Yes indeed I used the GPSDO to do exactly that. When I play with the synthesizer things go all over the place. As someone pointed out a long time ago, the synthesizer doesn't behave as you may think. Logically I had believed that a LSD of 1 change would be some simple shift. But it seems that was wrong. What I am looking at may be a drift thats far smaller the 1 LSD. I can't really tell. Regards
On Sat, Dec 6, 2014 at 11:22 AM, Magnus Danielson < [email protected]> wrote: > Paul, > > On 12/06/2014 04:51 PM, paul swed wrote: > >> Magnus >> Great but I am looking for very specific detail. If you pick a wrong peak >> especially if you can't see peaks on a very weak tube then I think that >> translates into an actual offset. >> > > Yes, there will be a significant offset unless you adjust your synthesizer > frequency accordingly, which few clocks allow you to do. > > Then, if you have a weak tube, then the center pidestal is the most likely > to lock onto. > > If thats a true statement. Given the modern GPS boxes we have today that >> are stable. Wouldn't you see that as a always constant drift. Say 7-10ns >> over 20 minutes? >> > > It would be significant yes, and it depends on the C-field, but in > general, the C-field is so strong as it separates of the -3, -2, -1, +1, +2 > and +3 peaks from the central 0 peak so that it can be observed without > interference. The C-field will offset the 0 peak un a much lower degree > than it offsets the closer -1 and +1 peaks (which is also weaker). The > nominal C-field setting is reflected in the synthesizer offset and balances > out. That way most cesiums isn't really as "primary" as being advertized. > > If you restart the system it magically comes back to the same offset. >> Also there is a second harmonic reading and control. If you very the fine >> phase on the 5 MHz indeed the ctl voltage readout adjusts and the system >> is >> locked. Green light. >> > > It is actually the strength of the 1st harmonic which is interesting, > since if you have strong 2nd degree with almost zero 1st degree, then you > are pretty much on the mark (i.e. lock). > > Here is the real issue the tube has always been so weak that you simply >> can't look at the i meter and see humps. What I had done a long time ago >> was add in another meter that was very sensitive and then use a magnifying >> glass to see the peaks. >> > > I wired up a network analyzer with a mixer to re-modulate the response > onto the 12.6 MHz signal. Worked like a charm, but slow scanning rate is > recommended. I think I did some photos of that. > > Anyway, on a weak tube, you are most likely to lock to the 0 pedistal, > because it is the strongest of all 7. If you have a GPSDO you can pre-tune > your OCXO to help locking. > > Cheers, > Magnus > > > >> Regards >> Paul >> WB8TSL >> >> On Sat, Dec 6, 2014 at 10:41 AM, Magnus Danielson < >> [email protected]> wrote: >> >> Hi Paul and Bob >>> >>> On 12/06/2014 04:04 PM, Bob Camp wrote: >>> >>> Hi >>>> >>>> Sure you can set them on the wrong peak. If you really get confused, you >>>> can also set them on the wrong transition … (gulp). >>>> >>>> Peak wise, the one you want is the highest Q / best SNR. Set it to one >>>> of >>>> the others and your ADEV degrades. >>>> >>>> Transition wise … not a good idea at all. >>>> >>>> >>> It's worse than that. Of the 7 peaks, the middle one has significantly >>> least sensitivity to the C-field, as well as having the strongest >>> response. >>> >>> The "new" digital cesiums actually measures the near-by peaks to sense >>> the >>> C-field and servo the C-field and then use the center peak for servo the >>> frequency. This is a key to increase the stability of frequency and >>> reduce >>> a systematic effect. >>> >>> Cheers, >>> Magnus >>> >>> >>> Bob >>> >>>> >>>> On Dec 6, 2014, at 9:11 AM, paul swed <[email protected]> wrote: >>>> >>>>> >>>>> I have a curious question that really applies to all Cs references. >>>>> Its possible to set them on to the wrong peak. >>>>> Typically in the literature it will speak to at least 3 peaks and you >>>>> want >>>>> to select the highest central peak. >>>>> However if you select the wrong peak, how much would the output >>>>> frequency >>>>> be off? >>>>> I had read a tech note for the airforce that seems to indicate its >>>>> pretty >>>>> easy to get on to the wrong peak. >>>>> Regards >>>>> Paul >>>>> WB8TSL >>>>> _______________________________________________ >>>>> 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. > _______________________________________________ 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.
