Hi, I have a plan which involves the dividing down of the 10MHz of a GPSDO and a rubidium (LPRO) to about 1MHz or 100kHZ and applying them to a XOR or D latch to get a PWM signal that can be averaged for a strip chart recorder or 12 bit analogue data logger. The DC output gives a range of 5 volts for one microsecond or 10 microseconds phase difference and folds back if this difference is exceeded. The data from the datalogger is in a format that a spreadsheet can use. With time and phase measurements I wonder how hard it is to get Allen variance. I realise the PWM method requires a low pass filter and this will prevent short period variances from being calculated. cheers, Neville Michie
On 09/11/2008, at 8:43 AM, Alan Melia wrote: > This is an interesting thread again.....it may be similar to ones > that have > been discussed, but one or two furthur questions occur to me. I have a > Montronics sytem that does comparisons by the multiply and mix > process, and > I find (also common to more modern Kethly systems) that the > limitation is > around a part in 10^10 where the noise on the phase output makes it > not > really usable (without a lot of averaging) being around or in > excess of 90 > degreees even with a couple of very good OXCOs. How does the 10G > comparision > avoid this problem with standard multipliers? I doubt you can go > all that > way with low-noise multipliers and have any useful signal left, or > have I > missed something. At present I use a phase meter (lock in amps can > be quite > good) at the MHz range and datalog the phase drift for several > hours. I have > determined that setting "on the nose" is not necessary (for my > applications). It is more useful to know how far a source is "off". > How does the mix down compare with the seemingly more popular "mix > down and > timestamp" I understand from previous threads that this has more > potential > but might it also be as good even using simpler circuits that the NIST > system. > > Thanks for all your efforts inthe background John..... great reading > material ! > > Alan G3NYK > > ----- Original Message ----- > From: "Jeffrey Pawlan" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]>; "Discussion of precise time and frequency > measurement" <[email protected]> > Sent: Saturday, November 08, 2008 6:40 PM > Subject: Re: [time-nuts] Checking accuracy of Rubidium standards > > >> >> >> On Sat, 8 Nov 2008, Randy wrote: >> >>> I was wondering if it is worthwhile or even feasible to compare >>> an LPRO >>> Rubidium standard against a Z3801. Since their frequencies are >>> probably >>> going to be extremely close anyway it would seem some special >>> method/equipment would be required for high precision. Suggestions? >>> >>> >>> Randy, W7HR >>> Port Orchard, WA >> >> The best way would be to compare the highest possible frequencies >> you can >> generate with these two sources. I use two 10GHz sources that are >> each > phase >> locked to an external 10MHz reference. Then the 10GHz outputs can be > compared >> using either of these easy methods: >> 1) look at the DC/IF output of a microwave mixer where the LO and >> RF ports > are >> driven by the two 10GHz sources. Don't overdrive the RF input to a >> level > that >> can burn out your mixer. >> >> 2) use a good microwave frequency counter to read one of the 10GHz >> outputs > while >> driving the counter's 10MHz ext ref input with the 10MHz from the >> other > 10MHz >> source. This is very fast but will only give you accuracy readings >> that > are a >> function of the resolution of the counter plus the bounce of the last > digit >> owing to sampling and triggering. >> >> 3) if you have access to a lab with one or two microwave synthesized > signal >> generators, then you can apply the 10MHz sources to the ext ref >> inputs of > each >> of these signal generators and then proceed as in 1) or 2) >> I have done comparison at 26GHz this way so I have a bit more >> resolution. >> >> 73, >> >> Jeffrey Pawlan WA6KBL >> >> >> _______________________________________________ >> 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.
