Hi You might check how well buffered the 60 MHz is before you tap into it. It may need a bit buffering.
Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Magnus Danielson Sent: Thursday, February 09, 2012 4:29 PM To: [email protected] Subject: Re: [time-nuts] Low-Cost Rubidium Performance Hi Javier, On 02/09/2012 10:04 PM, Javier Herrero wrote: > Hello, > > El 09/02/2012 21:06, Magnus Danielson escribió: >> >> I was just thinking about that. For these more modern 5680A, just the >> Q of the resonance and the loop filter / loop bandwidth would not >> allow for so much high frequency side-bands of the DDS to pass through. > The loop filter at least should have good rejection to the 1400Hz > frequency presumed to be used for the detection... although in the phase > noise plots I've not seen a very significant spur at that frequency. Consider that it is de-modulated and then low-pass filtered. Also, it is the alternating rate and not 1400 Hz difference in DDS setting which is the key parameter here. The 1400 Hz gives a hint of the Q-value however, which seems to be lower on these than on any of my larger rubidiums, but it is maybe to be expected. >> >> The low frequency DDS variations will go through however. > Yes :) >> >> I'd expect that the DDS noise creeps onto the 10 MHz signal one way or >> another, such as the CPLD or other location where separation is poor. >> >> It would be a bit fun to hunt around and see where the noise creeps in. >> > Quite a bit. Would be helpful to see how bad is the 60MHz signal > available inside :) All those 1Hz spaced spurs (and multiples...) could > be originated by the CPLD. Hmm, picking up the 60 MHz is quite easy! I just don't have the matching connector at home. Maybe I can borrow one from work. >> It would also be fun to see what a mixer based PI-loop OCXO cleanup >> (using say a spare 10811) would do. Using a pre-filter and mixer (to >> avoid severe intermodulations) while still getting a decenting >> filtering effect. > Also... perhaps using the 60MHz instead if it is cleaner... I've a spare > 10544 and a 10811 that would love to use for cleaning up the output (but > lack of time for now to play around as much as I would like :) ) You could build a synchronous re-generative divider to divide 60 MHz into 10 MHz (and 50 MHz). It's not that much components for a low-noise divider. A re-generative divider could also produce 20 MHz and 40 MHz, where 20 MHz is useful for among other things Z12T. Cheers, Magnus _______________________________________________ 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.
