C-2 Glossary Glossary of Terms
C-6 PN: 10580-00252 Rev. K Site Master User Guide
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 -3 dB loss indicates a
50% loss in power; a +3 dB 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].
dBc : Decibels referenced to the carrier (dBc) is a technique for expressing a
power measurement in logarithmic form using the carrier power as a
reference. The units are used to describe how far down signals and noise
are relative to a known signal. Typical use of this term is to describe
spurious signals and noise compared to a desired transmit signal.
dBd : Decibels referenced to a dipole antenna (dBd) is a technique for
expressing a power gain measurement in logarithmic form using a
standard dipole antenna as a reference. dBd is a measurement of signal
gain used in radio antenna design. Pecifically, dBd referrs to signal gain
in a dipole radiator.
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