How Do AM and FM Work and Which Is Better for Radio?
The Difference Between AM and FM is a frequently tested topic in exams because understanding their properties helps students solve questions on communication systems, signal transmission, and radio technology. Comparing these two modulation methods clarifies concepts crucial for both board and entrance exams like JEE and NEET.
Definition of AM
AM, or Amplitude Modulation, is a technique where the amplitude of a high-frequency carrier wave is varied in proportion to the instantaneous amplitude of the modulating signal or information source. Its frequency and phase remain fixed.
AM waves have a longer wavelength, allowing them to travel greater distances. This property is widely used for radio broadcasts and aviation communications. Related topics include the Difference Between Frequency Modulation And Amplitude Modulation.
Definition of FM
FM, or Frequency Modulation, is a process in which the frequency of the carrier wave changes according to the amplitude of the modulating signal, while the amplitude of the carrier stays constant throughout.
FM is preferred for high-fidelity transmissions such as music and entertainment because it is less susceptible to noise. It requires larger bandwidth compared to AM and is majorly used in urban radio stations. For comparison of analog techniques, see Difference Between Analog And Digital.
Difference Table
| AM (Amplitude Modulation) | FM (Frequency Modulation) |
|---|---|
| Amplitude of carrier wave is varied | Frequency of carrier wave is varied |
| Carrier frequency remains constant | Carrier amplitude remains constant |
| Requires smaller bandwidth (about 10 kHz) | Requires larger bandwidth (about 200 kHz) |
| More affected by noise and interference | Less affected by noise |
| Lower sound quality | Higher sound quality |
| Frequency range: 535–1705 kHz | Frequency range: 88–108 MHz |
| Can travel longer distances | Covers shorter distances |
| Signals can reflect off the ionosphere | Signals usually travel in straight lines |
| Simple transmitter and receiver design | More complex transmitter and receiver |
| Used in aviation and marine communication | Used for high-quality music transmission |
| Power consumption increases with signal strength | Power does not vary with signal strength |
| Less expensive equipment | More expensive equipment |
| Good for rural and remote transmissions | Preferred in urban and dense areas |
| Used in long-distance terrestrial broadcasting | Used in FM radio, two-way radios |
| Susceptible to amplitude-based interference | Resistant to most amplitude-based interference |
| Transmits mono signals | Can transmit stereo signals |
| Demodulation is simpler | Demodulation requires higher technology |
| Cheaper broadcasting infrastructure | More costly broadcasting setup |
| Audio quality can be poor during interference | Audio remains clear during minor interference |
| AM waves have lower frequency | FM waves have higher frequency |
Key Differences
- AM varies amplitude, FM varies frequency
- AM uses small bandwidth, FM uses large bandwidth
- FM is less susceptible to noise than AM
- AM is useful for long distance communication
- FM delivers higher audio fidelity
- FM receivers are more complex than AM
Examples
An AM radio station broadcasting news over 800 kHz modulates the amplitude according to the speech signal. In contrast, an FM station transmitting music at 101.4 MHz varies the frequency with the audio signal.
For further clarity on signal types, study the Difference Between Analog And Digital article.
Applications
- AM: Aviation communication systems
- FM: High-fidelity music radio stations
- AM: Marine navigation and news broadcasts
- FM: City-based two-way radio systems
- AM: Emergency long-range communication
- FM: Police and security radio communications
One-Line Summary
In simple words, AM changes the carrier amplitude to encode information, whereas FM changes the carrier frequency to achieve the same purpose.
FAQs on What Is the Difference Between AM and FM?
1. What is the main difference between AM and FM?
The main difference between AM (Amplitude Modulation) and FM (Frequency Modulation) lies in how the information is encoded onto a carrier wave:
- AM: The amplitude (height) of the carrier wave varies to represent the audio or data signal.
- FM: The frequency (number of cycles per second) of the carrier wave changes according to the information signal.
2. Which is better: AM or FM?
FM is generally considered better than AM for most audio broadcasting because:
- FM signals offer higher sound quality & reduced noise interference.
- AM can transmit over longer distances but is more affected by static and external disturbances.
3. Why is FM preferred over AM?
FM is preferred over AM because it provides:
- Better sound quality due to greater resistance to noise and interference.
- Consistent audio clarity regardless of signal strength fluctuations.
- Wider bandwidth that supports high-fidelity music and audio transmission.
4. What is AM modulation?
AM modulation is a process where the amplitude of a high-frequency carrier wave is varied in proportion to the audio or information signal. Key features include:
- Simple circuitry and transmission process.
- Vulnerability to noise and interference.
- Shift in amplitude represents the original message.
5. What is FM modulation?
FM modulation is a type of modulation where the frequency of the carrier wave varies based on the information signal, while the amplitude stays constant. Important points:
- Better noise immunity compared to AM.
- Wider bandwidth requirement.
- Used for music radio, TV sound, and two-way radio systems.
6. What are the advantages of FM over AM?
FM (Frequency Modulation) offers several advantages when compared to AM (Amplitude Modulation):
- Superior audio quality with less distortion and noise.
- Greater resistance to static and electrical interference.
- Supports stereo sound and high-fidelity music broadcasting.
- Stable reception within the signal coverage area.
7. What are the disadvantages of AM and FM?
AM disadvantages:
- Highly susceptible to noise and interference.
- Poor audio quality, especially for music.
- Lower bandwidth efficiency.
- Requires more bandwidth compared to AM.
- Effective only for shorter transmission ranges.
- Complex receiver circuits.
8. List the uses of AM and FM.
Both AM and FM are used for different applications:
- AM: News radio, talk shows, sports broadcasting, aviation communication, long-distance communication.
- FM: Music broadcasting, local radio stations, TV sound transmission, two-way radio (walkie-talkies).
9. How do noise and interference affect AM and FM signals?
AM signals are more affected by noise and interference because they depend on amplitude, which can easily be distorted:
- Static and electrical disturbances can degrade audio quality.
- FM signals are more resistant because information is carried by frequency, not amplitude.
- FM provides more consistent and clear sound in noisy environments.
10. What is the bandwidth required for AM and FM?
The bandwidth requirements differ between AM and FM:
- AM stations: Typically require twice the audio frequency being transmitted (e.g., 10 kHz for an audio signal of 5 kHz).
- FM stations: Usually require a much wider bandwidth (around 200 kHz or more), enabling higher audio fidelity.
