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Old 09-26-2010, 08:58 PM
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Aaron Aaron is offline
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Join Date: Feb 2007
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colpitts oscillator

Quote:
Originally Posted by Duncan View Post
I’m assuming that a basic oscillator circuit something perhaps after this style COLPITTS 1 To 20 MHz Crystal Oscillator is about the ticket,

I also believe it’s a bad Idea to try and “load” an Xtal at Its fundamental frequency. It’s basically Impedance matching that I see as being a problem if you deviate from Mikes 20Mhz plan. You may have to “dampen” the oscillations when you first set up your oscillator after that you really don’t want the oscillator “to see” any variation (load) in its operating conditions.
Nice! Last night I went through some crystal oscillator schematics and
THAT is the EXACT one I have sitting in another tab right now. Didn't
want to post about it until I had some feedback on my post. I'll take the
synchronicity as a good sign - and there are countless choices



Does anyone else see any reason why this simple circuit would not work
for the purposes in Mike's diagram?

Duncan, I see what you're saying about directly "loading" the source
crystal/frequency.

But still, my question is - does it even matter?

If the frequency changes by directly "loading" it, the secondary
frequency through the double and tripler will simply still be a double
then tripled frequency of the original and the difference of and sum
of those two frequencies will always still be an exact difference and
exact sum of those two frequencies. So, no matter how the 120MHz
crystal deviates, there is still 4 wave mixing happening.

Does it shorten the life of the crystal? If not, then damaging the crystal
this way isn't an issue.

The only issue I see if there is deviation in the frequency of a single
120MHz crystal is if there is an advantage to having a dead on source
frequency in the water where the antennas are. If breaking the 2x4
piece of wood by jiggling it at both ends with two frequencies will happen
just as effective with a crystal that deviates in frequency up and down
a bit, then a single 120MHz crystal will eliminate a double and tripler
on the input path to the amplifier and other double/tripler circuit.

I understand replicating systems means to do it EXACTLY. However,
if 120MHz crystal availability that long ago has anything to do with it,
then we can take out two blocks from the diagram. It really is only a
question that Mike can answer because he knows the reason he went
with a 20MHz one to start with. Hopefully, he will see this when he gets
back.
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Sincerely,
Aaron Murakami

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