. Addition of information to an electronic carrier signal.
. Carrier Signal: Signal with constant amplitude and frequency.
. Information can be added to carrier by varying its amplitude, frequency, phase.
. Carrier Signal: Signal with constant amplitude and frequency.
. Information can be added to carrier by varying its amplitude, frequency, phase.
Need of Modulation:
. To transmit signals over larger distances.
. To allow smaller antennas (for low frequency signals).
. To reduce attenuation (low frequency signals).
. Used in Radio, Lasers, Computer networks.
. Can be applied to Alternating Current and Direct Current.
. Used in Radio, Lasers, Computer networks.
. Can be applied to Alternating Current and Direct Current.
Types of Modulation:
Amplitude Modulation(AM):
. First successfully carried out in 1870 to produce quality radio over telephone lines.
. Amplitude of carrier signal is varied.
. Amplitude of carrier signal is varied.
. Frequency and Phase are kept constant.
. Transmits information over larger distances.
. Transmits information over larger distances.
. It is simple to implement.
. Used in News broadcasting.
. Used in Aircrafts for communication between station and pilot and vice-versa.
. Information is on the edges of signal (Amplitude).
. Not suitable for Music broadcasting because it more prone to interference.
. Used in News broadcasting.
. Used in Aircrafts for communication between station and pilot and vice-versa.
. Information is on the edges of signal (Amplitude).
. Not suitable for Music broadcasting because it more prone to interference.
Frequency Modulation(FM):
. Frequency of carrier signal is varied.
. Amplitude and Phase are kept constant.
AM Vs FM:
Property | AM | FM |
---|---|---|
Origin | 1870 | 1933 |
Transmission | Amplitude varies, Frequecy constant | Frequency varies, Amplitude constant |
Frequency range | 535-1705 KHz | 88-108MHz |
Bandwidth | 30KHz | 80KHz |
Rate | 1200 bits/sec | 1200-2400 bits/sec |
Coverage | Larger | Smaller |
How it trasmits? | By changing signal strength | By changing frequency of signal |
Interference | More | Less |
Sound quality | Poor | Good |
Used for: | News programming, radio | Music channels |
Radio Stations in world: | 16,265 | 28,693 |