User`s guide

dB Conversion
5-118
5dB Conversion
Purpose Convert magnitude data to decibels (dB or dBm).
Library Math Functions / Math Operations
Description The dB Conversion block converts a linearly scaled power or amplitude input
to dB or dBm. The
Input signal parameter specifies whether the input is a
power signal or a voltage signal, and the
Convert to parameter controls the
scaling of the output. When selected, the
Add eps to input to protect
against “log(0) = -inf”
parameter adds a value of eps to all power and voltage
inputs. When this option is not enabled, zero-valued inputs produce
-inf at the
output. The size and frame status of the output are the same as the input.
Power Inputs
Select Power as the Input signal parameter when the input, u, is a real,
nonnegative, power signal (units of watts). When the
Convert to parameter is
set to
dB, the block performs the dB conversion
y = 10*log10(u) % Equivalent MATLAB code
When the Convert to parameter is set to dBm, the block performs the dBm
conversion
y = 10*log10(u) + 30
The dBm conversion is equivalent to performing the dB operation after
converting the input to milliwatts.
Voltage Inputs
Select Amplitude as the Input signal parameter when the input, u, is a real
voltage signal (units of volts). The block uses the scale factor specified in ohms
by the
Load resistance parameter, R, to convert the voltage input to units of
power (watts) before converting to dB or dBm. When the
Convert to parameter
is set to
dB, the block performs the dB conversion
y = 10*log10(abs(u)^2/R)
When the Convert to parameter is set to dBm, the block performs the dBm
conversion
y = 10*log10(abs(u)^2/R) + 30