Tom says:
>You are viewing short term fractional cycle behavior and trying to
>use it to explain long term averaged current and power.
Yes. Just like Chaffee analysis does.
But the original point was that the gain goes down. My argument is that the
power output goes down, but the 'gain' is marginally affected. So what we
see is gain compression; a linear amplifier has constant gain over the full
input power envelope. If gain is affected, then running a kW amplifier at 10
watts out would see just as much percentage drop in output when the plate
volts is reduced as at a kW. In other words, that would say that gm is
highly dependent on plate volts. But look at curves for a tetrode, and it
ain't so. Even with a triode, the mu doesn't change that much for the plate
voltage changes we are talking about.
Amplifying the comment about gain being constant, look at some of the ads in
the magazines for VHF 'linear' amplifiers. One of them is for 'All
Modes:FM,SSB,CW'. Pin = 1/2 watt, Pout = 50 watts. Pin 1 watt, Pout 75
watts. Pin 4 watts, Pout = 100 watts. Now there's gain compression for you!
So my base line is that gain is mainly independent of plate voltage; gain
compression (and thus output power) isn't. An interesting point in small
amplifiers is that although 3rd order intercept is usually around 10dB above
the 1 dB gain compression point, that is not invariable. By using a lot of
feedback and too little biasing, you can get the 1dB compression point to
fall a lot further back. So another case where testing at small signals can
be totally misleading.
73
Peter G3RZP
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