On Mar 7, 2:17 pm, Sunish Issac <[email protected]> wrote:
> Longtime back I had tried using the watch crystal, but good accuracy can be > obtained only if the PCB is done well taking care of the capacitance. > > Sunish > Actually watch crystals are calibrated/cut assuming near body temperature for operation (Human oven!). Also you need an adjustable trimmer capacitor. Even using the main clock 4MHz to 20MHz crystal you really need adjustment for decent frequency measurement or time keeping, simplest is an adjustable trimmer capacitor and a "PTC" thermistor mounted against crystal. Next level is to use a TCXO module (with trimmer pot adjusted) instead of crystal. Use a GPS conditioned Oven crystal to calibrate. I had loan of test gear and used it to calibrate a 10MHz Oven crystal. I fed both to X & Y inputs on a scope and set gain so as to have an oval. When the oval is not rotating at all the frequency is the same. If one is x2 the shape is stationary figure of eight. You can't do this on most digital scopes. -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
