dBm0 is an abbreviation for the power in
dBm
DBM or dbm may refer to:
Science and technology
* dBm, a unit for power measurement
* DBM (computing), family of key-value database engines including dbm, ndbm, gdbm, and Berkeley DB
* Database Manager (DBM), a component of 1987's ''Extended Edi ...
measured at a
zero transmission level point.
dBm0 is a concept used (amongst other areas) in audio/telephony processing since it allows a smooth integration of analog and digital chains. Notably, for A-law and μ-law codecs the standards define a sequence which has a 0 dBm0 output.
Note 1: A consequence for the
A-law
An A-law algorithm is a standard companding algorithm, used in European 8-bit PCM digital communications systems to optimize, i.e. modify, the dynamic range of an analog signal for digitizing. It is one of two versions of the G.711 standar ...
and
μ-law codecs of the 0 dBm0 definition is that they have a respective 3.14 dBm0 and 3.17 dBm0 maximum signal level (ratio between the maximum obtainable sine wave amplitude and the specified reference 0 dBm0 sine wave amplitude).
Note 2: 0 dBm0 is often replaced by or used instead of
digital milliwatt or
zero transmission level point.
The "unit" dBm0 is used to describe levels of digital signals. E.g. the nominal downlink level in mobile phone telecommunication at the point of interconnection (POI) is -16 dBm0. The unit is derived from its counterpart dBm. Even though digitally represented signals have nothing to do with absolute power levels and cannot be expressed as dBm, the dinosaurs of telephonometrie had problems thinking in levels relative to full scale, so they introduced the completely redundant pseudo-digital unit of "dBm0". It actually connects both, the old world of analogue telecommunication and the new world of digital communication in a weird and unnatural way. The 0 dBm0 level corresponds to the
digital milliwatt (DMW) and is defined as the absolute power level at a digital reference point of the same signal that would be measured as the absolute power level, in dBm, if the reference point was analog.
The absolute power in dBm is defined as 10 log (power in mW/1 mW). When the test impedance is 600 Ω resistive, 0 dBm can be referred to a voltage of 775mV, which results in a reference active power of 1 mW. 0 dBm0 corresponds to an overload level of approximately 3 dBm in the A/D conversion.
Given a sine signal of
RMS voltage of 0.775
the Power at
ZLP in
is: