M1

• Ways of transmitting radio signals are Amplitude Modulation (AM) and Frequency Modulation (FM). In the form of electromagnetic waves, both AM and FM transmit information. Amplitude Modulation works by varying or modifying the signal or carrier amplitude transmitted according to the information sent while maintaining a constant frequency. The modulation of frequency differs in the way that the information (sound) is encoded. It could be done by varying the wave frequency and keeping the amplitude constant.
• A radio show or program starts with the production of audio from people who speak. The sounds will then be captured, and the microphone will turn them into an electrical signal. It is then transmitted from the studio immediately or stored as a recording to be used later, but here is where the AM/FM thing happens.
• It should be combined in the radio wave called carrier wave to broadcast an electrical signal. This mechanism is called modulation. Modulation refers to converting data by adding information to an electronic or optical carrier signal into radio waves. One with a steady waveform is a carrier signal - constant height, or amplitude, and frequency.
• There are two ways for the carrier wave to be modulated (or changed):

  
  

  1.  By changing the amplitude or height of the carrier wave (Amplitude Modulation).

  2. By changing the frequency or how fast the carrier wave travels (Frequency Modulation).
• The signal is then broadcast as electromagnetic waves from the radio station’s antenna. The receiver of the personal radio or home radio then picks up the waves, amplifies, and converts them back into sound through the speaker. If the signal is not attached, the sound will not be produced because the carrier waves are not modulated.
• Despite that radio waves continuously coming from many stations surrounding us, the radio receiver does not receive them simultaneously. It is because the stations broadcast at different specific frequencies. The radio has to be tuned in to a precise frequency to find the right signal. The numbers on the radio dial represent frequencies used by the local radio stations. If the FM dial is set at

  107.5 (WISH 107.5), the radio signal is broadcasted at 107,500,000 MegaHertz (MHz), or 107,500,000 cycles per second.
• The quality of sound produced, performance, and broadcast range of AM and FM can be associated with the way radio signals are encoded. The quality of sound varies on its location and environment. If there are physical barriers like buildings or in closed area, the quality might be affected. It explains why FM stations sound better than AM stations, but AM stations can be heard further.
• AM radio varies the amplitude of the broadcast signal, so the signal’s power is also changed since amplitude represents the signal’s strength. Some receivers cannot pick up low amplitude signals at all. FM radio always remains at constant amplitude, so signal strength does not change.

   
• FM uses a higher frequency range and bandwidth than AM. AM radio operates from 535 kHz (kiloHertz) to 1705 kHz. When turning the dial on the radio, the number changes by 10 kHz each time. It means that each station has 10 kHz of bandwidth on which to broadcast. On the other hand, FM radio operates between 88 MHz and 108 MHz and increments every 200 kHz.
• FM station has an allocated 150 kHz of bandwidth, which is 15 times that of an AM station. It means that an FM station can transmit 15 times as much information as an AM station. It explains why music sounds so much better on FM. Since music has more electrical information than a monophonic voice audio signal, FM typically broadcasts music, and AM generally sticks to news and talk show programs.
• In alternating current, the zero-crossing is the instantaneous point at which there is no voltage present. In a sine wave or other simple waveform, this normally occurs twice during each cycle. It is a device for detecting the point where the voltage crosses zero in either direction.
• The zero-crossing is important for systems which send digital data over AC circuits, such as modems, X10 home automation control systems, and Digital Command Control type systems for Lionel and other AC model trains.

   Counting zero-crossings is also a method used in speech processing to estimate the fundamental frequency of speech.
• AM stands for amplitude Amplitude
• FM stands for frequency modulation
• AM method of audio transmission was  first successfully carried out in the mid-1870s.
• FM radio was developed in the United States in the 1930s, mainly by Edwin Armstrong.
• In AM, a radio wave is called the “carrier” or “carrier wave. “It is modulated in amplitude by the signal that is to be transmitted. The frequency and phase remain the same
• In FM, a radio wave is called the “carrier” or “carrier wave.” It is modulated in frequency by the signal that is to be transmitted. The amplitude and phase remain the same
• In FM, a radio wave is called the “carrier” or “carrier wave.” It is modulated in frequency by the signal that is to be transmitted. The amplitude and phase remain the same.
• AM has a poorer sound quality than FM, but it is cheaper and can transmit over long distances. It has a lower bandwidth, so it has more stations available in any frequency range.
• FM is less prone to interference     than     AM. However, FM signals are impacted by physical barriers. FM has better sound quality due to higher bandwidth.
• AM radio ranges from 535 to 1705 KHz (OR) Up to 1200 bits per second.
• FM radio ranges in a higher spectrum from    88          to           108

  MHz. (OR) 1200 to 2400 bits per second.
• Twice the highest modulating frequency. In AM radio broadcasting, the modulating signal has a bandwidth of 15kHz hence, the bandwidth of an amplitude-modulated signal is 30kHz.
• Equidistant


  AM
• Not Equidistant 


  FM
• Twice the sum of the modulating signal frequency and the frequency deviation. If the frequency deviation is 75kHz and the modulating signal frequency is 15kHz, the bandwidth  required     is 180kHz.
• Transmitter and receiver are simple, but synchronization is needed.

  AM
• Transmitter and receiver are more complex as the variation of modulating signal. It has to be converted and detected from the corresponding variation in frequencies. (i.e. the voltage to frequency and frequency              to           voltage conversion has to be done).

  FM
• AM is more susceptible to noise because noise affects amplitude, where information is “stored” in an AM signal.
• FM is less susceptible to noise because the information in an FM signal is transmitted through           varying             the frequency, and not the amplitude.