[time-nuts] wwvb 60 khz tuning fork crystals Some insights
ed breya
eb at telight.com
Thu Jun 27 00:13:15 EDT 2013
I presume you used the regular 74HC04 or 74HCU04 inverter, not the
74HC14 Schmitt trigger input type?? If the '14 is actually used, that
may explain the problems around setting the feedback biasing resistor
value - you may be overriding the built-in hysteresis to get it in
the linear region. Usually that R isn't very critical with regular
crystals, but maybe tuning fork types need more gain, or, if it's
actually a '14, the input impedance is probably lower than a regular
gate, so it's loading the resonator.
Ed
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