Lab 05: RF Amplifier

One of the engineering challenges in creating an AM radio is dealing with the very low voltage these antennas create, usually on the order of 20 to 40mV. This input signal must be amplified so that it can be properly processed in order to produce a quality sound on the output. I began this lab by first creating a common source amplifier (CS) and measuring the Q-point and gain for the amplifier, both with and without the RFC inductor. My results are included in the chart below:

I then added a common emitter (CE) amplifier in order to create a two stage amplifier. The results of my measurements of the gain of this amplifier for various load resistances is included below.

Shown below is the logarithmic graph comparing the voltage gain of the amplifier as load resistance increases:

After completing the testing of the two stage amplifier, I connected the two stage RF amplifier, AM detector, and the LM386 amplifier together to form my AM radio circuit. To test its performance I connected the speaker to the output and used the function generator to produce a 22 mV 1kHz AM signal, simulating a voltage similar to what would be produced by an antenna. The resulting sound output was loud, clear, and distortion free. Finally, I replaced the function generator with an antenna provided by the lab TA, and was able to recieve AM radio signals from a nearby broadcasting station. The sound was not perfectly clear, but the announcer's voice was easy to hear. Overall, I was impressed with the performance of my radio, but I have plans to reduce some of the fuzziness I heard by eliminating some long wires that may be negatively impacting the performance of the AM radio.