The symbol dBrn or dB is an abbreviation for decibels above reference noise

Reference noise

In telecommunication, reference noise is the magnitude of circuit noise chosen as a reference for measurement.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.Specific ones include: dBa, dBa, dBa,...

.

Weighted noise power

Noise power

In telecommunication, the term noise power has the following meanings:# The measured total noise per bandwidth unit at the input or output of a device when the signal is not present.# The power generated by a random electromagnetic process....

 in dB is referred to 1.0 picowatt. Thus, 0 dBrn = -90 dBm

DBm

dBm is an abbreviation for the power ratio in decibels of the measured power referenced to one milliwatt . It is used in radio, microwave and fiber optic networks as a convenient measure of absolute power because of its capability to express both very large and very small values in a short form...

. Use of 144 line

Line (electrical engineering)

In electrical engineering, a line is, more generally, any circuit of an electrical system. This electric circuit loop , consists of electrical elements connected directly by conductor terminals to other devices in series....

, 144-receiver, or C-message weighting, or flat weighting

Flat weighting

Flat weighting: In a noise-measuring set, a noise weighting based on an amplitude-frequency characteristic that is flat over a frequency range that must be stated.Note 1: Flat noise power is expressed in dBrn or in dBm...

, can be indicated in parentheses.

With C-message weighting, a one-milliwatt, 1000 Hz

Hertz

The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....

 tone will read +90 dBrn, but the same power as white noise

White noise

White noise is a random signal with a flat power spectral density. In other words, the signal contains equal power within a fixed bandwidth at any center frequency...

, randomly distributed over a 3 kHz band will read approximately +88.5 dBrn, because of the frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 weighting.

With 144 weightings, a one milliwatt, 1000 Hz white noise tone will also read +90 dBrn, but the same 3 kHz power will only read +82 dBrn, because of the different frequency weighting.