# Source code for deltasigma._dbm

# -*- coding: utf-8 -*-
# _dbm.py
# This module provides the dbm function.
# This file is part of python-deltasigma.
#
# python-deltasigma is a 1:1 Python replacement of Richard Schreier's
# MATLAB delta sigma toolbox (aka "delsigma"), upon which it is heavily based.
# The delta sigma toolbox is (c) 2009, Richard Schreier.
#
# python-deltasigma is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# LICENSE file for the licensing terms.

"""This module provides the dbm() function, used to convert an RMS voltage to dBm.
"""

from __future__ import division

import numpy as np

from ._utils import carray, restore_input_form, save_input_form

[docs]def dbm(v, R=50):
"""Calculate the dBm equivalent of an RMS voltage v.

.. math::

P_{dBm} = 10 \\mathrm{log}_{10}(1000 \\frac{v^2}{R} )

**Parameters:**

v : scalar or sequence
The voltages to be converted.

R : scalar, optional
The resistor value the power is calculated upon, defaults to 50 ohm.

**Returns:**

PdBm : scalar or sequence
The input in dBm.

.. seealso:: :func:undbm, :func:db, :func:dbp, :func:dbv

"""
iform = save_input_form(v)
v = carray(v)
y = -np.Inf * np.ones(np.size(v))
nonzero = (v != 0)
y[nonzero] = 10. * np.log10(np.abs(v[nonzero] ** 2.) / R) + 30
return restore_input_form(y, iform)