May 24, 2018  

dbm to watts conversion for radio, radar and microwaves 

Decibels and dbmDecibels are used to represent the ratio of two quantities of power: db = 10 log P_{1}/P_{0} . In the case of dbm the reference power P_{0} is 1 milliwatt : dbm = 10 log P_{1}/1mw. Inverting this equation gives the power in terms of the reference power: P_{1}= P_{0}10^{db/10}. In the case of dbm the equation is P_{1}= 1mw·10^{dbm/10}.Why? It is not unusual in a radio, radar, or microwave system to have 100,000 watts of transmit power, 1 microwatt of receive power, and various gains and losses from antennas, distance, and absorbing media. Adding and subtracting db is more convenient than multiplying, particularly if you are using a slide rule and trying to keep track of the decimal point. For signals on a wire it is much easier to measure volts or amps with a voltmeter or current probe, but dbm can still be used. Since Watts are proportional to Amps squared or Volts squared, db (in power) = 20 log V_{1}/V_{0} or db = 20 log I_{1}/I_{0} . This is only useful in cases where the voltage or current is measured at the same impedance or resistance, which allows the ratio of two powers I^{2}R or V^{2}/R to cancel out the R.
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