bandwidth

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bandwidth

1. The range of frequencies over which an instrument, such as a radio telescope, is sensitive. A wide bandwidth gives good sensitivity to sources that emit over a wide range of frequencies (e.g. by synchrotron emission), whereas a narrow bandwidth gives good sensitivity to spectral lines.
2. (coherence bandwidth) The range of frequencies over which electromagnetic or other emissions from a source maintain coherence.

bandwidth

[′band‚width]
(communications)
The difference between the frequency limits of a band containing the useful frequency components of a signal.
A measure of the amount of data that can travel a communications path in a given time, usually expressed as thousands of bits per second (kbps) or millions of bits per second (Mbps).

bandwidth

(communications)
The difference between the highest and lowest frequencies of a transmission channel (the width of its allocated band of frequencies).

The term is often used erroneously to mean data rate or capacity - the amount of data that is, or can be, sent through a given communications circuit per second.

bandwidth

(1) Computer people may use the term for capability and time. For example, "not enough bandwidth to get the job done" means not enough staff or time to do it. Its true meaning follows.

(2) The transmission capacity of an electronic pathway such as a communications line, computer bus or computer channel. Digital bandwidth is the number of pulses per second measured in bits per second (bps). For example, Ethernet transmits at different speeds, including 10 Mbps, 100 Mbps and 1000 Mbps (see Mbps and baseband).

When transmitting alternating frequencies, as with all wired analog, many wired digital and most wireless communications, the bandwidth is the difference between the highest and lowest frequencies, measured in cycles per second, or Hertz (Hz). For example, 802.11n Wi-Fi transmits in 20 MHz and 40 MHz channels within the 2.4 GHz and 5 GHz bands. The 20 and 40 MHz channel frequencies are the bandwidths, and each channel is divided into subchannels.

From Hertz to Bits - A Complicated Process
When using alternating frequencies for digital transmission, the frequencies are modified (modulated) by the digital input. Using the 802.11n Wi-Fi example, the resulting bit rate can range from 6.5 Mbps to 600 Mbps. This extremely wide range is determined by the signal strength and interference in the environment at any given moment. Any one of more than 30 combinations of channel bandwidth (20, 40 MHz), modulation scheme, error correction rate, channel spacing and number of antennas may be selected, on a packet-by-packet basis. See modulation, video bandwidth, space/time and bandwidth junkie.


Bandwidth in Hertz to Bandwidth in Bits
This quadrature PSK (QPSK) example is one of the simplest modulation schemes. Each set of two input bits modifies the carrier into four phase angles. The amplitude remains constant, unlike QAM modulation, in which the amplitude is varied (see QAM).











References in periodicals archive ?
In units of the band width, the corresponding Green function for complex energy with negative real part has the form
The Global Electromagnetic Spectrum Information System, a new high-tech database, will go a long way toward getting the most out of the military's band width, Atkins said.
The missing link to broadband all along has been balancing the external band width availability with the internal bandwidth demand.
There's something about band widths that is very much like money, sex and power.
Band width, which limits the amount of data that can be moved, will need to expand to that provided by fiber optics for effective use of the evolving technologies.
White Noise -- A noise whose spectrum (level) density is substantially indenpendent of frequency over a specified range and has equal power for any range of frequencies of constant band width.
Hercules has also developed technology for adding single prepreg tows and varying the band width while ply thickness remains constant, thus allowing the fabrication of parts with varying cross-sections and constant thickness.
Tenders are invited for High band width data acquisition system
Wide signal band width at RF, 0 dBm output, low noise and serial bus control delivers desirable flexibility and performance, all at a low operating power.
We, therefore, observed changes in band width.""In previous studies, electron donor or acceptor metals were used to change energy gap of metallic oxides leading to increase in costs and efforts.
The Optocator 2201 is being enhanced with a high frequency data acquisition system that will increase the speed of the sensor to a 32 kHz sample rate and 8 kHz band width.
The unit's wide band width coupled with its high power output allows it to be used in both EMC and communications applications.