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I would like to make a module for OOK transmission using a generic DIP8 Crystal Oscillator, and this is what I currently have.

OOK

How is the output impedance of a Crystal Oscillator determined?

George
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    That would depend on which specific module it is, so you can read the datasheet to figure out what kind of output stage it has and what kind of loads it is meant to drive. – Justme Apr 30 '21 at 11:44
  • This might help: Crystal Oscillator Output Impedance and Output Voltage: ham.se: https://ham.stackexchange.com/questions/17612/crystal-oscillator-output-impedance-and-output-voltage – tlfong01 Apr 30 '21 at 12:15

2 Answers2

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Assuming it's a digital output, not sine wave output, it's typically not specified in the data because it's not terribly useful and it isn't constant- it will be different for high and low states, for example. It will also vary with supply voltage etc. It will also be lower for light loads than for heavy loads.

Probably somewhere in the 100 ohm range, give or take 75 ohms. With a light load a CMOS buffer is more like 15 ohms, but working into a low impedance it's more like a constant current source.

Spehro Pefhany
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There's an ASIC in it, and its output looks like a logic gate, but impedance and drive strength depends on what's in the box, which will depend on manufacturer, frequency range, etc. Expect 10-30 ohms.

If you intend to drive a 50 ohm coax with it, I'd recommend adding a source termination resistor on the output, somewhere around 30 ohms. Plug the other end into a scope with the input in 50 ohms mode (or use a terminator), and spend a little time tuning the resistor value to get the cleanest edges without ringing.

bobflux
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