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Frequency-shift keying
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave.
Phase-shift keying
Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). Any digital modulation scheme uses a finite number of distinct signals to represent digital data. PSK uses a finite number of phases, each assigned a unique pattern of binary bits.
8-DPSK
Qaudraturephase-shift keying
Sometimes known as quaternary or quadriphase QPSK uses four points on the constellation diagram, equispaced around a circle. With four phases, QPSK can encode two bits per symbol shown in the diagram.
Although QPSK can be viewed as a quaternary modulation, it is easier to see it as two independently modulated quadrature carriers. With this interpretation, the even (or odd) bits are used to modulate the in-phase component of the carrier, while the odd (or even) bits are used to modulate the quadraturephase component of the carrier.
QPSK constellation diagram
Quadrature amplitude modulation
Quadrature amplitude modulation (QAM) is a modulation scheme which conveys data by changing (modulating) the amplitude of two carrier waves. These two waves, usually sinusoids, are out of phase with each other by 90 and are thus called quadraturecarriers - hence the name of the scheme.
QAM is a combination of the phase domain. The number of possible states = 360/number of phase changes used. The demodulation process for this becomes quite complex, but is not unachievable with modern technology. It is used frequently in high-capacity data point-to-point radio links. 64QAM, 128QAM, 256QAM and even 518QAM are not uncommon.
modem detector demodulator modulator frequency phase amplitude carrier signal sinusoid waveform tone periodic waveform modulation oscillator
List of words
filter waveform throughput rate
spectral efficiency frequency of operation range of propagation pulse
keying relationship
amplitude modulation vestigial sideband modulation index depth of modulation instantaneous frequency modulation
sideband signal-to-noise ratio
List of words
voltage-controlled oscillator |
phase modulation |
pass-band filter |
Baud |
low-pass filter |
frequency modulation |
on-off keying |
frequency deviation |
constellation diagram |
wideband |
bit rate |
narrowband |
symbol rate |
amplitude-shift keying |
position |
odd |
superimposed |
even |
|
quaternary |
|
phase-shift keying |
|
complex plane |
List of words (abbreviations)
Public Switched Telephone Network (PSTN)
Phased Locked Loop (PLL)
Voltage Controlled Oscillator (VCO)
Radar Principle
Radar is an acronym for
Radio Detecting and Ranging
Radar uses electromagnetic energy pulses. The radio-frequency (RF) energy is transmitted to and reflected from the reflecting object. A small portion of the reflected energy returns to the radar set. This returned energy is called an echo, just as it is in sound terminology. Radar sets use the echo to determine the direction and distance of the reflecting object.
Distance Determination
The distance is determined from the running time of the high-frequency transmitted signal and the propagation c0. The actual range of a target from the radar is known as slant range. Since the waves travel to a target and back, the round trip time is divide by two in order to obtain the time the wave took to reach the target.
Slant range: R=c0 ·t/2
c0 - speed of light (3·108 m/s), t - measured time [s], R - slant range [m].
The factor of two in the formula comes from the observation that the radar pulse must travel to the target and back before detection, or twice the range.