TLLC (http://www.vk1od.net/calc/tl/tllc.php) and TWLLC
(http://www.vk1od.net/calc/tl/twllc.htm) have been enhanced to calculate
two port S parameters and Y parameters for the described transmission
line section.

The parameters are independent of load. They are dependent on line type,
frequency, and length and are only calculated if no mismatch is specified
(to emphasis the independence of load). Because transmission lines are
repiprocal two port networks, only S11 and S21 are displayed, S22=S11 and
S12=S21; and likewise for the Y parameters.

An example use for the two port model is NEC NT network cards which use Y
parameters to describe the network.

NEC model of G5RV with NT cards for lossy transmission line
(http://vk1od.net/blog/wp-content/upl...03/g5rv-nt.nec) is an
example NEC model that uses two NT cards to model the open wire line
section and then coax for a G5RV at 3.6MHz. NEC will include the
transmission line losses in the “Network Loss” category under the Power
Budget heading in the NEC output report, and calculated Efficiency will
include the effects of the transmission line loss. The impedance seen by
the source in this example includes the effects of transformation by the
lossy line sections.

For convenience with NEC, the calculator output also contains an NT card
prototype with the Y parameters for the transmission line section.

Owen