Lab 06: Square Loop Antennas

The goal of this lab was to develop and test an antenna for use in the AM radio. The antenna used a square loop design, constructed as many loops of 'magnet wire', copper wire coated in a thin insulator. These loops were wrapped around a pizza box for a frame in order to hold the loops in shape. In Auburn, the primary AM radio stations are found at 1230 kHz, 1400 kHz, and 1520 kHz. in order to recieve these stations, I had to determine the proper impedance for the antenna to 'tune' to a particular station. This tuning is accomplished by using a variable 'trimming capacitor' in parallel with the antenna. Adjusting the capacitance of the trimming capacitor adjusts the resonance frequency of the antenna, therefore adjusting the frequency recieved by the radio.

In the lab, my partner and I assembled the antenna. After the box was wrapped with loops of magnet wire, we soldered normal insulating wire onto the ends of the magnet wire so that we could attach the antenna to the input of our AM radio. Using a spectrum analyzer, we determined that the antenna we made was receiving a peak at around -20 dB at its resonance frequency, an average figure. When we plugged it into the input of the AM radio circuit, we were able to hear an AM radio station with discernible voices, but it wasn't a totally clear sound.

We then placed a trimming capacitor in parallel with the antenna and attempted to 'tune' the AM radio by adjusting the capacitance which alters the resonance frequency of the antenna. Using the trimming capacitor, we were able to receive three seperate stations with decent clarity.