-------- In message <[email protected]>, Magnus Danielson writes:
>Consider for instance that we have a LPRO rubidium and we want to use a >clean-up oscillator to provide better phase-noise, what would be a good >selection? There are special devices for this, like Vectrons TRU-50, but they are hard to get hold of. I have an item far down my todo-list simply labeled "Inverse PPSDIV": For not relevant reasons I once put an AMD Opteron CPU into a two instruction-loop and monitored an address line with a 'scope and that was a _very_ clean signal. In high speed digital chips, like high-end CPUs, close in phase-noise is a, if not the most, serious limitation on clock rate. The DEC Alpha silicon pioneered the use of a SAW resonator at the pointy end of the PLL, but I'm not quite sure what they do today. The TODO point is to take a RaspBerry Pi, run a tight loop with all which wiggles a GPIO pin with all interrupts disabled, and measure the phase noise. It's going to wander all over the place, because it comes up from a 1 cent Xtal, but the phase noise will be from the on-chip resonator, whatever that is. If it's any good, buy a Pi-Zero, rip out the X-tal and feed it from your LPRO instead. If you only need one GPIO pin, I doubt the exact clock frequency matters much. (The BeagleBone is interesting too, since the PRU units run autonomously at 200 MHz from their own memory, so the main CPU could do other jobs for you.) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
