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The modulation index (or modulation depth) of a modulation scheme describes by how much the modulated variable of the carrier signal varies around its unmodulated level. It is defined differently in each modulation scheme. Amplitude modulation index; Frequency modulation index; Phase modulation index
Carrier wave - Wikipedia
For a sine wave modulation, the modulation index is seen to be the ratio of the peak frequency deviation of the carrier wave to the frequency of the modulating sine wave. If h ≪ 1 {\displaystyle h\ll 1} , the modulation is called narrowband FM (NFM), and its bandwidth is approximately 2 f m {\displaystyle 2f_{m}\,} .
Waterfall plot of a 146.52 MHz radio carrier, with amplitude modulation by a 1,000 Hz sinusoid. Two strong sidebands at + and - 1 kHz from the carrier frequency are shown. A carrier, frequency modulated by a 1,000 Hz sinusoid. The modulation index has been adjusted to around 2.4, so the carrier frequency has small amplitude. Several strong ...
Angle modulation is a class of carrier modulation that is used in telecommunications transmission systems. The class comprises frequency modulation (FM) and phase modulation (PM), and is based on altering the frequency or the phase , respectively, of a carrier signal to encode the message signal.
is the peak frequency deviation; is the highest frequency in the modulating signal. For example, a typical VHF/UHF two-way radio signal using FM mode, [2] with 5 kHz peak deviation, and a maximum audio frequency of 3 kHz, would require an approximate bandwidth of 2 × (5 kHz + 3 kHz) = 16 kHz.
The carrier frequency is 1800 Hz, meaning that the lower cut off frequency is 1,800 − 1,200/2 = 1,200 Hz, and the upper cutoff frequency is 1,800 + 1,200/2 = 2,400 Hz. A V.34 modem may transmit symbols at a baud rate of 3,420 Bd, and each symbol can carry up to ten bits, resulting in a gross bit rate of 3420 × 10 = 34,200 bit/s.
The carrier is an RF signal, typically of microwave frequencies, which is usually (but not always) modulated to allow the system to capture the required data. In simple ranging radars, the carrier will be pulse modulated and in continuous wave systems, such as Doppler radar, modulation may not be required.