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Ratio Modes: Eb/No: This is the most commonly used ratio for systems using digital modulation. Most digital modulation schemes are conventionally specified in terms of theoretical BER vs Eb/No performance. Modems typically have a spec in which actual performance must be within some amount of theoretical. Eb is calculated by the following expression:
The CNG requires the operator to enter in the data rate. The CNG measures the signal power, normalizes it to the output port and displays the results. The user enters in the desired ratio and the instrument automatically makes the conversion using Eqn 2. As both Eb and No are expressed in units of dBm/Hz, the ratio is dimensionless and is expressed simply in dB. Typical testing requires set ratios in the range of 3 to 12 dB. C/N Mode: This mode of operation is traditionally used in analog radios where N is the receiver or channel noise equivalent bandwidth. In this mode, the operator enters in the noise equivalent bandwidth of the channel under test. The operator then enters in the desired ratio of the carrier power C to the noise power N in this channel bandwidth. The CNG automatically normalizes the noise to the user’s entered channel bandwidth to achieve the correct ratio. Mathematically, the expression is:
As in Eb/No mode, the ratio is dimensionless and is expressed simply in dB. Typical ratio ranges are in the range of 10 to 40 dB. C/No Mode: In this mode, there are no operator dependant variables. The C is measured and No is independent of bandwidth. As C is in units of power in dBm and No is in units of spectral density or dBm/Hz, the ratio is not dimensionless and in decibel form is expressed as dB*Hz.
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Intro Page The Micronetics Difference cont. Ratio Modes
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