To convert a power ratio to dB, the formula is 10 log Po/Pi. For example,
if you had an amplifier that took 2 watts input and provided 40 watts
output, that ratio is 40/2 = 20. The common logarithm (base 10) of 20 is
1.30..., and multiply that by 10 and you get 13.01 dB gain.
Likewise, if you have a repeater where the power input to the duplexer is
100 watts, and you measure 73 watts at the output of the duplexer, the
power ratio is 73/100 or 0.73. The log of 0.73 is -0.137. Multiply that
by 10 and you get -1..37 dB. This is a gain of -1.37 dB, which we normally
refer to as a loss of 1.37 dB.
The ARRL Handbook and the ARRL Antenna Book both have excellent tutorials
about working with decibels. Note that the "B" is capitalized because the
Bel is an SI unit named in honor of Alexander Graham Bell.
73, Eric Lemmon WB6FLY
Brent wrote:
> Well, for some reason I just can not think of this, or I'm getting too
> old ,hehe. What is the formula for dB ( power )?
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