup both. They share an antenna. I got both to do a self survey. The Arbiter was really close to what Google maps indicate is my location. The Thunderbolt was about the same except it has me underground. The arbiter has the height as +30M. The Thunderbolt as -6M. What setting do I have wrong in the Thunderbolt? Would it affect the operation as a frequency standard in any way? Demian Martin San Leandro, CA 94577 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] time-nuts Digest, Vol 130, Issue 27
Which altitude do you have the Thunderbolt set up to report? If you have the datum set to WGS-84, the Thunderbolt can report either HAE (height above ellipsoid) or MSL (height above the geoid model) in its serial output. The choice is controlled by bit 2 of byte 0 of the 0x35 command packet. This can be stored in EEPROM, which determines the power-up default. HAE is mathematically simpler to calculate but bears only an approximate relationship to actual sea level. MSL requires some sort of table (inside the GPS receiver) to specify the geoid model, but since it's a fit to the actual Earth, the altitude is more likely to agree to what you think of as altitude. Many GPS receivers provide a choice of which altitude they report in their output stream, so when comparing two receivers you need to check that both the datum and the HAE/MSL altitude choices are configured the same. This should not have any effect on timing. The GPS receiver knows where it is in Cartesian coordinates in all cases. Your choice of map datum controls the conversion to latitude and longitude that the receiver reports, while the choice of HEA/MSL controls the conversion to reported altitude, but these choices should affect this output conversion only. - Dave On May 18, 2015, at 2:34 AM, Demian Martin demianm@gmail.com wrote: I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is old but it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It has the 1995 firmware issue, and I could get new firmware for it ($$) but I'm not using it as a clock, just a frequency source. I just moved and have re-setup both. They share an antenna. I got both to do a self survey. The Arbiter was really close to what Google maps indicate is my location. The Thunderbolt was about the same except it has me underground. The arbiter has the height as +30M. The Thunderbolt as -6M. What setting do I have wrong in the Thunderbolt? Would it affect the operation as a frequency standard in any way? Demian Martin San Leandro, CA 94577 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
