Tom Donaly wrote:
However, the
term "current drop" as used by Yuri was wrong. There is no place for
it in electromagnetic theory, and if you had known enough theory to
understand that, you wouldn't have answered as you did.
I've been in Las Vegas for ten days and didn't see Yuri's posting.
All I know is there is a "current drop" from the current maximum
point to the current minimum point on a transmission line with
reflections. So exactly how did Yuri use "current drop"? If it is
through a mobile loading coil, I explain exactly how that happens
on my web page through the superposition of the forward and reflected
currents. For the typical base-loaded or center-loaded shortened
mobile antenna, If+Ir at one end of the coil is NOT equal to If+Ir
at the other end of the coil even if the two currents through the
coil are of constant magnitudes. I have explained that multiple times
here with no disagreement.
For typical standing-wave antennas with loading coils:
The forward current through a loading coil is reasonably constant.
The reflected current through a loading coil is reasonably constant.
The two above facts are obeying Kirchhoff's laws.
The total current is the sum of the forward current and the reflected
current and results in a cosine function standing wave on the antenna.
The differing phases of forward current and reflected current is what
causes the variation in the total current, i.e. the current drop.
The current drop in a standing wave antenna is similar to the current
drop in a section of transmission line with reflections. The governing
equations can be found in any EM textbook and for lossless situations
are of the form:
Itot = If*e^-yz - Ir*e^+yz
Losses to radiation or I^2*R add another couple of e^-2ad (attenuation)
terms.
--
73, Cecil
http://www.qsl.net/w5dxp
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