S331L UG PN: 10580-00321 Rev. M B-5
Glossary of Terms B-2 Glossary Terms
CPM : Continuous Phase Modulation (CPM) is a phase
modulation technique employing smooth
transitions between signal states. This reduces
sidelobe spectral energy and improves co-channel
performance.
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 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.
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