You know Nick, the loop time constant typically used with the HMC1031 loop filter is typically 5 milliseconds. I'm sure some bigger R's and C's can used for a longer time constant, and I'm sure that'll help clean up the awful 10MHz output of the Venus838LPx-T. But it is hardly what I'd call a "GPSDO".
Tim N3QE On Mon, Sep 12, 2016 at 2:41 PM, Nick Sayer via time-nuts < [email protected]> 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 -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ 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.
