I haven't been following this....but....
> BILLY:
> But, the series C will be dissipating the unwanted power--not reflecting
> it.
> If you want proof of that use a low voltage cap and feel for the heat.
The only possible heat source in a reactance is due to loss
resistance. In a good quality capacitor, loss is almost zero.
Small mica caps can be as low as 500 in Q, but transmitting caps
are normally far into the 1000's. Chip caps can be in the ten's of
thousands and higher.
In that case, the component is virtually lossless.
The bulk of efficiency loss in a transmitting system is due to
dissipative resistances in the energy conversion device that
converts dc to RF. That loss is a function of the time-varying
resistance of the device and the current through the device at every
instant of time integrated over a period of time.
Not all reflected power increases device dissipation. Some load
phase angles reduce device dissipation. Of course this also
reduces power from the dc source, efficiency can drop even while
power dissipation is reduced by a mismatch. In a case like this, a
class AB PA can shift into class C operation. This is the source of
destructive voltages when PA's are mistuned or under some
conditions of load faults. It is easy to produce voltages far in
excess of the normal operating voltages, because PA conduction
angle can be much shorter than 180 degrees even in PA's biased
for AB operation.
On the other hand some phase angles will cause the device to
conduct longer, and increase output device dissipation.
This is why theorems like the conjugate match theorem have to
stop short of predicting things that happen in non-linear areas of a
system, like at the source. The PA device is generally like a diode
in series with a time-varying resistance. The tank (or low-pass filter)
becomes an energy storage system, like a flyback transformer,
and dissipates very little power.
73, Tom W8JI
W8JI@contesting.com
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