> On Sep 12, 2016, at 1:01 PM, Bob Camp <kb...@n1k.org> wrote: > > Hi > > The noise performance of the HMC1031 close in is pretty horrible. It’s > actually *worse* than the GPS signal noise. In a normal GPSDO the idea is to > use an oscillator that is cleaner at 0.01 to 10 Hz than the GPS.
I don’t see where you get that. To generate the phase noise figures (8,9,11,12) they used a Crystek CVHD-950. I don’t think it necessarily follows that a better quality OCXO can’t do better than that, does it? > > Bob > > >> On Sep 12, 2016, at 2:41 PM, Nick Sayer via time-nuts <time-nuts@febo.com> >> wrote: >> >> I was talking with someone at AD about a question I had about one of their >> TinyDACs when they mentioned their HMC1031 chip. It looks like the ideal >> building block for a clean-up oscillator. >> >> It struck me just a touch later that the Venus838LPx-T has by default a 10 >> MHz output that’s phase locked to GPS time. It’s not good quality, but I >> wonder if it’s good enough to be the reference for this particular chip. >> They do talk about the ability to be driven by a “noisy” or "jittery” >> reference. >> >> I think I’m going to take a crack at an OH300 GPSDO based on this design >> concept. Actually, first I’m going to actually try to quantify the jitter on >> the 10 MHz output from the Venus. From the HMC1031 datasheet it appears that >> if it’s not confined to a ±3 ns corridor that the lock indicator may not >> work (or work well). That would be a bummer. >> >> I can foresee a GPSDO with the miniDIN 4 jack presenting the PPS and serial >> I/O from the GPS module and two LEDs on the front - the “FIX” LED from the >> GPS module and the lock LED from the PLL along with two BNC jacks. It would >> have some downsides. For one, I believe in the absence of GPS reception, it >> wouldn’t be able to properly hold-over at all. But it’ll be interesting to >> see if it can work as well as the micro-controller driven variant does. >> _______________________________________________ >> 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.
