The Physics of an AM Radio Receiver :: Radio Technology Electronics Essays

The Physics of an AM Radio Receiver The AM Radio has been around for a long time. When the AM radio was first invented, it was not meant to be used to broadcast music. That is why today most music radio stations are on the FM band. Instead, the AM band was used to carry voice frequencies, thus, all the AM talk radio stations. Due to new technology, music is broadcast over the AM band but does not have the same sound quality as the FM band. According to the FCC regulations at www.fcc.gov, the AM broadcasters are only allowed 5 KHz each side of their carrier frequency for their side bands. These side bands will be explained in more detail later on. In order to understand an AM receiver, one must understand each stage and what it does. An AM receiver can be broken down into six stages. These stages will be explained one at a time. The first stage is the RF amplifier. The AM antenna runs into the RF amp where the desired frequency is selected. As stated by Grob (1997), the typical band for AM is 535 Hz to 1605 KHz. For the duration of the paper, we will assume that we are trying to receive a station that is located on 1290 KHz signal. The antenna used must be able to pick up all the stations on the AM dial. Knowing this, we need to select the one we want to hear. In this case, we want 1290 KHz or The Country KOWW. When the dial on the radio is turned to select 1290 KHz, it does two things. There are two variable capacitors The Physics of an AM Radio Receiver being adjusted. I will begin by discussing the first capacitor. This capacitor is connected in parallel with an inductor. While the capacitance changes as the dial is turned, the resonant frequency of the LC circuit also changes. This process is called inductor and capacitor in parallel. When the capacitor is in just the right spot, the resonant frequency will be 1290 KHz. This LC circuit is designed so that only the resonant frequency is passed. The 1290 KHz will now be passed on to the next stage and all other frequencies will be filtered out. The RF amp must also have good sensitivity, which according to Scott Rasmussen (2003), is the ability to amplify a very weak signal.