Antenna modeling for "listening only" is probably overkill but try the EZNEC

For a beginner, without having to bother about segments- and
tag-numbers and counts, you could try 4nec2 freeware program.
In this there is a drag- and draw style sub-program included which you
could use to 'draw' your antenne instead of specifying separate wire,
excitation, loading and/or ground records.

However, see for yourself.

Arie.