[HCARC] How To Figure Db Gain In Amplfiers

[SARA SANDSTROM]

Gary, 

The formula is 20 log base 10(power output / Power input).  It has to be power and the same units, ie, kW / kW,  mW / mW, etc.  For 500 W with 100 W input the answer is 7 dB while for 600 W with the same  100 W input it is 8 dB.  No it isn't linear but approximately so over limited ranges.  These are of course approximate numbers but at the cost of being politically incorrect (as if I care!) any one who thinks hams can measure to less than a dB should be wouff-hunged!  Two traps are the formula doesn't work for voltage or current and be careful you are actually measuring power at the appropriate impedance levels.  Most ham instruments don't compensate for impedance differences and are more or less inaccurate. 

Have fun, 

Kerry  

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