Hal Murray wrote: > You want 66.6666 MHz from 10 MHz. > > I can think of several approaches. > > 1) Patch the radio stuff to work with 10 MHz. Since 10 MHz is common from > things like GPSDOs or Telco surplus rubidium clocks, somebody may have done > that already. > > 2) Build a PLL. The first step is probably to find a 66.666 MHz oscillator > that has an external fine tuning pin. Then it's divide by 20 and 3, compare, > filter... > > 3) Get to 66.666 MHz by dividing by 3 then multiplying by 2 and 5. I don't > know much about this area, but there was a lot of discussion here a few > months ago. Check the archives. >
Actually need to multiply 3.333.. MHz by 20 (5 x 2 x 2) No need to multiply by 2 or 4, if the output of the divide by 3 is a 1/3 duty cycle square wave, one can extract the 2nd (or 4th) harmonic of the square wave repetition rate with a filter. Amplify and multiply by 5 (can use the same approach as used in the 5370A/B frequency multiplier chain (1 transistor per multiplier) and filter. A high level injection locked divider can have lower close in phase noise than a digital one. > 4) Use a DDS chip to synthesize 66.666 MHz. Analog Devices makes lots of > nice ones. One problem with DDSes is that they normally make spurs. But > they aren't a problem if the target frequency is a clean multiple of the > source frequency. 20/3 doesn't sound clean, but I'd have to do a lot of work > to check the details. There may be a clean frequency that is close enough to > 66.666 MHz and/or one that has spurs that are far enough out so you can > filter them. > > 5) Use a low cost 66.666 MHz oscillator and live with the error. You may be > able to correct any errors. The key step would be to feed the 66.666 MHz to > a counter running off the T-Bolt clock so you know the real frequency of your > 66.666 MHz osc. Suppose your 66.666 MHz is 73 ppm fast and you want to > listen to 12.123 MHz. You would set the radio to listen to 73 PPM below > 12.123 MHz. > > > > Bruce _______________________________________________ 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.
