## Tuesday, November 6, 2018

### Convert Watt or mWatt to dB or dBm

This post is merely to remind me. So, I just copy paste from here.

But, first of all, here is the formula to convert dB to Watt

`watts = 10^((dbm-30)/10)`

Then, let's read the explation for corveting from Watt or mWatt to dB or dBm.

The dB Conversion block converts a linearly scaled power or amplitude input to dB or dBm. The reference power is 1 Watt for conversions to dB and 1 mWatt for conversions to 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 output is the same size 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 ```
The dBm conversion is equivalent to performing the dB operation after converting the `(abs(u)^2/R)` result to milliwatts.

## Parameters

Convert to
The logarithmic scaling to which the input is converted, `dB` or `dBm`. The reference power is 1 W for conversions to dB and 1 mW for conversions to dBm. Tunable(Simulink).
Input signal
The type of input signal, `Power` or `Amplitude`.
When selected, adds `eps` to all input values (power or voltage). Tunable (Simulink).