[HCARC] How To Figure Db Gain In Amplfiers

[Gary and Arlene Johnson]

Thanks for the info Kerry.  Heard two guys arguing about Amps and gain and S units etc on 20 meters and as usual both had it wrong.  It's interesting that the gain in db going from 100 watts to 800 watts is so much greater than the loss in db going from 1500 watts to 750 watts.  It confuses people and these guys were totally confused.

Gary J
N5BAA
HCARC Secretary 2013
  ----- Original Message ----- 
  From: SARA SANDSTROM 
  To: Gary and Arlene Johnson 
  Cc: hcarc at mailman.qth.net 
  Sent: Tuesday, September 10, 2013 9:01 PM
  Subject: Re: [HCARC] How To Figure Db Gain In Amplfiers


  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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