[AMPS] SWR Protection

[Tom Rauch]

> An antenna or coax fault which causes the monitored voltage to rise
> and the current to fall, which would make the "apparent" power the
> same or similar if the two were summed.  This could be anything from a
> blown trap to a fallen dipole wire to an open in the coax somewhere. Lots
> of possibilities.  Monitoring the voltage and current separately would
> instantly detect such a fault, where monitoring the sum of the two might
> not.

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.


   



> As I recall, the gentleman was concerned about fault monitoring above and
> beyond the normal.  In my own rig, I don't have any fault monitoring at
> all except for grid overdrive.  But I do watch the SWR meter like a hawk
> and that's all I need.  Others may want more.
> 
> 73, Bill W7TI
> 
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> 


73, Tom W8JI
w8ji@contesting.com

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