In this week's lab activity, I participated in the most astounding engineering project of my life: building a square loop antenna for a complete, functioning AM radio. Before studying the lab activity, I had never understood exactly how antennas captured radio signals (still to this day I do not have the greatest of clarity although I understand a great deal more than before); nevertheless, I undertook the task of creating one using a pizza box (unused box). After a brief introduction to antenna theory in lab lecture, I worked through the following exercises in lab to create my own antenna for my AM radio.
First, I was introduced to the physical design parameters of the square loop antenna: copper wire wrapped around a pizza box. This physical parameters, such as the length of the sides of the box A; the width of the wrapped wire on one side of the box B; and the number of loops (how many times the copper wire is wrapped around the box) N (shown in Figure 1), are of upmost importance because they severely affect the electrical properties of the antenna, giving it an inherent inductance and capacitance.
To determine the electrical properties required for the antenna to function properly, I calculated the inductance (at a capacitance of 60 pF) required to pick up the 1400 kHz station as roughly 215 micro-Henries. Next, using a MATLAB script which I had written to solve Joe Carr's Formula (Equation 1), I used the physical dimensions of my pizza box (parameters A and B) and the inductance calculated in the previous step to solve for N, which I calculated to be 17. Then, using these numbers, I calculated the inherent capacitance of the antenna at the 1230 kHz (max C) and 1520 kHz stations (min C), which I calculated to be 78 pico-Farads and 51 pico-Farads respectively. Using these numbers, I wrapped the copper wire around the pizza box, taped the wire down, and sanded down the coating on the ends of the wire, creating my square loop antenna (Figure 2).
Finally, after constructing the final part of the AM radio, I was able to put it all together and create a fully functional AM radio. Upon plugging up the battery, I received great amusement and satisfaction when I heard the glorious sounds of ESPN Radio blasting the announcers' calls from the World Series (Braves vs Astros 2021). Figure 3 shows the square loop antenna connected to the complete AM radio circuit.
After finally combining all the individual parts of the radio from previous weeks into one functioning device, I have received a sense of satisfaction in my creation and awe at the engineering feat of such a device. This is my most spectacular engineering achievement so far, and I am grateful for the opportunity to learn about the AM radio and build one.
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