Gilles what signal is that at 162KHz. A European station? Nice thats its C controlled. Regards Paul WB8TSL
On Sun, Mar 5, 2017 at 5:54 AM, Gilles Clement <[email protected]> wrote: > Hi all, > > I have been working for a "while"… on a reference oscillator disciplined > by an RF signal (162khz), Cs stabilized, but phase modulated with time > coding information. The phase modulation is quite significant : +/-1rad > 10Hz triangular shape, leading to a frequency shift of +/- 20PI (+/-6,3Hz). > Extracting the base signal was quite an interesting challenge… I tried many > options (and even a bit more…) but it was - and is still - fun... > > Long story short, the "best" combination I came up with is the following: > 1- local oscillator built around: CD4060 Collpits + 5184Khz crystal + > pulled by varactor diode + divide by 32 > 2- Phase detection with 4046 (XOR) with pp ouput voltage limited to 1 volt > (input to 10bits ADC) > 3- Filtering and VCO controlling with a PIC16F876, programmed in assembly > language, implementing a 3rd order loop (much better than second order). > Poles at 1E-5 and 1E-3, Zero at 1E-4 => 1E-10 attenuation at 10Hz (if my > maths are correct). > 4- 13 bits 20Khz PWM control of the VCO (K0=10-3 Hz/volt) with strong > filtering (two RCs in cascade) > 5- Crystal is temp controlled (NTC resistor) as well as the whole circuits > placed in a foam isolated box. > 6- ADEV measurements perfomed with HP53132A counter (high stability option > 10 ocxo HP10811) frequency input to TIMELAB through HPIB connection (I > know it's not the best setup but simple and provides tool for comparison > between trials) > > Results to date : > . « Left side » of the ADEV 0.5s: pretty flat around 1E-9 up to > tau =10s > . « right side » of ADEV 0.5s plots: reaching 3*1E-11 at tau = > 3000s > > Comment: > 6,3Hz/162kHz = 4E-5 so attenuation of 1E10 should knock it down to 4E-15 > (well below 1E-11) ? > > My questions to the respected audience: > - Can I get any better? > - Have I reached the limit of what the RF signal can provide? > (with all the perturbations encountered on the path from the transmitter > to my antenna...) > - Am I limited by the local oscillator? > - Or the measurement gear? > - Or anything else…? > > Thanks very much for your feedback, > > Gilles. > > Note: 1E-3 = 0.001 > _______________________________________________ > 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.
