NEC-LIST: NEEDS NEC81 Network Card

Gentlemen;

    Your guidance on the following will be greatly appreciated.

    I have been trying (unsuccessfully) to use the NEC81 network card
(NT) from the NEEDS package to analyze an antenna and an associated
matching network. My configuration drives the input to the network
and feeds the antenna with the output of the network. My objective is
to display the impedance seen looking into the input of the network
when the network is terminated with the antenna, i.e., to see how well
the matching network does.

    For the sake of analysis, I have used a simple dipole in free
space for the antenna and a single hypothetical 1 meter segment as the
point of entry for the network. Also for the sake of simplicity, I
have used a unity network - that is, a pass-thru having a direct
connection from input to output and no shunting impedance. What is
placed on the output of this network will be seen on the input and
vice versa. The short-circuit admittance parameters describing this
network have been taken as Y11 = Y22 = infinity and Y12 = minus
infinity.

    My NEC81 input code is shown at the end of this e-mail. My
results can be summarized as follows:

(1) The drive voltage placed on the input of the network does indeed
appear correctly as the drive for the antenna. This is shown under
the NEC81 output heading "- - - STRUCTURE EXCITATION DATA AT NETWORK
CONNECTION POINTS - - -". In addition, under the same heading is
shown the correct antenna drive point impedance and the drive power.

(2) Unfortunately, while the correct voltage appears under the above
heading as drive for the network, the impedance and power listed
appears to be that seen looking into the hypothetical 1 meter entry
segment - not the impedance and power seen looking into the network.

    I would appreciate any comments and especially those concerning
(a) Is my implementation correct? (b) Is my interpretation of the
results correct? (c) Is NEEDS NEC81 intended to display the impedance
seen looking into the hypothetical drive section and if so, why would
anyone be interested in that? (d) How can I modify the program to
display the impedance looking into the network. (I have the Fortran
source code and a means to compile but I do not have the knowlege and
patience to trace all the variables.)

Thank you for your assistance.

J.L. Smith
Ocean Springs, Mississippi
jlsmith_at_datasync.com

CE Dipole in free space
GW101,21,0.,0.,0.,97.4445,0.,0.,.00254
GW102,1,48.22225,2.0,0.,49.22225,2.0,0.,.00254
GE0
NT1021,101,11,1.E+10,0.,-1.E+10,0.,1.E+10,0.
FR0,1,0,0,1.5,0.0
EX0,102,1,00,269.,0.
GN-1
XQ
EN

NOTE:

1. My version of NEEDS NEC81 does not accept commas after the the
card identifiers nor does it accept a comma after the TAG identifier
on the NT card.
Received on Wed May 12 1999 - 19:57:43 EDT