On Sun, 3 Dec 2000 20:34:07 -0500 "Tom Rauch" <w8ji@contesting.com>
writes:
>
>> A sample of the line voltage is balanced with a sample of the
current,
>> then the two signals are added, which cancels the reflected component,
to
>> measure "power" in the forward direction. Note that it is really the
>> line voltage, not power that is being sensed -- calibrate your meter
scale
>> accordingly! And since this is a voltage based measurement, it will
only
>> be correct at the selected line impedance.
>
>It is a voltage AND current based measurement. You said so
>yourself above, and you had it right!
Hi Tom,
The point I was trying to clarify in the "note" is that the signal from
the coupler represents the line voltage (even though it is the sum of the
sample of the line voltage and a voltage derived from the line current --
assuming a non-reactive load for the moment) and so must be squared &
divided by the line impedance to obtain a power measurement. Though at
the low levels at which these couplers are typically operated, diode
non-linearities mess with the math too, making it best to calibrate the
meter empirically.
I didn't want anyone to misconstrue that it perhaps might be the
product of the voltage and current, thus directly representing power.
73,
Marv WC6W
*
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