- Industry: Telecommunications
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The magnitude of the radial component of velocity of an object, i.e., a target, relative to a radar site, that cannot be measured by the radar unit. Note: Radar blind speeds occur because of the relationship between the transmitted pulse repetition rate (PRR) and the received pulse-repetition rate. The Doppler pulse repetition rate is the difference between the transmitted and received pulse repetition rates. For example, when the object is stationary with respect to the radar site, the reflected PRR is the same as the transmitted PRR and therefore a net zero signal is indicated for the radial component of velocity. If it happens that the Doppler PRR is the same as the transmitted PRR, i.e., the illuminating PRR, or it is a multiple of the transmitted PRR, a zero signal is also obtained and hence the radar is blind to these speeds, one for each multiple of the transmitted pulse repetition rate. It is not the absolute magnitude of the speed of the object that is measured, but only the radial component of the speed. The radial components of blind speeds, vm, are given by vm = mf/102, where v is the blind speed in knots, m is the multiple of the radar pulse repetition rate and the number of the blind speed, namely a positive integer, 1, 2, 3, 4,. . . , for the first, second, third, fourth, and so on, blind speed, is the wavelength of the illuminating radar in centimeters; f is the transmitter pulse repetition rate in pps (pulses per second); and the 102 is a units conversion factor.
Industry:Telecommunications
The magnitude of circuit noise chosen as a reference for measurement. Note: Many different levels with a number of different weightings are in current use, and care must be taken to ensure that the proper parameters are stated. See dBa, dBa0, dBm, dBm0, dBrn, dBrnC, dBrnC0, dBx.
Industry:Telecommunications
The magnitude of a pulse parameter, such as the field intensity, voltage level, current level, or power level. Note 1: Pulse amplitude is measured with respect to a specified reference and therefore should be modified by qualifiers, such as "average," "instantaneous," "peak," or "root-mean-square. " Note 2: Pulse amplitude also applies to the amplitude of frequency- and phase-modulated waveform envelopes.
Industry:Telecommunications
The magnetized portion along the length of a videotape on which synchronous control information is placed; the control track contains a pulse for each video field and is used to synchronize the tape and the video signal.
Industry:Telecommunications
The machine identification of printed characters through use of light-sensitive devices.
Industry:Telecommunications
The luminous intensity in a specified direction, of a monochromatic source which has a frequency of 540 x 1012 Hz and which has a radiant intensity, in the specified direction, of (1/683) watt per steradian.
Industry:Telecommunications
The lowest order mode of a waveguide. Note: In optical fibers, the fundamental mode is designated LP01 or HE11.
Industry:Telecommunications
The lowest modulation frequency at which the RMS peak-to-valley amplitude (optical power) difference of an intensity-modulated monochromatic signal decreases, at the output of the fiber, to a specified fraction (usually one-half) of the RMS peak-to-valley amplitude (optical power) difference of a nearly-zero (arbitrarily low) modulation frequency, both modulation frequencies having the same RMS peak-to-valley amplitude (optical power) difference at the fiber input. Note 1: In multimode fibers, multimode distortion is usually the most significant parameter limiting fiber bandwidth, although material dispersion may also play a significant role, especially in the first (850-nm) window. Note 2: In multimode fibers, the bandwidth•distance product (loosely, "fiber bandwidth") is customarily specified by vendors for the bandwidth as limited by multimode distortion only. The spectral width of the optical source is assumed to be extremely narrow. In practice, the effective fiber bandwidth will also be limited by dispersion, especially in the first (850-nm) window, where material dispersion is relatively high, because optical sources have a finite spectral width. Laser diodes typically have a spectral width of several nanometers, FWHM. LEDs typically have a spectral width of 35 to 100 nm, FWHM. Note 3: The effective risetime of multimode fibers may be estimated fairly accurately as the square root of the sum of the squares of the material-dispersion-limited risetime and the multimode-distortion-limited risetime. Note 4: In single-mode fibers, the most important parameters affecting fiber bandwidth are material dispersion and waveguide dispersion. Practical fibers are designed so that material dispersion and waveguide dispersion cancel one another at the wavelength of interest. Note 5: Regarding effective fiber bandwidth as it affects overall system performance, it should be recognized that optical detectors such as PIN diodes are square-law devices. Their photocurrent is proportional to the optical power of the detected signal. Because electrical power is a function of the square of the current, when the optical power decreases by one-half (a 3-dB decrease,) the electrical power decreases by three-fourths (a 6-dB decrease. ) 2. Loosely, synonym bandwidth•distance product.
Industry:Telecommunications
The level of acoustic noise existing at a given location, such as in a room, in a compartment, or at a place out of doors. Note 1: Ambient noise level is measured with a sound level meter. Note 2: Ambient noise level is usually measured in dB above a reference pressure level of 0. 00002 Pa, i.e., 20 Pa (micropascals) in SI units. A pascal is a newton per square meter. Note 3: In the centimeter-gram-second system of units, the reference level for measuring ambient noise level is 0. 0002 dyn/cm2. Synonym room noise level.
Industry:Telecommunications
The lowest level of abstraction within the OSI standards scheme. Note: Each OSI--Protocol Specification operates at a single layer. Each defines the primitive operations and permissible responses required to exchange information between peer processes in communicating systems to carry out all or a subset of the services defined within the OSI--Service Definitions for that layer.
Industry:Telecommunications
