Lars: Thank you very much, your explanation was very helpful. I unfortunately don't have a background in electronics other than at a hobbyist level, and really should just lurk in the back as many of the topics discussed are way above me, but I am learning <g>. So forgive this obvious and perhaps dumb question but how are you calculating the oscillator spans, you reference the VCXO at around 30ppm. I suspect this is because the VCXO has a sensitivity of 600-1000hz/v and the OCXO of 1.6ppm has a sensitivity of 2hz/v or 3.2/v at 8v. But how are you arriving at the ppm values? -=Bryan=-
> From: [email protected] > To: [email protected] > Date: Tue, 13 Sep 2016 20:44:50 +0000 > Subject: Re: [time-nuts] Jim Miller simple GPSDO > > As I have understood it the change of VCXO gain is the reason that R2-C2 can > be omitted. With the VCXO with a large span the damping is needed otherwise > it will oscillate. > > The XOR phase detector has a range of 50us with 10kHz in. The VCXO has maybe > a span of 30ppm (us/s) and with R1-C1 time constant of about 16seconds the > phase shift will be close to 180 degrees. > > With the OCXO with a span of 1.6ppm (us/s) the apparent time constant will be > about 32 (50/1.6) seconds and the 16 seconds time constant of the R1-C1 will > act more as a low pass filter at gain cross over with a phase shift much > below 90 degrees. > > Sorry for the bad explanation but what I try to say is: If the phase detector > range divided with the VCXO span is larger than the R1-C1 time constant > R2-C2 can be omitted. > > This thread on EEVblog might be interesting for those that think of using the > Miller-style GPSDO: > http://www.eevblog.com/forum/projects/my-u-blox-lea-6t-based-gpsdo-(very-scruffy-initial-breadboard-stage)/msg938013/#msg938013 > > Lars > > >From: Bryan _<mailto:[email protected]> > >Sent: den 12 september 2016 10:49 > > >Thank you for the reply. > Yes, R1/R2/C1/C2 is what I was referencing. I was not sure as the values in > the schematic are referenced when using the C-MAC (now RAKON) VCXO. Further > into the material the author switched to a Isotemp 134-10 OCXO and used a DC > amplifier to compensate for the 0-8v for the EFC, but stated that R2 and C2 > are not needed when using this OCXO. Not sure why they are omitted, is it > because of the DC amplifier or because of different specs of the OCXO? > http://www.jrmiller.demon.co.uk/projects/ministd/dcamp.gif > > -=Bryan=- > > >> Date: Mon, 12 Sep 2016 01:25:53 -0700 > > From: [email protected] > > To: [email protected] > > Subject: Re: [time-nuts] Jim Miller simple GPSDO > > > > Hi Bryan, > > > > No ! Assuming you mean R1/R2/C1/C2 of the Miller schematic, those > > values are already set for the comparison frequency (10KHz) of the PLL > > phase comparator (U2). > > > > Bill....WB6BNQ > > > > > > Bryan _ wrote: > > > > >Hello: > > >I have been following the Jim Miller simple GSDO build project at > > >http://www.jrmiller.demon.co.uk/projects/ministd/frqstd0.htm I have a > > >few OCXO's kicking around, but wondering what would the appropriate > > >components be for for R1,R2, C1, C2 to provide the PLL filter. I assume > > >the PLL filter needs to be designed to accommodate a specific oscillator > > >specifications, or maybe it doesn't really matter and can use the default > > >values in the schematic?. > > >Was also considering using a picdiv instead of the 2- 74HC390, not sure if > > >that would be an advantage or disadvantage in terms of operating > > >performance? > > >Cheers > > > > > >_______________________________________________ > > >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.
