Hi Anything under 100 ppb relative to WWVB is probably closer than the ionosphere will let you get under normal conditions. You can indeed get a zero beat, but that's not always a guarantee that the carrier isn't moving around at some odd rate. Far better to use WWVB. The LF path is much more predictable, so you can pick "good" times to check it each day. After a few days you can have some pretty good information.
Bob On Sep 27, 2013, at 4:26 PM, Bob Albert <bob91...@yahoo.com> wrote: > I just did what I consider to be the best calibration possible without > getting more equipment. I adjusted my generator to be within 0.25 Hz of 15 > MHz WWV. Then I matched my counter to the generator at 520 MHz, within about > 2 or 3 Hz. I am satisfied that nobody is going to call me out of tune. > > I am impressed with the ease of working with this gear, both units HP but > decades old. > > > Thanks for your help. If I get a GPS or rubidium unit I will take it > farther. (The GPS units require antennas and connectors I don't have, plus > software and computer interface, too much trouble right now.) > > Bob > > ________________________________ > From: Bob Camp <li...@rtty.us> > To: Discussion of precise time and frequency measurement <time-nuts@febo.com> > Sent: Friday, September 27, 2013 1:11 PM > Subject: Re: [time-nuts] Shielding a DAC line -> WWV > > > Hi > > If you already know that the standard is within 50 ppb, then it only can > drift 50 nanoseconds per second. If you check it every 100,000 seconds (a bit > more than a day), it can not have slipped more than 5,000,000 nanoseconds. > You still will be within 0.005 ms of the time tick. Even after 20 days > there's no real ambiguity relative to the tick. > > All you do is to put the audio from WWV up on a 'scope and trigger off of the > tick from your OCXO. As the tone moves back and forth on the screen you can > estimate what's going on. You need to do it same time each day and try to > avoid sunrise / sunset issues. You want as consistent a propagation path as > possible between you and the transmitter. > > Bob > > On Sep 27, 2013, at 11:58 AM, Bob Albert <bob91...@yahoo.com> wrote: > >> Ah that time tick idea makes sense. Now I just have to figure out how to >> generate it from my time base. And of course, since I don't want to stay >> awake for several days, I am worried about missing counts on the comparison. >> Did that move up, or down? And I would need to control which part of the >> cycle to compare so that I can listen to the ticks trying to be in >> synchronization. >> >> >> Bob >> >> >> >> ________________________________ >> From: Bob Camp <li...@rtty.us> >> To: Discussion of precise time and frequency measurement >> <time-nuts@febo.com> >> Sent: Friday, September 27, 2013 4:30 AM >> Subject: Re: [time-nuts] Shielding a DAC line -> WWV >> >> >> Hi >> >> One hertz at 20 MHz is indeed 50 ppb. On a practical basis, that's as close >> as you are likely to get in terms of carrier accuracy over HF radio. >> >> To do better, you would need to go to the time domain. Generate a tick off >> of your oscillator(s) and compare it to the time tick on the radio. Compared >> over a time span of days you can improve your accuracy. >> >> Bob >> >> On Sep 26, 2013, at 9:24 PM, Bob Albert <bob91...@yahoo.com> wrote: >> >>> This is off topic but I'm unsure how to do it properly. >>> >>> I am trying to 'discipline' a couple of sources. I zero beat with 20 MHz >>> WWV but can't tell the difference between fading and the beat, so I am >>> stuck in the vicinity of 1 Hz possible error. That's 50 ppb I think. >>> >>> What can I do to take the next step to bring the oscillators in closer >>> agreement? I am not ready to go GPS or buy a rubidium standard. >>> >>> >>> Bob >>> >>> >>> >>> ________________________________ >>> From: Bob Stewart <b...@evoria.net> >>> To: Discussion of precise time and frequency measurement >>> <time-nuts@febo.com> >>> Sent: Thursday, September 26, 2013 6:13 PM >>> Subject: Re: [time-nuts] Shielding a DAC line >>> >>> >>> Hi Bob, >>> >>> I should have mentioned that I added a new 5MHz output, and the coax ran >>> within 1/8" of the single DAC wire going to the OCXO. I don't think >>> anything else changed, but of course there could be some flake of something >>> on the DAC line that I missed. I put on the RG-174 and I see that it's >>> still locking high. I suppose it could be just that it was a long power >>> cycle to the oscillator. Come to think of it, this thing does like to move >>> to a new voltage sometimes when I have it off to mess with something. So, >>> maybe it's just the oscillator being cranky. I haven't had it off for more >>> than just a few seconds in a long time. If I weren't in test and >>> development mode where anomalies are good, I think I'd put the old one back >>> in. >>> >>> Thanks as always, >>> >>> Bob >>> >>> >>> >>> >>> >>>> ________________________________ >>>> From: Bob Camp <li...@rtty.us> >>>> To: Discussion of precise time and frequency measurement >>>> <time-nuts@febo.com> >>>> Sent: Thursday, September 26, 2013 7:54 PM >>>> Subject: Re: [time-nuts] Shielding a DAC line >>>> >>>> >>>> Hi >>>> >>>> I suspect that you have a ground offset between the OCXO's ground return >>>> and the DAC's ground reference. The signal *should* be DC, Shielding it >>>> won't hurt, but it really should not help much. If anything is an issue a >>>> simple R/C filter at the OCXO pin should nuke it better than coax will. >>>> >>>> Bob >>>> >>>> On Sep 26, 2013, at 8:09 PM, Bob Stewart <b...@evoria.net> wrote: >>>> >>>>> I made some minor hardware changes to my GPSDO today and I see that it's >>>>> locked to a new DAC voltage about 21mV higher. So, I was wondering about >>>>> shielding the short run to the OCXO. I have immediately available RG-174 >>>>> and I'm putting that in. But, should this be some sort of steel shelled >>>>> semi-rigid coax? Maybe it's a dumb question, but I thought I'd ask. >>>>> >>>>> Bob - AE6RV >>>>> _______________________________________________ >>>>> 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. >> >> _______________________________________________ >> 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. _______________________________________________ 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.
