Hi Bob, This argument has been done before on time-nuts... sorry for repeating.
There are geodetic quality GPS reveivers, like the Ashtech Z12-CORS (with external 5-20MHz input - not the true Z12 Metronome) available for a few hundred dollars occasionally. I got my Z12 CORS for free, from a site where it had been replaced by modern GPS/GLONASS receivers. I also found three Novatel Millenium OEM3 for ca $100 a piece, which in their days were used by national time labs. Unfortunately two of them has developed a problem with a custom IC. I am far from having the economic freedom to purchase a new H-Maser or Cesium. However I still have a HP5065A running in the basement. When new in the early 1970ties, you could probably have traded the rubidium for the house it is now running in. Conclusion: used geodetic gps equipment are no more expensive, than many of the oscillators we play with. They might actually once have been used in the same national time lab... ;-) -- Björn > Hi > > Indeed true for most non-geodetic gps units. Put another way - true unless > you have a lot of money. > > Bob > > On Sep 9, 2012, at 7:25 PM, [email protected] wrote: > >> Hi Bob, >> >> Probably true for Motorola Oncores. Not very true for geodetic >> receivers. >> >> Until you have a receiver clock that is on par with the satellite clocks >> AND you are short on visable satellites. This might be true if you can >> load up a modern cesium in your vehicle, and go for a downtown "urban >> valley" type of scenario. >> >> On a stationary site, your expensive clock will not matter to much, >> since >> your solution is already pretty over-determined with some 60 >> measurements >> on each epoch. (9 GPS +6 Glonass)*2(L1/L2)*2 (code + phase) >> >> -- >> Björn >> >>> Hi >>> >>> Position accuracy and timing accuracy are two very different things. >>> Firmware is optimized to improve either one. "Position" firmware is >>> often >>> pretty poor for timing. >>> >>> Bob >>> >>> On Sep 9, 2012, at 5:05 PM, Chris Albertson <[email protected]> >>> wrote: >>> >>>> On Sun, Sep 9, 2012 at 1:14 PM, <[email protected]> wrote: >>>> >>>>> True for a cheap oem navigation receiver. Not true for a geodetic >>>>> quality >>>>> receiver, who usually have some options (external frequency input, >>>>> PPS_in) >>>>> to make them the best timing receivers available. However they are >>>>> much >>>>> more expensive than the typical single frequency timing reciver. >>>> >>>> I looked at every link and can't see where they give a timing accuracy >>>> spec on the PPS with respect to UTC. Possition accurracy is very >>>> good and we might assume the timing is as good. But they don't say it >>>> is. What's interesting is these GPSes will accept an accurate clock >>>> input in order to give better location data. That is the opposite of >>>> a timing GPS where you tell it accurate location data so that it can >>>> get better timing. Cutting down the unknown in one lets you do >>>> better in the other. I assume these all cost well over $50. You can >>>> get a pretty good timing GPS for $30 and it WILL have the PPS error >>>> specified. >>>> >>>> To the OP. None of this matters a lot because PPS is a standard input >>>> signal. It is easy to swap out a GPS receiver later. Same with the >>>> OCXO. From a control point of view they are all pretty much the same. >>>> You can swap them out later >>>> >>>> >>>> Chris Albertson >>>> Redondo Beach, California >>>> >>>> _______________________________________________ >>>> 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. >>> >> >> >> >> _______________________________________________ >> 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. > _______________________________________________ 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.
