Week 5 Activities

It was the last lab day for us to conduct the project, we also had the extra lab time in this week Wednesday. Good news for us is that the AM transmitter was completed, which can be normally working. The AM radio can receive the signal from the transmitter and we can hear the sound. Although there is much noise, but in terms of the AM simplified transmitter, the quality of the sound is appropriate.

For the last week, there were some problems about the transmitter, and this week, we found the solutions. For the circuit design, there was an error. We immediately changed the design and the circuit for transmitter, as a consequence, the circuit was working.

Therefore, the new and final design for the transmitter is shown below. There are two changes for the design. Firstly, R8 is removed, because R8 was in series with R6, which was not sensible. An other change is that, C6 was originally connected to R8 directly, when R8 is removed, we changed C6 connected to the base of Q2. Moreover, at the beginning, we chose to use a MP3 as the input signal; however, the sound can be heard more clearly than by using MP3. The real circuit is finally determined, as indicated below in the figure and video.

The result for testing in the video was the best result we have ever got throughout the whole project.

After several times test, the noise became larger which almost cover the sound and the frequency was decreased. We checked the circuit for a few times and ensure that the circuit is correct. Then we replace the components used in the circuit with new ones and test again. It turns out that the noise caused by the loss of the components. We also measured the value of the inductor again and find that the value of the inductor change from 540uH to 600uH. This is the reason why the frequency decreased to 650kHz.

After the transmitter completed, we also tried to make the receiver. Nonetheless, we still could only hear the noise but no AM programme received. The noise indicates the circuit is passing, but no sound heard also demonstrates the circuit has a lot of problems. Moreover, because it is a very simple receiver, the sensitivity and the stability cannot be the same as the produce of an AM radio.

The design for receiver was changed for removing the C4,C5,R2,C11,C12, we connect both PIN 6s to the battery, and the circuit is also constructed, but the circuit does not work. The circuit is shown below.

The circuit for receiver looks more complicated than the one for transmitter, however, in fact, for the practice, the receiver ought to be easier to work and be more stable. Therefore, for the purpose of completing the transmitter and receiver, we only achieve the the goal of transmitter, which is the more difficult one.

Although, there is no enough time of the project for us to complete the receiver, in terms of the further research, we should like to learn more about the receiver.