Hi Assuming you are after a reference at 10 ppb accuracy:
10 ppb would be a 10 second beat note on WWV at 10 MHz. (I *hope* I got the decimal point right that time). Fire up your radio and start listening to the various frequencies. You want a time when it’s crystal clear with absolutely no fade. Yes you will wait a while to do that. Pad down your reference and do a good zero beat. Observe it for at least 10 minutes. Come back another day and check it again. You may / may not actually have 10 ppb doing this, but you will be pretty close. It assumes you have a radio, antennas, time, and a way to zero beat at more than one frequency. If you are stuck at 10 MHz it will take more time …. ——— A GPSDO will run you far less than the cost of all the gear you already have for the WWV zero beat. It also will not involve a few weeks of your time checking for a good set of band conditions. Finally it will give you a reference that is at least 10X better than your target. If you intend to *set* stuff to 10 ppb then the reference needs to be 1 ppb…. The other assumption above is that your existing reference is stable to much better than 10 ppb. If it’s not, then you need both a reference and a way to calibrate it. The GPSDO would give you both, since it’s got a 10 MHz OCXO built into it. Bob On Mar 2, 2014, at 1:48 AM, Bob Albert <[email protected]> wrote: > Chris, > > Okay you want numbers. Well, I think 10 ppb or thereabouts should do it. > Somewhere there is a discontinuity in accuracy plotted against cost and I > don't want to cross that barrier just yet. If I can get 1 ppb without a big > increase in cost, I'll take that. > > My need for this is nonexistent. I am only interested in doing it for the > fun of seeing all zeros on the counter and having it give me that repeatedly. > The pleasure of knowing I am as close as the equipment is capable is what I > seek. > > I'm sure many time nuts feel the same. I am not interested in offering a > calibration service or tracking spacecraft or measuring the diameter of the > moon. How do I get accurate frequency from GPS? > > > I have the same fetish regarding components, resistors and capacitors and > inductors. I have lots of good meters but am always looking for a better > one. I am trying to get six useful digits of voltage and resistance > measurement and eventually want to do it with current as well. Not so sure > about temperature, mass, and force. > > > Once I get where I want to be, I'll probably go into basket weaving. > > Bob > > > > > On Sunday, March 2, 2014 5:46 AM, Chris Albertson <[email protected]> > wrote: > > On Sat, Mar 1, 2014 at 8:05 PM, Bob Albert <[email protected]> wrote: >> Paul, as I said I just want to know how close my crystals are and be able to >> adjust them as well as they can be. > > Don't say "as well as can be" that can get expensive and time > consuming. You need to use numbers. Say "and be able to adjust them > at the 1E-8 level." > Then you will get advice to just use WWV. But what if you need > 10,000 times better? Then use GPS After that it starts getting > harder but you still are not up to "as well as they can be." > > I admit to a few years ago using a 50 cent TTL can oscillator as my > "lab standard" The part was salvage from some junk and was good to > about 5 digits accuracy. It worked actually better than I needed. My > RF signal generator was from the 1960's with a hand turned dial to > adjust the frequency. The TTL can let me calibrate the dial. > > > >> >> >> I probably will never go rubidium (note that I qualified that) but still >> somewhere one has to decide where to set the frequency. >> >> I did WWV at 20 MHz for a beat of somewhat slower than one per second. I >> know the phase changes but probably not much in a few minutes, as the path >> length doesn't vary very quickly. And I don't need phase lock to them >> anyway. In the old days they had 25 MHz and even 30 MHz for a slight >> improvement in settability if not stability. >> >> Bob >> >> >> >> >> On Saturday, March 1, 2014 7:38 PM, Hal Murray <[email protected]> >> wrote: >> >> >>> I am trying to understand how this is done. Should I ever get a rubidium >>> standard, I'd want to check its calibration, and that's not a trivial >>> exercise. >> >> If you assume your rubidium is stable, then it's pretty easy to check and/or >> calibrate. >> >> The trick is that you need someplace to stand. A PC running ntp is good long >> term. There is a tradeoff between good and long. Good is ambiguous, but >> both how-good is your PC clock and how good/accurate a measurement do you >> want are appropriate. >> >> Probably the simplest way is to get one of tvb's preprogrammed PICs. >> http://www.leapsecond.com/pic/picdiv.htm >> http://www.leapsecond.com/pic/picpet.htm >> >> One approach is to use a picDIV to make a PPS and then monitor that. >> >> If you have Linux, you can feed the PPS to a serial port. My hack for >> counting 60Hz will work fine at 1 Hz. >> http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz.py >> >> Another approach is to use a picPET and connect a modem control signal from >> the monitoring PC to the Event input on the picPET. Then the data collection >> program grabs the time, flaps a modem control signal, grabs the time again, >> then grabs the text from the picPET and logs everything. >> >> >> >> -- >> These are my opinions. I hate spam. >> _______________________________________________ >> 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. > > > > -- > > 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.
