S820E UG PN: 10580-00343 Rev. H C-7
Glossary C-2 Glossary Terms
DANL : Displayed Average Noise Level (DANL): Displayed
average noise level is sometimes confused with the term
Sensitivity. While related, these terms have different
meanings. Sensitivity is a measure of the minimum
signal level that yields a defined signal-to-noise ratio
(SNR) or bit error rate (BER). It is a common metric of
radio receiver performance. Spectrum analyzer
specifications are always given in terms of the DANL.
One of the primary uses of a spectrum analyzer is to
search out and measure low-level signals. The
limitation in these measurements is the noise
generated within the spectrum analyzer itself. This
noise, generated by the random electron motion in
various circuit elements, is amplified by multiple gain
stages in the analyzer and appears on the display as a
noise signal. On a spectrum analyzer, this noise is
commonly referred to as the Displayed Average Noise
Level, or DANL 1. While there are techniques to
measure signals slightly below the DANL, this noise
power ultimately limits our ability to make
measurements of low-level signals.
dB : Decibel or deciBel (dB) is a logarithmic ratio of the
difference between two values (a logarithm ratio is
equal to 10 times). dB is a unit for measuring relative
power ratios in terms of gain or loss. The units of dB are
expressed in terms of the logarithm to base 10 of a ratio
and typically are expressed in watts. For example, a
-3dB loss indicates a 50% loss in power; a +3dB reading
is a doubling of power; 10 dB indicates an increase (or a
loss) by a factor of 10; 20 dB indicates an increase (or a
loss) of a factor of 100; 30 dB indicates an increase (or a
loss) by a factor of 1000. Common values of dB
expressed in ratios: 0 dB = 1:1, 10 dB = 10:1, 20 dB =
100:1, 30 dB = 1000:1, -30 dB = 0.001:1 [or (1/1000):1].
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