AM vs. FM
- Carrier Wave (Carrier)
- In telecommunications, a carrier wave, or carrier is a waveform (usually sinusoidal) that is modulated (modified) with an input signal for the purpose of conveying information. This carrier wave is usually of much higher frequency than the input signal. The purpose of the carrier is to transmit the information through space as an electromagnetic wave.
- Amplitude Modulation
- Carrier Wave is modified by varying amplitude based on the volume and pitch of the input signal
- Power inefficient (2/3rds lost to Carrier Wave)
- Transmits two sidebands of equal bandwidth, which are mirror images of each other
- Power can be enhanced by eliminating one sideband (SSB)
- Power can further be enhanced by suppressing carrier power
- When the carrier is missing, a BFO (beat frequency oscillator) must be used to recreate it on the receiving end
- Frequency Modulation
- Carrier Wave is modified by varying frequency based on the volume and pitch of the input signal
- Requires wider signal bandwidth than AM
- More resistant to noise and interference
- Better sound reproduction
- Because FM has wider bandwidth it was used for high fidelity FM radio (really VHF radio)
- Lower frequency AM radio signals may propagate at night due to F-layer skip
- Frequency and transmission mode do not correlate
- Other modes are possible: SSB, F (or P) SK, CW (Morse Code)
- Communication proven from below 9kHz to above 10GHz
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