Yes, the "you need more stuff" is the most dangerous step. Soon you will need a time interval counter and you'll start to hunt for an SR620.
On Wed, Feb 22, 2012 at 11:03 PM, Bob Camp <[email protected]> wrote: > Hi > > Simple answers: > > 1) Your GPSDO is more accurate than your Rb > 2) Your Rb is more stable for short periods of time than your GPSDO > 3) Now you need more stuff... > > Bob > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Don Barr > Sent: Wednesday, February 22, 2012 3:15 PM > To: [email protected] > Subject: [time-nuts] A man with one used rubidium standard knows what 10MHz > is, more than one, not so much... > > Hi, > > (sorry to Tvb for stealing a good subject line) > > I'm just getting into clocks and oscillators, so please excuse any > ignorance. I like probably many new list watchers saw Dave Jones of > EEVBlog fame with his used FE-5680A and thought - geez I didn't realize > those were so cheap, I'd like an "atomic clock" too, and promptly ordered > three from three different vendors off of ebay. I figured I'd get one out > of three that showed up and worked, but I actually got all three, and all > three appear to operate. I also saw on leapsecond that many time-nuts use > the Trimble Thunderbolt as a GPSDO, and as they were cheap, I ordered one > of those from ebay as well. > > Now that I have all of these, and I've cobbled together a power supply to > power everything I hooked the Thunderbolt and the 5680's to the one piece > of test equipment I currently have - an oscilloscope. Maybe out of > ignorance I decided that the GPSDO would be the "most accurate", so I set > the trigger of the scope to the channel that the thunderbolt was connected > to. I figured the changing relative waveform phase of each unit would > give me idea of how in line each unit was at a gross level. > > To my delight the GPSDO and one 5680 is very close, and the relative phase > of the GPSDO and that unit remain relatively constant. Two of the other > units are "off", and I'm curious as to why. Each of the "off" units goes > in and out of phase with the GPSDO (i.e., 360 degrees goes by) in about 20 > seconds, which I think is +/- 0.05Hz, which I think, is 5x10e-9 at 10MHz > (correct me if I'm wrong). (All units left to "warm up" over 12 hours, > the GPSDO has clear view of the sky and self survey was completed, etc.) > > I've tried to do a bit of research on Rubidium aging, which seems to cause > the oscillator to slow over time ( > http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA485423) when exposed to air > (helium), so I expect the 10 years or so of service would make sense > assuming about 5*10e-11 a month, over that period of time. I presume > that's what the DDS in the unit is there for to allow the units to be > corrected for aging ( > > http://www.ko4bb.com/Manuals/05%29_GPS_Timing/FEI/FE-5680A/FE-5680A-tuning.p > df) > > > So I guess my questions are: > Does my line of reasoning make sense? > Should the GPSDO, for lack of a better standard, over the "eyeball averaged > over 20 seconds" be the best frequency source? > > > As someone just getting into this, feel free to tell me to go do my > homework and point me at a link! I just wanted to make sure I was on the > right path of discovery. > > Thanks, > Don Barr KA2YDX > > > > > > > <[email protected]> > _______________________________________________ > 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.
