#### visions_of_eden

##### Newbie level 5

Hi,

i have a problem with a simple 30.875Mhz (garage opener) crystal oscillator .

The problem is that the frequency it generates is not the expected one . On the attached schematics , if i measure the frequency using a frequency counter on "A" point i get 30.876Mhz which is correct , but on the other side of the 27pF capacitor at "B" only get 20.606Mhz .

My crystal is a 3rd overtone crystal , is it possible that it's oscillating at 2nd overtone frequency ? Why do i get a lower frequency on the capacitor ?

The output of my oscillator will be fed into a ASK modulator , so the capacitor is only needed to cut DC offset from next modulator stage . Why does it cut the frequency ?

Maybe the oscillator has not a good stability ? What sould i check ?

I don't have expericence with oscillators , so sorry if my questions looks stupid .

Thansk in advance .

Nicola .

i have a problem with a simple 30.875Mhz (garage opener) crystal oscillator .

The problem is that the frequency it generates is not the expected one . On the attached schematics , if i measure the frequency using a frequency counter on "A" point i get 30.876Mhz which is correct , but on the other side of the 27pF capacitor at "B" only get 20.606Mhz .

My crystal is a 3rd overtone crystal , is it possible that it's oscillating at 2nd overtone frequency ? Why do i get a lower frequency on the capacitor ?

The output of my oscillator will be fed into a ASK modulator , so the capacitor is only needed to cut DC offset from next modulator stage . Why does it cut the frequency ?

Maybe the oscillator has not a good stability ? What sould i check ?

I don't have expericence with oscillators , so sorry if my questions looks stupid .

Thansk in advance .

Nicola .