Cecil Moore wrote:
Roy Lewallen wrote:
Why does this seem so complicated?

The SWR bridge circuitry may not correctly display the
actual SWR. Please see my latest response to Tarmo.

The SWR bridge samples the current and voltage and
performs a phasor addition and subtraction to get
voltages proportional to the forward and reflected
powers. If there is a high voltage caused by reactive
components, it will be close to 90 degrees away from
the current. But phasor adding these two values gives
something slightly greater in magnitude than the high
reactive voltage. That high voltage gets rectified and
displayed as the forward power when it is not actually
the forward power but reactive power flowing from one
reactance to another.

Even in this unusual situation, the behavior of the meter is completely
predictable, including the incorrect power indication.

Remember that the meter doesn't actually measure power - it is only
*calibrated* to *indicate* power. When placed in a situation where its
calibration is not valid, then of course it won't indicate power
correctly. But even its wrong indication can be predicted if you know
the detailed values to plug into a circuit model.

There's really no mystery about it.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek