Amplitude Modulation (AM) encodes information by varying the amplitude of a carrier wave. Frequency Modulation (FM) conveys information by changing the frequency of the carrier wave. FM is less susceptible to amplitude variations and noise, offering better signal quality than AM.
Key Takeaways
- AM (Amplitude Modulation) radio signals transmit information by varying the amplitude of the carrier wave, which is more susceptible to noise and interference, resulting in lower sound quality.
- FM (Frequency Modulation) radio signals convey information by altering the frequency of the carrier wave, providing better sound quality and resistance to interference, but with a more limited range compared to AM signals.
- The key difference between AM and FM lies in their modulation techniques, with AM adjusting the amplitude and FM altering frequency, which affects signal range, sound quality, and susceptibility to interference.
AM vs FM
AM radio transmits by varying the amplitude of the radio wave, while FM radio transmits by varying the frequency of the radio wave. FM provides better sound quality, while AM has a more extended range and is less prone to interference. AM stations have a stronger signal during the night, while FM stations have a stronger signal during the daytime.
Amplitude Modulation came into existence earlier than Frequency Modulation. The discovery of FM radio signals is an upgrade in signal clarity compared to AM radio signals.
Comparison Table
| Feature | AM Radio | FM Radio |
|---|---|---|
| Transmission method | Amplitude Modulation (AM) | Frequency Modulation (FM) |
| Sound quality | Lower | Higher |
| Range | Longer | Shorter |
| Susceptibility to interference | Higher | Lower |
| Bandwidth | Narrower | Wider |
| Frequency range | 535-1705 kHz | 88-108 MHz |
| Cost | Generally cheaper | Generally more expensive |
| Typical programming | Talk radio, sports, news | Music, public radio, specialty programs |
| Advantages: | Longer range, lower cost | Higher sound quality, less interference |
| Disadvantages: | Lower sound quality, more susceptible to interference | Shorter range, higher cost |
What is AM (Amplitude Modulation)?
Amplitude Modulation (AM) is a modulation technique used in analog communication systems to transmit information through variations in the amplitude of a carrier wave. It involves the combination of a low-frequency signal (audio or data) with a high-frequency carrier wave.
Key Components
- Carrier Wave: A high-frequency sinusoidal waveform that acts as the carrier of the information.
- Modulating Signal: The low-frequency signal containing the information to be transmitted. This signal modulates the amplitude of the carrier wave.
Modulation Process
- Mixing: The modulating signal and the carrier wave are combined using a mixer or modulator.
- Amplitude Variation: The amplitude of the carrier wave is varied in accordance with the instantaneous amplitude of the modulating signal.
Advantages
- Simple Implementation: AM is relatively straightforward to implement and requires less complex circuitry compared to other modulation techniques.
- Compatibility: AM receivers are widely available and can demodulate signals from various sources.
Disadvantages
- Susceptibility to Noise: AM signals are more prone to noise and interference, impacting signal quality.
- Inefficient Use of Bandwidth: AM utilizes a larger bandwidth compared to other modulation techniques, limiting the number of channels available.
Applications
- Broadcast Radio: AM is commonly used for long-wave and medium-wave radio broadcasting.
- Two-Way Radio Communication: AM is employed in various communication systems, including aviation and maritime communication.
What is FM (Frequency Modulation)?
Frequency Modulation (FM) is a modulation technique used in telecommunications to transmit information through variations in the frequency of a carrier wave. Unlike Amplitude Modulation (AM), which alters the amplitude of the carrier wave, FM encodes data by changing its frequency.
Mechanism:
- Carrier Wave:
- FM starts with a sinusoidal carrier wave, characterized by its frequency and amplitude.
- Information Encoding:
- The information to be transmitted is superimposed onto the carrier wave by varying its frequency in proportion to the variations in the input signal.
- Frequency Deviation:
- The degree to which the frequency of the carrier wave varies is known as frequency deviation. It is directly proportional to the amplitude of the input signal.
Advantages:
- Improved Signal Quality:
- FM is less susceptible to amplitude variations and noise compared to AM, resulting in better signal quality.
- Constant Amplitude:
- Since the amplitude of the carrier wave remains constant, the transmitted signal is less affected by amplitude-related distortions.
- Wide Frequency Bandwidth:
- FM signals occupy a wider frequency bandwidth than AM signals, allowing for the transmission of more information.
Applications:
- Broadcasting:
- FM is commonly used in radio broadcasting to achieve high-fidelity audio transmission.
- Two-Way Radio Communication:
- FM is widely employed in two-way radio communication systems, providing clear and reliable voice transmission.
- Frequency Modulated Continuous Wave (FMCW) Radar:
- In radar systems, FMCW radar utilizes FM techniques for accurate range and velocity measurements.
Main Differences Between AM and FM
- Modulation Method:
- AM (Amplitude Modulation): Encodes information by varying the amplitude of the carrier wave.
- FM (Frequency Modulation): Conveys information by changing the frequency of the carrier wave.
- Susceptibility to Noise:
- AM: More susceptible to amplitude variations and noise, which can affect signal quality.
- FM: Less susceptible to amplitude variations and noise, providing better signal quality.
- Signal Quality:
- AM: Prone to distortion and interference, especially in long-distance transmission.
- FM: Offers improved signal quality, making it suitable for high-fidelity audio transmission and communication.
- Bandwidth Usage:
- AM: Occupies a narrower frequency bandwidth compared to FM.
- FM: Requires a wider frequency bandwidth, allowing for the transmission of more information.
- Amplitude vs. Frequency Variation:
- AM: Information is encoded in the amplitude variations of the carrier wave.
- FM: Information is encoded in the frequency variations of the carrier wave.
- Applications:
- AM: Commonly used in medium-wave and short-wave radio broadcasting.
- FM: Widely used in high-quality audio broadcasting, two-way radio communication, and radar systems.
- Transmission Range:
- AM: Long-distance transmission is possible but with increased susceptibility to noise.
- FM: Better suited for medium-range communication with less susceptibility to noise.
- Receiver Complexity:
- AM: Simple receivers can demodulate and retrieve information.
- FM: Requires more complex receivers for demodulation due to the frequency variations.
- Constant Amplitude:
- AM: Amplitude of the carrier wave varies, impacting signal consistency.
- FM: Maintains a constant amplitude, contributing to signal stability.
- Frequency Deviation vs. Amplitude Modulation:
- AM: Information is encoded in the amplitude variations, directly related to the input signal’s amplitude.
- FM: Information is encoded in the frequency variations, directly related to the input signal’s frequency.
- https://www.osapublishing.org/abstract.cfm?uri=ol-31-15-2254
- https://arxiv.org/pdf/1808.08589
- https://pure.tue.nl/ws/files/2235569/Metis174587.pdf
Last Updated : 25 February, 2024
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Sandeep Bhandari holds a Bachelor of Engineering in Computers from Thapar University (2006). He has 20 years of experience in the technology field. He has a keen interest in various technical fields, including database systems, computer networks, and programming. You can read more about him on his bio page.
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While AM has its practical applications, the improved sound quality and resistance to interference make FM a preferable choice for most modern broadcasting needs.
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Although AM has a longer range, the superior sound quality of FM makes it a better choice for most broadcasting purposes.