crystal oscillator circuits

Posted on Feb 5, 2014

The circuit below is a standard oscillator of the Colpitts variety. Similar circuits have been used in many ham radio homebrew transmitters. This particular circuit should function well at frequencies from 1500 kHz to 8000 kHz. For use on lower frequencies, the values of C1 and C2 might need to be increased. If you`ve never built a circuit from a

crystal oscillator circuits
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schematic before, this might be a good one to start with. The diagram below shows how you can arrange the parts on a prototyping board such as Radio Shack catalog number 276-175. (A prototyping board, also called a solderless breadboard, contains groups of holes that are electrically connected. Each hole has a little spring/clamp thingy in it that grabs ahold of the component leads. This is a great way to experiment with circuit designs and learn about the building process. ) Attach a 10-inch (25 cm) piece of bare wire to the output, then sit a radio next to the circuit and tune to the crystal frequency. Apply power. If everything is connected correctly and all the components are in working order, you will hear the carrier (or the silence caused by it) on your receiver. Now all you need to do is add a buffer amp, a modulation stage, a final RF amp, a harmonic suppression and output matching section, and you`ve got an AM transmitter. :-) Below is another version of the circuit with a couple of enhancements. The variable capacitor between the crystal and ground allows you to adjust the frequency slightly. (More capacitance equals lower frequency. ) Q2 serves as a buffer amplifier which stabilizes the circuit and boosts the output power. This circuit was developed independently by another MWA member and uses very different values for R1, C1 and C2 compared to the first circuit on this page; don`t let those differences scare...

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