NEC-LIST: Currents on TX line, with voltage source connected.

Dear Folks,

I have a small problem with the use of transmission lines in NEC2. Simply
stated, I notice that if I have connected a voltage source to the same
segment as a tx line, then current on that segment is different under
"Structure Excitation Data at Network Connection Points" from that under
"Antenna Input Parameters". Now the LPDA example given in NEC2 manual
says, and I quote:

"The latter is the current through the voltage source and includes the
current into the segment and into the transmission line."

I am not able to make sense of above statement. My problem is in
interpreting the electrical connection that NEC uses for such a case. What
I want is simply to connect a voltage source to a balanced twin wire tx
line.
I am asking this because different currents means different impedances at
that segment, and I fail to understand how impedance at a port can have 2
different values.

Kindly clarify the implicit electrical connection used in NEC.

With regards,
Nikhil Mehta
Visiting Student
Raman Research Institute
Sadashivnagar Bangalore 560 080

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