"Owen Duffy" wrote in message
...
(Richard Harrison) wrote in news:23000-
:
Jim Lux wrote:
"in a linear system"
It produces no significant harmonics, so the system is linear.
That is a new / unconventional definition of 'linear'.
The term is usually used in this context to mean a linear transfer
characteristic, ie PowerOut vs PowerIn is linear.
Considering a typical valve Class C RF amplifier with a resonant load:
Conduction angle will typically be around 120°, and to achieve that, the
grid bias would be around twice the cutoff voltage.
If you attempted to pass a signal such as SSB though a Class C amplifier
that was biased to twice the cutoff value, there would be no output
signal when the peak input was less than about 50% max drive voltage, or
about 25% power, and for greater drive voltage there would be output. How
could such a transfer characteristic be argued to be linear?
Owen
Owen, 'linear transfer characteristic' isn't the only context for the use of the
word 'linear'. Even though the input circuit of a Class C amplifier is
non-linear, the output is linear due to the energy storage of the tank circuit
that isolates the input from the output, therefore, the output is linear. Proof
of this is that the output signal is a sine wave. In addition, the voltage and
current at the output terminals of the pi-network are in phase. Furthermore, the
ratio E/I = R appearing at the network output indicates that the output source
resistance R is non-dissipative, because a ratio cannot dissipate power. This
resistance R is not a resistor.
Walt