Working on the wwvb remodulator and have learned a fair amount about tuning fork crystals. there is a fair amount of information out there. It seems generally the same thing and as it turned out perhaps not all that useful. This is what I have done a schematic in words. Using a single 74hc14 inverter feeding a buffer inverter pins 3 and 4 22 M feedback resistor pin 1 to 2 Xtal feed back path Pin 2 to 50K variable pot to a 68K and 100K resistor in series to 230 pf to ground. This same junction has the 60 Khz xtal feeding then back to pin 1. Power supply is a CS5206 3.3V LDO 22uf and .047uf to ground.
The 230pf cap grossly gets the system close to frequency. About 5 Hz. Adjusting the variable pot puts the xtal on frequency. Granted this is simply changing the crystal drive. But it works well. The 50K pot gives about 8 Hz adjustment range. I did indeed use small variable plastic caps. They were a pain to use actually. Granted a high quality air variable would be good and you can tell how its been adjusted. Not so with the plastic caps. You are a bit blind. I then tested 10 xtals out of 50 a random sampling. They ranged from 59.996 to 60.005 some came close to the original mouse xtal I built the system with below 1 Hz. Conclusion The 60 Khz xtals will need a way to adjust. They simply are never close. The feedback resistor has to be very large I was surprised by how large. 22 M and I could go higher. Lowering the drive raises the frequency to a point. Anything above 270-330K cause startup issues. The circuit as describes starts very quickly sub 200 ms. I will update the wwvb remodulator schematic with this information and most likely make a real schematic and also build up my own remodulator for use until I add the remodulator to the d-psk-r to create a single package. Regards Paul WB8TSL _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.