On Tue, Feb 19, 2013 at 11:59 AM, Jerry Flanders <jefland...@comcast.net>wrote:
> I think the most important thing to remember in the Rb vs GPSDO debate is > that without some other standard like a GPSDO or better to compare to or > calibrate against, you never know that your Rb oscillator is actually > on-freq. Sure you do. Double check it against WWV. If it is within 1/2 Hz, the Rb is locked and all is well. If it is unlocked it is very obvious because the output frequency sweeps up and down by almost 1kHz. Tune in WWV and you will KNOW it is unlocked. Once it locks and WWV is clear, it is working and nothing it going to move it off 10MHz. > The LPRO-101 has an adjustment to vary its freq. How would I know that > adjustment pot didn't get jostled during shipment? OMG, it could be .015 Hz off if it got turned all the way to the stops! Yes the tuning limit is +/- 15 MILLIHERTZ. Remember, the frequency determination is fixed by an electron transition in a shell of the Rubidium atom. Unlike a crystal oscillator, it can't be very far off. If it locks up at all, it will be within 1/2 Hz at 10MHz and quickly get better than that. > Lastly, since we know the early Rb units were subject to failure due to > aging of the Rb tube, how would I know the one I was considering has much > life remaining ? > Measure the lamp voltage. It is a pin on the connector. More than 7.5V and it still has lots of life left. > > Bottom line - I would HAVE to be able to check/calibrate it, but against > what primary reference? > And that is the point. You don't. Sure if you want to get it within 1 mHz you could tweak it but even without any calibration max it could be off after warmup is less that 1/100 of a Hz. Without a GPSDO to compare the Rb to, I think buying a Rb one would be a > crap-shoot. After thinking it through, I skipped the Rb step and went > straight to the GPSDO. > But the GPSDO can be farther off during periods of poor GPS constellation geometry. Bottom line: it pays to understand the technology. -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
