[time-nuts] Thunderbolt? (re simple gpsdo.)

Chris Albertson albertson.chris at gmail.com
Sat Dec 31 15:34:14 EST 2011

I think this is the simplest design that can still work, just one flip
flop, divider and a capacitor.

What level of performance did you get?    I think it depends on how big the
integrating capacitor is and how stable the VCXO is.   I guess if you
switched to using the t-bolt the performance was not as good as a t-bolt.

On Sat, Dec 31, 2011 at 10:23 AM, WarrenS <warrensjmail-one at yahoo.com>wrote:

> Chris
> Here is a GPSDO I built that better fits Your definition of "Simple". I
> used this as my freq standard before getting a TBolt.
> 1) Feed the PPS output of an oncore GPS timing engine which has 1 Hz or
> better yet 100 Hz output to the clk of a D FlipFlop (74HC74)
> 2) Feed the FF's D from a 10 MHz osc which has been divided down to 100KHz
> or less using 74HC390.
> The FF output shows if the Phase of the Osc is greater or less than the
> GPS signal and the FF will toggle back and forth when the phases are near
> equal due to the typical 40 ns jitter on the GPS pulse signal.
> 3) Add a RC filter to the FF output using a big cap, so the voltage out of
> the RC filter is 0 to 5 volts depending on the duty cycle of the FF.
> (A small R in series with the cap will help stabilize it if a real Big cap
> is used).
> 4) Feed the filtered analog FF output voltage (No buffering necessary) to
> the EFC of an 10 MHz osc that has its EFC input desensitized with a couple
> of Rs and has been set to be real near 10 MHz at the nominal analog FF's
> 2.5 volts output using the Osc's mechanical tuning and/or add a fine freq
> adj pot.......

Chris Albertson
Redondo Beach, California

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