On Wed, Feb 24, 2016 at 6:22 AM, Neil Green <[email protected]> wrote:
> > What would be my next step up be, hardware-wise, in terms of improving > precision, stability, etc? A GPSDO? Budget is limited as far as these things > go - about £150 UK/$210 US. Given that you already have the GPS and PPS, you can build your own GPSDO for very little cost. The most expensive part is the crystal and as long as you are not going for top of the line performance a cheaper crystal will do. (You asked about the NEXT step not the LAST step) A simple GPSDO is, well, simple. All you do is compare the phase of the PPS to the phase of the 10MHz crystal and then adjust the frequency of the crystal to keep the phase difference constant. Can be done all in software by a $2 micro controller chip. By Time Nut standards the performance will not be top notch but compared to your NTP server it could literally be 10,000 times better A while back I tried to build the cheapest and simplest GPSDO possible and except for the price of the crystal and GPS receiver I spent about $5. Performan ce was such that when I put the cheap GPSDO 10MHz output and my Thunderbolt both on a dual trace scope I could see some movement in phase over hours long time but over days in stays locked First divide the 10MHz crystal to say about 1Mhz using a TTL divider. Some (most) micro processor chips have a way that an external signal can trap the current value of a counter. Let both the PPS and the 1Mhz do this and look at the difference in counts. Adjust the crystal so the difference remains constant. Don't worry about details, that is for latter make it as simple as possible. Improvement is for version #2. The next step up would be something like the Thunderbolt or a much better DIY GPSDO. -- Chris Albertson Redondo Beach, California _______________________________________________ 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.
