June 8th 04, 08:58 PM
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On Tue, 8 Jun 2004 13:56:06 -0500, (Richard Harrison)
wrote:
Walter, W2DU wrote:
"I`ll give you two ways to determine Vfwd."
Walter makes it too easy by using the power relationships, but that`s
the way it is. The forward (incident) wave is opposed by Ro in a
practical line. The reward (reflected) wave is also opposed by Ro (the
surge impedance) of the line.
Power from the transmitter is nearly the same as that delivered to the
load as loss is small and no significant room exists in the line to
store RF.
Power to the load is the difference between forward power and reflected
power.
The voltage at any point on a mismatched line is the sum of the forward
and reflected waves at that point but is merely a manifestatoion of SWR
and has little practical value. At a current or a voltage loop
(maximum), the forward and reflected amps or volts are in-phase. So, if
a line is opened at a loop point, the impedance looking toward the load
is a pure resistance regardless of the nature of the load (see page 37
of "Transmission Lines, Antennas, and Wave Guides" by King, Mimno, and
Wing).
Best regards, Richard Harrison, KB5WZI
Thanks, Richard, what you say is true, but problem is in determining the method
to find the forward voltage when the line is mismatched.
Walt
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