McDewey

Noise Measurement Units In addition to the description of test−tone power at various points in a circuit, decibel−related units of measure can be used to describe noise present in a circuit. dBrn In order to describe power in a circuit, the term dBm is used, meaning "power referenced to 1 mW." Since noise typically contains much less than 1 mW of power, it is convenient to use a reference power that is much smaller than 1 mW. The reference power used in the description of noise is 90 dBm. The notation used to describe noise in terms of reference noise is dBrn. If you know the noise level in dBm, you can easily measure the noise in dBrn: dBrn = dBm + 90 dB For example, a noise measurement of 30 dBrn indicates a power level of ž0 dBm (30 dB above the 90 dBm reference noise level). This table shows the relationship between dBm0 and dBrn. dBm0 dB Value 0 90 −10 80 −20 70 −30 60