[time-nuts] Re: building a frequency counter.. use 1PPS, ,or 10 MHz reference from GPS?

[Tom Van Baak]

 > For a time base, I'd like to use a 1PPS pulse from a GPS, but how 
accurate are they?

A GPS pulse is plenty good enough for your project. You want to count 
cycles of a frequency up to 100 MHz, and 100 Hz resolution "will be 
fine". That's very easy because you're asking for only 6 digit, or 1 ppm 
resolution and precision.

No need for a GPSDO. No need for FPGA. A microcontroller would work, but 
yes, you can do this with counters and gates if you want to keep it 
simple, or retro. Three 'HC390 decade counters will give you 6 digits. 
You'll have to come up with something for the first digit since 100 MHz 
is too fast (or just use a larger prescaler). Use the GPS/1PPS for the 
start/stop gate. That's all you need for a basic 6-digit counter.

Add a 4th 'HC390 to extend to 7 or 8 digits if you want. It's only when 
you get to 9 or 10 or 11 or 12 digit counters that things get 
complicated. But for your stated goals, a simple GPS/1PPS 1-second gated 
counter should work fine. Sounds like fun project.

/tvb