On Mon, 4 Dec 2000 01:27:54 -0500, Tom Rauch wrote:
>Not true at all Bill. Let's look at a lossless system and infinite
>generator, since that would be the extreme.
>
>The voltage, if current goes to zero, goes to infinity. The sum of
>infinity and zero is infinity. So the forward power is infinite in the
>traditional bridge.
>
>If the lossless line has a dead short exactly 1/2 wave away, the
>current would be infinite. Voltage would be zero. The sum would be
>infinity.
>
>Anything less than this perfect case would also ALWAYS result in
>a higher reading than with a matched load assuming transmitter
>power did not go towards zero.
>
>There are absolutely NO conditions of a short or open in a system
>with any directional coupler made where the readings would drop to
>zero, or read less voltage, unless the short or open was between
>the radio and the directional coupler.
______________________________________________________
If you're talking about an open or short, I'll go along with you - but
there are lots of possible faults which are intermediate between the
extremes of open or short. For example, one half of an inverted vee
falls down, or one trap of a yagi blows.
I still stand by what I said - if one is concerned about the absolute
best protection, one should monitor voltage and current separately and
not try to sum them together and monitor the sum only. I can picture
a situation where one is running an amplifier at maximum into an SWR
of say, 1:1.2 and something goes wrong which raises the SWR to 1:1.7.
If the amplifier is already running near maximum dissipation and the
protective circuit doesn't trip, damage may occur.
I also said that for most of us, including me, this is overkill, but
someone may want that degree of protection. To each his own.
73, Bill W7TI
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