Can't quite tell from your description what your circuit is, but if I recall
correctly back when i was doing hardware design a crystal oscillator using
logic gates required two gates. I used to use three---two for the
oscillator and the third for a buffer.

The two inverters where tied together with a capacitor between them. Then
the crystal was placed from the input of the first gate to the output of the
second. The output of the second also went to the buffer stage.


!-----------------crystal------------|
Like this: - gate one---capacitor---gate two---gate three---circuit
output

As I recall, there was also a resistor from the input of gate one to ground,
and from the output of gate two to ground.

I do not recall the capacitor or resistor values, but when properly built
this circuit never failed to oscillate with any crystal within the range of
the gates (fundamental mode only).

Jim
N8EE
"PaoloC" wrote in message
...
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