Simple AM transmitter

[mstechca]

No! 0/X = 1/infinity. Way too much attenuation.

Ok, I think what you are trying to say is that your equation is the equation for gain. Isn't attenuation opposite of gain? after all, an attenuated signal is a loss of signal or very poor signal.

 

[audioguru]

An signal that is attenuated on purpose is one whose amplitude is reduced to the amount that is required.
Simply put, to make an oscillator without too much distortion, you need just enough positive feedback so that the overall gain is a little more than 1. Since the oscillator's amplifier has a certain amount of gain, you must attenuate its output by about the same amount so that the overall gain is a little more than 1. If you attenuate its output too much so that when it amplifies it then its output is less each time around, then it won't oscillate. If you don't attenuate the feedback enough, then the signal is amplified more each time around and its output will be square waves with lots of harmonics.

 

[joeypc]

Well, I have some questions about oscillators too. In this circuit, how'bout the connecting ground base capacitor ? When I remove this capacitor, it won't oscillate too, but in some designs I've found on the web, this capacitor doesn't connect ground (mass) but connect Vcc ? So what are the differences between these designs ? Could anyone here answer this qestion ?
Thank you for your answers !

 

[audioguru]

The supply is supposed to have a bypass capacitor to ground so that the supply isn't bouncing up and down at the RF frequency. The common-base transistor oscillator is supposed to have its base bypassed to ground with a bypass capacitor. Then the common-base transistor oscillator can have its base bypassed to the positive supply or to ground.