GPS Locked Frequency Standard Circuit Diagram

Imagine that one day you wake up to learn that all the GPS satellites have been destroyed. What's happening? War? Super-massive solar flare? Whatever it is you probably won't be spending the afternoon in your electronics hobby area. In all my years of playing with GPS it has never been "off the air." So, as a hobbyist, do you really need a GPS standard with "hold-over" that learns the properties of your oscillator and corrects the oscillator even when GPS is not present? (Hint: nope.) So why spend an inordinate amount of time and effort giving your standard a hold-over function you can only appreciate by physically disconnecting the GPS antenna?

This unit provides an excellent 10 MHz reference as long as an accurate 1PPs is supplied by the GPS receiver. When GPS goes down you should be brushing up on your hunter-gatherer skills anyway.

This simple frequency standard uses the 1PPS available from many GPS receivers to lock a stable oven-controlled oscillator, holding a few hundred uHz of accuracy from moment to moment depending on the quality of the oscillator. (My old "Small Fry" wanders under +- 2 x 10-11.) It's a "nearly" analog circuit using three logic chips to perform simple tasks and a third-order phase-locked loop realized with two op-amps. The PLL behaves as though the lock frequency is 1 MHz due to the sampling technique (albeit updated only once per second) so the phase sensitivity is about 1 million times higher than if the phase comparison were done at 1 Hz. Read more click here


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