Bruce, 2008/10/24 Bruce Griffiths <[EMAIL PROTECTED]>: > You've missed a vital point: > There is no RF output from the rubidium cell itself at all. > It doesn't oscillate as does an active hydrogen maser.
Thanks for putting me right on this, I obviously need to study this more. So as I see it, a CPU measures the output of the rubidium lamp and tunes a signal source which is used to excite the lamp to give the highest output. The output of the signal source is used to discipline a 10MHz ocxo and the output of this becomes our reference standard. Well, we are at the mercy of the xtal oscillator, if it jumps, so does the output, straight away, and it does not matter how good our high Q rb standard is as there will be a jump which should be corrected by the feedback circuit, IE. the output of the ru lamp photo detector will go down and the cpu will have to correct it causing the oxco to be corrected again. How long this takes is down to the time constand of the feedback mechanism. OK, even given this setup, would it not be possible to remove the ocxo from the loop and just use the cpu to control a non-xtal'd signal source rb exciter. The output of this signal source could then be divided down to 10MHz and filtered. I appreciate that using a rb exciter that is not disciplined would not be as stable but with good design this can be mitigated and, once the signal generator is on frequency it should be possible to keep it that way with the optical feedback to the cpu without a lot of noise from the cpu hunting for the photo detector peak. After all, in the ocxo design, this is also being varied by the cpu and can be kept stable so why not the rb exciter oscillator as well. 73 - Steve -- Steve Rooke - ZL3TUV & G8KVD Omnium finis imminet _______________________________________________ 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.
