In general, the radio wave is an electrostatic radiation of energy produced by an oscillator circuit. In a magnetic field created by an alternating current, the field expands, collapses, and changes polarity in step with the frequency.Īn oscillator can produce high-frequency alternating currents that produce a radio wave when connected to an antenna. In the study of electromagnetism, we learned that a conductor carrying an electric current is surrounded by a magnetic field. First, we will discuss the power source for this radio.Ī radio wave is an electromagnetic radiation produced from current alternating through an antenna.Ī transmitting antenna is surrounded by electromagnetic radiation. Take special note of the fact that there is no battery or other conventional power supply for this radio. Today’s radios and televisions operate from the same principles just described, but they are a significant refinement of the crystal set. The performance of this radio, however, is extremely poor by today’s standards. When constructed properly in the lab, you can actually receive and hear a few stations. The radio described is known as a crystal radio receiver. The description above may sound simple, and that is because this is the simple operation of a radio receiver. The detector diode and filter capacitor are necessary to change the broadcast frequency and audio signal to a reproducible sound at the headphones. The filter capacitor smoothers the high frequency of the audio portion of the radio signal. The detector rectifies the radio signal to a pulsing dc signal. The other frequencies (1040 station 3, and 1460 station 2) will not produce a large voltage drop across the tank circuit. Receiving a frequency of 920 kHz will cause the greatest voltage drop across the tank circuit. As we know that an inductor and capacitor connected in parallel will have a resonant frequency.īy using a variable capacitor, you are able to vary the tank circuit resonant frequency until it matches the frequency of the desired station.įor example, if we wish to tune in station 1, the capacitor is varied until the resonant frequency of the tank circuit is equal to 920 kHz. The tank circuit consists of an inductor and a variable capacitor connected in parallel. A simple crystal radio can receive AM radio signals and convert them to sound. The antenna circuit is coupled to the tank circuit by mutual induction.įigure 1. The antenna converts the radio signals to alternating current, which is conducted up and down the antenna to the ground. The radio waves of all three stations come in contact with the radio receiver antenna. Station 1 is broadcasting at AM 920, station 2 at AM 1460, and station 3 at AM 1040. Each station is broadcasting a radio signal consisting of a carrier wave and an audio signal. In Figure 1, there are three radio stations each broadcasting at a different wavelength.
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