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Oscillating 3rd overtone XTAL at fundamental?
Hi.
I have spent part of the weekend trying to resonate al old CB XTAL at its fundamental frequency. The XTAL is labelled 27.125 MHz, with a fundamental of about 9.041 MHz, which falls into 18m HAM band when multiplied by two. I assume 27MHz XTALs are 3rd overtone. Since the circuitry is/will be digital, the oscillator is one gate of a 74HC14. 470ohm resistor from gate output to the parallel of 1Mohm//XTAL. 10pF and 33pF (from the junkbox) capacitors to ground on each side of the XTAL. No oscillation (I have no oscilloscope, I use my HF receiver to troubleshoot oscillators at known frequencies). If I replace the XTAL with a 10.000 MHz rock the oscillation is loud and clear. I have never built something with an overtone XTAL. I know that I need an output resonating circuit if I want to extract the 3rd harmonic. Do I need the same if I want the fundamental? Are overtone XTALs "harder" to resonate? Are those old CB XTALs 3rd overtone? I assume my 27MHz XTAL works. :-) Thanks in advance for all suggestions, Paolo IK1ZYW |
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