4. Lab 4 - Voltage Controlled Oscillator

posted Mar 2, 2010, 7:11 PM by Bill Bai
The voltage controlled oscillator is another important piece of the FM radio tuner.  The VCO is the Local Oscillator.  Basically, the VCO selects what frequency the radio is tuned in to.

The nuts and bolts are fairly complex, but what it boils down to is: the output frequency changes as you change the input voltage.  Hence the very descriptive name Voltage Controlled Oscillator.

So the VCO output is connected to one of the mixer inputs.  This creates the harmonics and cross products of the Radio Frequency signal and Local Oscillator Signal at the Mixer output.  As you may recall in the last post, Mixer's create a lot of harmonics and cross products.  The nice thing about them is that each cross product contains all of the information originally embedded in the carrier signal.  The next stage of the radio will be using one of these lower frequency cross products to extract the information.

Lab Report attached,  Haven't gotten it back yet, don't know what I got on it.
Bill Bai,
Mar 2, 2010, 7:27 PM