[Boatanchors] decibels (was Microphone Output)

[W2HX]

Just a minor correction:
dBm = power relative to 1 mW dissipated (this is impedance independent, not 600 ohm). 


 
73 Eugene W2HX
 

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Friday, January 11, 2013 11:40 AM
To: boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] decibels (was Microphone Output)

"dB" is the unit of measure of a relative logarithmic ratio, usually involving power or amplitude.
It needs a suffix to define a point of reference to which the reading is relative.

A few examples of these units are:
dBm = power relative to 1 mW dissipated in 600 ohms.
dBW = power relative to 1 W regardless of load impedance.
dBi =  gain of an antenna relative to an isotropic radiator.
dBd = gain of an antenna relative to a dipole in free space.
dBV =  voltage relative to 1 volt, regardless of impedance.

A chart of the ratios and more info than you want is at:
http://en.wikipedia.org/wiki/Decibel
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