Lab 4 - AM Detector
Figure 1 - Example of Extracted Audio Signal from CFP Detector
The first AM detector we tested was a simple diode detector. Using the function generator, we sent an AM signal to the simple detector circuit with a carrier frequency of 200kHz and 50% modulation.
As I ramped up the power of the function generator, I could not make the circuit turn on. As R1 was changed to 10k and 100k ohms, I had the same result of no output.
Figure 3 - Weak Signal Extracted from Biased Detector Circuit
The final AM detector circuit I constructed was the Complementary Feedback Pair (CFP) detector. Feeding the same AM signal through this detector, but with varying amplitudes, the CFP detector was able to extract a clear audio signal even from weak AM signals.
With the results I've seen from all of the detector circuits, I decided to choose the CFP detector. This detector extracted a clear audio signal, even from weak AM signals.
In this lab, I learned about the function of an AM detector, as well as different types of AM detectors. The purpose of the AM detector is to extract the audio signal from the AM signal, and then we would pass the audio signal through our amplifier.
As with previous labs, our experiments were simulated beforehand in the prelab, and then tested during the actual lab meeting. As described in detail below, we tested a few types of AM detectors and took note of their performance.
Ultimately, we ended up choosing an AM detector that would work well with a weak signal and not cause much distortion.
Figure 2 - No Signal Extracted from Simple Diode Detector Circuit
Next, I constructed the biased detector circuit by adding a power source to the circuit. Feeding the same AM signal to the detector circuit, I was able to extract a signal that had a bit of distortion.
While the biased detector circuit worked, it is less than ideal since it requires a strong signal input and causes some distortion.
Figure 4 - Clear Signal Extracted by CFP Detector
Figure 5 - Output of CFP Detector and Amplifier
In the final experiment for this lab, I added the CFP detector circuit to my amplifier circuit. With the circuit properly assembled, I fed a 1230kHz AM signal to the circuit with 50% modulation.
When I connected the speaker to the output of the circuit, it gave me a decent sound quality that was greatly amplified from the original source. The gain of the circuit was approximately 20 V/V.
In this lab, I learned how a AM detector circuit can extract and clean up an audio signal before passing it on to the amplifier. This should have a significant impact on the quality of the radio that will be built in lab.