Richard Harrison wrote:
How much current flows into an impedance of more than 1/4-million ohms?

As you know, transmission lines transform impedances. That stub likely
has an SWR around 5000:1. Assuming a driving voltage of 250V, the
current at the 1/4-million ohm point is about 0.001 amps. However,
1/4WL away, at the short in the 1/4WL stub, the current will be
~5 amps with a voltage of ~0.05V. That's an impedance of ~0.01 ohm. The
shorted stub has transformed the impedance from 1/4-million ohms at
the mouth to ~0.01 ohm at the short. That's what transmission lines do.

The question is not, "How much current flows into an impedance of more
than 1/4-million ohms?" The question is: How much current flows 1/4WL
away from that point at the shorted end of the stub? The answer is the
sum of the forward current and reflected current. The voltage at the
shorted end of a 1/4WL stub is the difference between the forward voltage
and the reflected voltage.

The voltage at the mouth of the stub is the sum of the forward voltage
and reflected voltage. The current at the mouth of the stub is the
difference between the forward current and reflected current. In the
example above, that difference is ~0.001 amp. The forward current flowing
inside the stub is ~2.505 amps and the reflected current flowing inside
the stub is ~2.495 amps.

If you don't believe the above, simply measure the RF current at the
shorted end of the stub. Someone modeled it the other day and even
the modeling program indicated that the current was sky high at
the shorted end of a 1/4WL stub.
--
73, Cecil http://www.qsl.net/w5dxp



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