Ulrich Bangert wrote: > Bruce, > > thank you for correcting me. Here I have clearly fooled myself. However > your posting originated some new ideas: With the GCD becoming THAT low > an analogue phase lock to a 10 MHz reference will not be easy. But if we > stop to think about phase locked VCXOs we need not bother anymore about > odd exotic xtal frequencies Yes you would need a VCXO with low close in phase noise for the 17.73447MHz source. That crystal frequency isnt too exotic as RS components have suitable crystals, if you build your own VCXO. > at all that may generate us a GCD of 10. > Instead we are free to choose for example 10000010 Hz for the > controller's frequency. Which brings us back to a construction of a good > offset generator. > > Until now I have believed that a good (low phase noise, high stability) > offset generator would involve > > a) a number of single sideband mixers (as described in > www.horology.jpl.nasa.gov/papers/fssa.pdf) > > or > > b) the well known offset synthesizer circuitry as described by Rick > Karlquist. > > I am sure that both ideas work excellent, although I am unsure whether > a) can generate an 10 Hz offset. However, both methods involve circuitry > that I would not call exactly "quick and dirty" and their use would > overstress the try to make something really simple. On a new internet > search for "offset generator" I came over this one: > > 10Hz offset by method a is trivial (9.99999MHz is just as useful as 10.00001MHz):
1) Use a LSB mixer to mix 10MHz with 10MHz/1000 to generate 9.99MHz 2) Bandpass filter this and then use a USB mixer to mix 9.99MHz with 9.99MHz/1000 to generate 9.99999MHz. 3) Use a PLL to phase lock a low noise VCXO (spare 10811A or similar detuned mechanically by 10Hz??) to the 9.99999MHz output to remove spurs etc. Even a DDS followed by a PLL cleanup loop (10811 plus analog PD etc.) should work well although with a binary tuning word obtaining an exact 10.00001MHz (or alternatively 9.99999 MHz) output isnt possible. A DDS has some advantages over a synthesizer using dividers in that additional noise isnt aliased into the output. > www.diva-portal.org/diva/getDocument?urn_nbn_se_liu_diva-1838-1__fulltex > t.pdf > > What do you think about that topology? Let the "IF in" be the needed > offset and the "offset OSC" be our 10 MHz reference. Would that not make > an really easy way to generate an precise offset with the wanted > features? > > Not much (can work well with 20kHz offset but not with 10Hz offset), direct generation mixing 10Hz with 10MHz like this requires a rather low PLL bandwidth. Also filtering out the unwanted sideband may be problematic. > Best regards > Ulrich Bangert > > Bruce _______________________________________________ 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.