There are special "wide-pull-range" VCXO's where a 10MHz unit will indeed have sensitivity of 600Hz/V or more. e.g. http://www5.epsondevice.com/en/products/vcxo_standard/vg4231ca.html
I don't know exactly what Epson does inside that particular unit, but a trick to get wide pull range with discrete circuits is to put two or more crystals in parallel. Tim N3QE On Wed, Sep 14, 2016 at 4:40 AM, Lars Walenius <lars.walen...@hotmail.com> wrote: > The VCXO sensitivity given is strange as it indicates a far to wide span > so I guessed 30ppm and if it is higher it still needs the damping from > R2-C2. > For the OCXO I used the figures given. With 2Hz per volt and 8 Volt span > you have 16Hz of span. 16Hz divided with 10MHz is 1.6ppm (parts per > million) can also be said as 1.6us/s. > > Lars > > >From: Bryan _<mailto:bpl...@outlook.com> > Sent: den 14 september 2016 03:59 > > >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: lars.walen...@hotmail.com > > To: time-nuts@febo.com > > 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:bpl...@outlook.com> > > >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: wb6...@cox.net > > > To: time-nuts@febo.com > > > 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 -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.