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Chemical shift δ is usually expressed in parts per million (ppm) by frequency, because it is calculated from [5] =, where ν sample is the absolute resonance frequency of the sample, and ν ref is the absolute resonance frequency of a standard reference compound, measured in the same applied magnetic field B 0.
The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. [ 1 ] [ 2 ] [ 3 ] The Doppler effect is named after the physicist Christian Doppler , who described the phenomenon in 1842.
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in ...
If the shift in is expressed as a fraction of the period, and then scaled to an angle spanning a whole turn, one gets the phase shift, phase offset, or phase difference of relative to . If F {\displaystyle F} is a "canonical" function for a class of signals, like sin ( t ) {\displaystyle \sin(t)} is for all sinusoidal signals, then φ ...
The perturbation of this alignment of the nuclear spins by a weak oscillating magnetic field, usually referred to as a radio-frequency (RF) pulse. Detection and analysis of the electromagnetic waves emitted by the nuclei of the sample as a result of this perturbation. Similarly, biochemists use NMR to identify proteins and other complex ...
Frequency mixer symbol used in schematic diagrams. A heterodyne is a signal frequency that is created by combining or mixing two other frequencies using a signal processing technique called heterodyning, which was invented by Canadian inventor-engineer Reginald Fessenden.
Regardless, radars that employ the technique are universally coherent, with a very stable radio frequency, and the pulse packets may also be used to make measurements of the Doppler shift (a velocity-dependent modification of the apparent radio frequency), especially when the PRFs are in the hundreds-of-kilohertz range. Radars exploiting ...
In order to reduce the interference from the fringe area transmitters transmitting in the same channels, a method named frequency offset is often used. By this method, a slightly shifted RF is assigned for a transmitter which may experience interference from other transmitters. In TV transmission, the shifted RF is calculated by the formula;