RadioBanter - View Single Post - Current across the antenna loading coil

April 8th 06, 12:42 AM posted to rec.radio.amateur.antenna

wrote:

W8JI Wrote:
The current you measure with a clamp on meter or any other reliable
current meter that does not greatly perturb the circuit is the current
that causes radiation, it is the current that causes heating, and it is
the current we would use to calculate power.

Cecil Moore wrote:
There's absolutely no argument about that. Both forward waves and
reflected waves radiate so standing waves obviously radiate. Both
forward waves and reflected waves cause I^2*R losses. Stating such
obvious technical facts is a diversion and a waste of words.

Cecil,

Please humor all of us.

You now seem to agree the current we measure, which is the current that
causes radiation, causes heating, and that we can use to determine
phase or power levels is what Roy, I, and a dozen others have been
saying.

So what exactly is the importance of this current YOU are talking
about? Since it does not cause radiation, does not cause heat, and does
not determine phase....exactly what does it do?

73 Tom

Be careful. While we can split a current into traveling wave components,
separately calculate the resulting voltages, currents, and field
strengths, then add the results to get the total (which is identical to
the result of calculating those quantities directly from the total
current), we can't do this with power, power density, or heating. If we
have two traveling current waves which sum to zero at some point, the
total current at that point is zero and the I^2*R loss caused by that
current is zero -- regardless of how large the traveling wave currents
are. It's not the sum of the heating which would have been caused by
each traveling wave independently.

Likewise, we can calculate field strength (E or H) separately from
traveling wave components if we so desire (although I can't think of any
reason why anyone would want to), then sum the field strengths to get
the total. The result will be identical to the field strength calculated
directly from the total current as is done by NEC and EZNEC. And you can
calculate a radiated power density from the total field strength. But
you can't calculate a radiated power density from each traveling wave
component and sum them to get the total power density. Doing so violates
the requirements for superposition, and you'll get the wrong answer if
you try.

Roy Lewallen, W7EL