> >It's obvious that a 50 Ohm wattmeter, unless derived by a
>thermocouple,
> >doesn't indicate a real power if the load ( as seen through the
>line or an
> >antenna tuner ) is largely reactive, or even resistive, but away of
>the
> >nominal value.
>
Usually true in practice especially with amateur products, but it need
not be so. A sensor (or directional coupler) with high directivity can
accurately indicate the forward and reverse power flowing through it,
even if the load impedance is way off the charcteristic impedance of the
line and sensor.
Steve
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