From: "Stephan Sandenbergh" <stephan@rrsg.ee.uct.ac.za> Subject: Re: [time-nuts] Dithering vs. locking all the clocks to the OCXO? Date: Tue, 4 Jul 2006 23:33:39 +0200 Message-ID: <ca708d410607041433x1f26d225l90063b96cfe6a05d@mail.gmail.com> > >On 7/4/06, Magnus Danielson <cfmd@bredband.net> wrote: > > >Actually, for these distances, pulling some fibre and do two-way time transfer > >should not be too hard. Acheiving sub-nanosecond relative timing should not at > >all be unfeasable but should rather be consider fairly easy. > > Do you mean easy for fibre or for a GPSDO? With the fibre-based two-way time transfer. For shorter distances you can do well on coax, but for the distance range you require you really want to go fibre. That world is a bit different but can be made sense off. Cheers, Magnus

Hi Stan, perhaps you can construct yourself something similar to this http://www.kuhne-electronic.de/english/special.htm Choose "Chrystal heater" from the menu on the left Regards Ulrich Bangert > -----Ursprüngliche Nachricht----- > Von: time-nuts-bounces@febo.com > [mailto:time-nuts-bounces@febo.com] Im Auftrag von Stan Searing > Gesendet: Dienstag, 4. Juli 2006 18:53 > An: 'Discussion of precise time and frequency measurement' > Betreff: [time-nuts] questions on uncompensated crystal oscillators > > > Hello, > Please excuse the fact that this is not what we all > consider precise frequency. I am selecting crystals to use > for a medium to high volume application. > The basic criterion are: > - used with a VLSI inverter based oscillator with > 3.3 V supply, but somewhat high impedance output. > - frequency: 27.000 MHz fundamental within 40 (or so) ppm over > temperature including 7 to 10 years of aging. > - HC49S case > - no production line trimming > - low cost > > After looking at the design issues, I wonder if some of you > haven't faced similar designs and have some suggestions > regarding the following issues: > > - Is there a free (or inexpensive) spice that works well > simulating crystal oscillators? > (I did see the submissions to this email list last September > on LTSpice.) > (I have tried using the SIMetrix Intro package, > and it generally seems to produce good results, > but I found it's awkward or impossible to measure > frequency to lots of precision (taking an FFT helps), > and some results regarding oscillator frequency > shifts as a result of small delay changes in the > inverter seemed questionable to me.) > > - Are there some good papers dealing with the practical aspects of: > - transforming the Q limiting element of the design from > a series R to a parallel R > - Rs vs. ESR > - exceeding the correlation drive level of a crystal > - measuring the drive level & calculating the maximum drive level > - negative R and oscillator startup margin > - consumer video color subcarrier tolerance > > - Do you have any suggested suppliers for crystals with the > following specifications: > - HC49S > - 27.000 MHz > - 10 ppm tolerance > - 10 ppm stability > - 18 pF load > - trim sensitivity less than 15 ppm/pF > - 7 (or better yet 10) year aging less than 10 ppm > - drive level up to 1 mW (may not need to be this high if > the ESR is < 30 ohms or I better understand our maximum > inverter output voltage) > > If someone is interested in providing comments on the app > note I'm working on, that would also be appreciated. > > Thanks > Stan Searing > > > > _______________________________________________ > time-nuts mailing list > time-nuts@febo.com > https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts >