[Elecraft] Amplifiers in general

[Jim Brown]

On Sat,12/31/2016 7:01 AM, Bill wrote:
> I have always been under the impression the doubling of output power 
> will result in a power gain of 3 db. 

Right.

> And, that 3 db gain is the least signal increase noticeable at the 
> receiving point.

Wrong.  As an audio professional, I had to learn a lot about human 
perception of sound. Here are some things I've learned, both by studying 
what others have learned and by my own observations.

1) If some sound is all by itself (that's all that you here, no other 
sounds), 1 dB is the smallest change in level that most listeners will 
hear.

2) If some sound is surrounded by other sounds -- a single instrument in 
a band or orchestra, a signal in noise, a 1 dB change can be the 
difference between hearing it and not hearing it. When I mixed live 
sound for 20-40 piece orchestras (Tony Bennett, for example), correcting 
a balance problem usually involved slightly moving the fader for the 
instrument that was too loud or not loud enough. When adjusting voice 
paging levels in an office building, 2-3dB was the difference between 
not quite loud enough to get over the air conditioner noise and being to 
loud. A change in the frequency response of a dB or two can be the 
difference between sounding "right" or not.

3) If a sound is all by itself, it takes a change in level of 6-10 dB to 
be perceived as "twice" (or "half" as loud. But that doesn't apply to a 
transmitter, because we have a volume control on our radio. :)

4) Human voice levels vary widely as we talk. Variations of 20 dB are 
common.

5) Voice frequencies in the range of 500 - 3,000 Hz are most critical 
for speech intelligibility.

In addition to running more power, we can get gain from improving  our 
antenna system. A more efficient counterpoise/radial system for a 
vertical, feedline with lower loss, a more efficient antenna tuner, and 
the biggie, an antenna that better focuses its radiation at the 
elevation, and/or in the direction, that gets to the other station. We 
can use audio compression, and we can equalize our audio to transmit 
only the parts of our voice that provides the greatest speech 
intelligibility. Compression and EQ, if done well, can yield an 
effective 13 dB of gain! All of those dB add up with the power that 
we're running. Nearly all TV and radio broadcasting makes extensive use 
of dynamics processing to make their signal as loud as possible, and the 
most skilled use careful equalization on the microphones of talkers that 
matter.

73, Jim K9YC