Written Report
Team Procrastination

Radio-Lab Report

Design Description

We knew from the start that the way to approach the project was to focus on only two goals: better reception of radio signals and the amplification of the output. The crystal radio set from Radio Shack had already proven that we could tune across the entire AM broadcast band, therefore to alter the LC portion of the radio would probably do more harm than good. With this in mind we started the most tedious part of our project, the R&D.
Our previous work with op-amps provided a good starting point. The gain achieved by a standard op-amp is so great that we believed it would convert a relatively small voltage from the antenna into a larger voltage to put into the speaker. The final homework assignment contained a very useful schematic of an op-amp radio circuit. The most important hint that it gave was the portion of the circuit that filtered out noise ( In the schematic it is the RC loop directly after the diode.) With a little fine tuning that example would make an excellent little radio, however we wanted something even more powerful. What followed was countless web searches for many hours with the intent of finding a way to use an op-amp (or more than one) to get better amplification. Something that found its way to us was a schematic entitled “Simple Op-Amp Radio”. We had tinkered with using two Op-Amps in series in the hopes of getting outrageous gains, what we didn’t realize is that there is an Op-Amp readily available at Radio Shack that essentially does just that, it’s a combination of two Op-Amps (Cleverly disguised as one Op-Amp). The purpose of the first Op-Amp is to buffer the signal, while the second actually does the amplification. Also, the circuit uses a transistor to amplify the signal even more. (Encarta encyclopedia provides a fair description of how the transistor works) The circuit depicted, however, varied from the LC portion which we were determined not to change. It did show us how to use the 1458 Op-Amp, though, and even provided us with initial values for resistors. After testing and experimenting, those values were the best. After fusing this amplification with our original crystal radio (we actually went to Radio Shack and bought a set to stay consistent) we had taken care of the amplification part of our design goal.
It seems that everyone who has ever built an AM radio has a different opinion about what to use for an antenna. Some of them are quite fascinating, but after careful consideration we decided to use the AM antenna from a home stereo system coupled with the antenna provided in the Radio Shack kit. (The longer the better, hopfully.) Unfortunately we were not able to test the antenna (through ignorance probably) we were only able to test the circuit by replacing the antenna with a AM signal from the function generator.
We set up the radio in the lab and connected it to an AM signal to see how well it responded. It was impressive. At 2mv pp we were able to hear frequencies of around 50kHz, well below the broadcast range. We tried multiple signal strengths and frequencies, and are confidant that our radio will perform well. (assuming the antenna works)

“In a surprising upset Team Procrastination dominated the competition to prove that, although they are slacker ski bums, they have what it takes to go all the way.”