Which antenna is preferred for amplitude modulation?

Sexl Physics 7, textbook

In the following sections, the transmission of large amounts of data (information) with the help of electromagnetic waves is discussed as an example. Experiment: Detection of Electromagnetic Waves 44.1 E 1 Use a transmitting and receiving system as shown schematically in 43.4. A lamp (1 V / 0.01 A) in the receiving antenna shows the currents induced in the antenna. First change the distance between the transmitter and receiver. What is happening? Now take a switched off cell phone and hold it next to the reception dipole with the lamp. Turn on the cell phone and watch the lamp. Describe and explain your observations. (More detailed description of the experiment at physikplus.oebv.at) Broadcasting (radio) For the transmission of acoustic signals one usually uses electromagnetic waves with frequencies in the range between 100 kHz and 100 MHz. A high-frequency generator generates these oscillations, which are fed to a transmitting antenna that is tuned to resonance. The electrons in the antenna are accelerated by the field, and high-frequency alternating currents are generated. These cause an electromagnetic field that spreads through space as an electromagnetic wave. In order to transmit information with a radio transmitter, it is necessary to influence the uniform, high-frequency electromagnetic wave which the transmitter emits in such a way that it becomes the carrier of the information, i. H. the carrier wave is modulated. You can either change the amplitude of the wave (amplitude modulation = AM) or the frequency of the transmitter (frequency modulation = FM) (see 44.1). The amplitude modulation is described below as an example. (For the mathematical consideration of information transmission by radio, see also physikplus.oebv.at) An oscillating circuit generates the high-frequency carrier wave of the transmitter. The low-frequency alternating voltage that is obtained at the microphone output modulates this wave, i. H. the amplitude of the high frequency oscillation is changed in the rhythm of the sound signals. This "amplitude-modulated oscillation" is fed to the transmitting antenna and emitted after it has been appropriately amplified. The incident electromagnetic wave causes charges to vibrate in the receiver's antenna, and the programs of many radio stations contribute to these vibrations. Only a closed resonant circuit coupled to the antenna selects the high-frequency oscillation of the desired transmitter from the mixture. For this purpose, the resonance frequency of the receiving oscillating circuit is set to the frequency of the desired transmitter with a controllable capacitor. The signal is then rectified, amplified and transmitted to a loudspeaker. Investigate, consider, research: Time information from radio-controlled clocks 44.1 S 1 Radio-controlled clocks receive their information via so-called time signal transmitters, which in turn are linked to atomic clocks. It uses radio waves with a long range. Gather information about time signal transmitters and explain why the antennas used are very large. Television and the Internet The most important media of our time are television and the Internet. We are often not aware of the extent to which they influence our thoughts and actions, and the full scope of dealing with these media has not yet been investigated. Television is the transmission of pictures with the help of electromagnetic waves. The images recorded with a television camera are saved on a CCD sensor (see also the section on semiconductors). I. E. optical signals are converted into electrical signals. These are amplified and emitted by a transmitter in the form of electromagnetic waves. The receiving antenna converts these signals back into electrical signals, the conversion back into optical signals (images) takes place in the television set. 44.2 Listening to the radio around 1930 was a social event. A whole family listens with headphones to see what can be coaxed from the detector radio. 44.3 In cell phones, the pixel density plays a major role in the quality of the displays. The images are sharply focused and the display can also be viewed from the side. Time t Sine carrier audio frequency signal Amplitude modulation (AM) Frequency modulation (FM) Time t Time t Time t 44.1 Amplitude or frequency modulation of a high-frequency carrier wave with a low-frequency signal. 44 ELECTROMAGNETIC SHAFTS For testing purposes only - property of the publisher öbv

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