dB Gain -- was RE: [K3] [Elecraft] FLx GN Adding Db gain

[David Woolley (E.L)]

Jim Brown wrote:
> Lots of questions. See some answers interspersed. 
> 
> On Tue, 11 Nov 2008 18:22:50 -0800, Dick Dievendorff wrote:
> 
>> I think I usually get that right (along with kHz), but I get confused when I
>> see dBi, dBm, seemingly dBx for all X.  I presume it's a measure of loudness
>> relative to X, so a dBi is gain relative to an isotropic radiator, and dBw
>> is what with watts?  
> 
> All dB is relative -- that is, A is x dB louder or quieter than B. 

Unfortunately, on the K3, Elecraft apparently confuse the issue by using 
a "v" suffix to indicate that the dB, although not relative to a defined 
standard, are computed using the 20 Log 10 (V1/V2) method, rather rather 
than the 10 Log 10 (P1/P2) method. (Whilst these are identical if the 
load impedance is constant, they produce different results if the 
impedance isn't constant.)
> 
>> And is a dB of voltage equivalent to a dB of power or an audio dB of
>> loudness?   

Audio dB are weighted by frequency, so the same power at different 
frequencies will not produce a 0dB difference.

> 
> Broadcasters have long been in an eternal search for loudness. If the meter 
> moves below the red there isn't enough processing, and someone is going to 
> get fired. :) 

It's more complex than that.  Classical music broadcasters need to 
respect dynamic range, whereas pop music broadcasters tend to want 
maximum loudness.  FM broadcasts tend to be companded less than AM ones. 
  In the UK, at least, TV adverts are transmitted at a higher loudness 
than most programme material.



-- 
David Woolley
"The Elecraft list is a forum for the discussion of topics related to 
Elecraft products and more general topics related ham radio"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>