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44 Cards in this Set
- Front
- Back
Frequency |
Number of times the signal makes a complete up and down cycle in 1 second |
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Phase |
A measure of shift of a signal in time relative to the start of a cycle |
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Wavelength |
Measure of the physical distance that a wave travels over one complete cycle |
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Amplitude |
The height from the top peak to the bottom peak of the signals waveform |
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Law of zero |
A value of 0 db means that two absolute power values are equal |
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Law of 3s |
A value of 3 db means that the power value of interest is double the reference value. A value of -3 means the power value of interest is half the reference. |
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Law of 10s |
A value of 10db means that the power value of interest is 10 times the reference value. A value of -10db means the power value of interest is 1/10 of the reference. |
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EIRP |
Effective isotrophic radiated power - actual power level radiated from the antenna. |
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RSSI |
Recieved signal strength indicator - receiving end of the signal. Receivers measure a signals power in dBm according to the RSSI scale |
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Noise floor |
The average signal strength of the noise. |
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SNR |
Signal to Noise ratio - the difference between the signal and the noise, measired in dB. Calculation is signal minus noise floor...20dB SNR is minimum to work. Ex: signal is -54dBm. Noise is -90dBm -54 - (-90) = 36dB = SNR |
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Band |
A contiguous range of frequencies |
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Bandwidth |
A range of frequencies used by a single channel or a single RF signal |
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Barker 11 code |
An 11 bit sequence of encoded bits that represent a single data bit |
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BSS |
Basic Service Set - Wireless service provided by an AP to one or more associated clients. |
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Carrier signal |
The basic, steady RF signal that is used to carry other useful information |
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Channel |
An arbitrary index that points to a specific frequency in a band |
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Chip |
A bit produced by a coder |
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Coder |
A function that converts data bits into multiple encoded bits before transmission, to provide resilience against noise and interference. |
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CCK |
Complimentary Code Keying: An encoding method that takes either 4 or 8 data bits at a time to create a 6bit or 8bit symbol. The symbols are fed into DQPSK to modulate the carrier signal. |
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dB |
Decibal: A logarithmic function that compares one absolute measurement to another |
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dBd |
The gain of an antenna, measured in dB, as compared to a simple dipole antenna. |
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dBi |
The gain of an antenna, measured in dB, as compared to an isotrophic reference antenna. |
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dBm |
The power level of a signal, measured in dB, as compared to a reference signal power of 1 milliwatt. |
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Demodulation |
The recievers process of interpreting changes in the carrier signal to recover the original information being sent. |
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DBPSK |
Differential binary phase shift keying: A modulation method that takes 1 bit of encoded data and changes the phase of the carrier signal in one of two ways. |
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DQPSK |
Differential quadrature phase shift keying: A modulation method that takes 2 bits of encoded data and changes the phase of the carrier signal in one of four ways. |
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DSSS |
Direct sequence spread spectrum: A wireless lan method where a transmitter uses a single fixed, wide channel to send data. |
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FHSS |
Frequency hopping spread spectrum: A wireless lan method where a transmitter "hops" between frequencies all across a band. |
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Hertz |
A unit of frequency equaling one cycle per second |
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In phase |
The condition when the cycles of two identical signals are in sync with each other |
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Isotrophic antenna |
An ideal, theoretical antenna that radiates RF equally in every direction |
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Link budget |
Cumulative sum of gains and losses measured in dB over the complete RF signal path; a transmitters power level must overcome the link budget so that the signal can reach a receiver effectively. |
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Modulation |
The transceivers process of altering the carrier signal according to some other information source. |
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Narrow band |
RF signals that use a very narrow range of frequencies. |
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Noise floor |
The average power level of noise measured at a specific frequency |
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OFDM |
Orthogonal frequency-division multiplexing: Data transmission method that sends data bits in parrallel over multiple frequencies within a single 20 mhz wide channel. Each frequency represents a single subcarrier |
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Out of phase |
The condition when the cycles of one signal are shifted in time in relation to another signal |
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Phase |
A measure of shift in time relative to the start of a cycle; ranges between 0 and 360 degrees |
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QAM |
Quadrature amplitude modulation: A modulation method that combines QPSK phase shifting with multiple amplitude levels to produce a greater number of unique changes to the carrier signal. The number of preceding the QAM name designates hiw many carrier signal changes are possible. |
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RF |
Radio frequency: The portion of the frequency spectrum between 3khz and 300ghz |
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Sensitivity level |
The RSSI threshold (in dBm) that divides unintelligible RF signals from useful ones |
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Spread spectrum |
RF signals that spread the information being sent over a wide range of frequencies. |
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Symbol |
A complete group of encoded chips that represents a data bit. |