Using transistor for the amplifier of the oscillator.
It' s clear that if we want to create high frequency sinusoids we have to works with a transistor instead of an OP amp.
The structure of the oscillator that we want to study is made of an amplifier made with a transistor and with an amplify of 1, a resistance of input high and a low impedance at the output, in other words this is a voltage buffer (esp: seguidor de tension). The band pass filter have an amplification higher that 1 in the peak of resoncance.
First of all we study that circuit without the connection input-output, so we find the condition of oscillation and the frequency of the peak (that depend also on the value of a variable capacitor).
In a second step we study the design for the voltage buffer, hence we found the equation for the polaritation of the transistor (obviously we used the little signal model for the transistor).
Finally we dimensioned all the value of the rsistance inductance and capacitors to obtain an oscillator fot 27 Mhz.
After the theory part of the lecture we went to the laboratory to build the circuit and to test it. We simulate the load of the antenna with a resistence and we used an autotrasformer that Jose Maria given us. We have to measure the power that is trasmitted to the resistance (the "antenna") we have to observed that we don' t obtain a perfect sin wave and therefore we understand that the power that we measured is not only of the component in the 27Mhz.
The quality of an oscillator stay in how much are attenuated the armonics of the principal frequency f0.
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