Bird 43 is a useful instrument, and I agree with your points about
directional coupler meters advantages. Sensors, diodes or thermocouples
(bolometers) have instead pros and cons.
It remains the fact that also in Bird wattmeter, if one does not subtract
the reflected power from the forward reading, in event of large SWR, the
error is much bigger than 5% of plugin fs.
With an SWR of 1:6 vswr, the reflected power is 36%. FW scale reading is
thus 36% larger than (real power to load), to which adds the instrument
error.
In case of SWR, even subtracting the reflected power to the forward, the
instrument precision is not 5% but something else, since also reflected
reading suffers the same.
When the plug in is simply reversed (the most common event) the final
precision is 10% of fs.
73,
Mauri I4JMY
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