diptl.nec

zip contains tool for Antenna Modelling with examples

CM Dipole with coaxial feedline.
CM
CM This illustrates modeling of a coaxial cable by using a
CM combination of a transmission line model (for the inside of
CM the coax) and a wire (for the outside). 
CM The transmission line is about 1/2 physical wavelength long.
CM After you run the program, use 'Currents->Magnitude' on the
CM 'Geometry (F3)' window and use Page-up/down to magnify the
CM current. Note the current on the feedline. 
CM If you change the power setting using 'Settings' on the 
CM 'Main (F2)' window, then click on the wire resembling the
CM Coax, you can see how large the current is for a given power
CM input. At 100 watts, the current is greater than 100 mA
CM at the center of the feedline. This may or may not cause 
CM trouble with RFI if the feedline is close to a TV 
CM transmission line, phone line, etc. Note that the coax is
CM fully symmetrical with respect to the antenna. For
CM an explanation of what causes the current, see "Some
CM Aspects of the Balun Problem", by Walter Maxwell, W2DU,
CM QST, March 1983, or "Baluns: What They Do and How They Do
CM It" in the ARRL Antenna Compendium, Vol. 1.
CE

sy len=16.77
sy hgh=30
GW 1 20 0 -len hgh  0 -0.1 hgh  3.367e-3
GW 2 1  0 -0.1 hgh  0 0.1  hgh  3.367e-3
GW 3 20 0 0.1  hgh  0 len  hgh  3.367e-3
GW 4 1  0 -0.1 0.01 0 0.1  0.01 3.367e-3
GW 5 40 0 0.1  hgh  0 0.1  0.01 6.25e-3
GS 0 0 ft		' All in ft.
GE 0

sy Tlen=13.85
TL 2 1 4 1 50 Tlen
EX 6 4 1 0 1 0
GN 2 0 0 0 20 0.0303
FR 0 1 0 0 14 0
EN