Can someone explain to me how this crystal oscillator circuit works? I built it and it works but i just don't know how.
http://cxem.net/rmodem/images/rmodem17-14.png

 

OK, look at the circuit.

The amplifier is the thing. You have a common base element where C2 provides positive feedback. It is a form of Colpitts oscillator.

Then there is the crystal. Crystals have two modes, one right next to the other. One of them is a simple bandpass, but the other phase changes the signal 180°. The latter provides positive feedback for the resonant frequency when the same transistor circuit is viewed a common emitter configuration.

I cut my teeth on these old CB transmitter circuits. You left off the audio modulation section. A real blast from the past that.

 

So by CB do you mean citizen band? sorry I'm a noob. I was thinking about leaving off the modulation portion and just using the 27.145 MHZ carrier. I wanted to use the carrier itself to set off a buzzer on the receiver end.

 

also, can you please explain how this works?

http://www.pyroelectro.com/projects/pyro_rf_receiver_27mhz/img/schematic_2.png

 

I wanted to use the carrier itself to set off a buzzer on the receiver end.

Any signal that appears on that frequency will set off your buzzer. This may be a low risk and not a problem, but I wouldn't want to be wearing a shock collar that would go off if it sees that frequency.

 

This circuit...

Is a basic transistor common emitter amplifier.

The common-emitter amplifier

It works, but has a multitude of problems, and is not usually used for analog design because of it. Basically it is one of the first amplifiers taught in school.

It is an inverting amplifier, medium impedance in, medium impedance out. By tying the base resistor collector to the collector output some negative DC feedback is created, which helps stabilize DC drift.