For your perusal:
http://www.cebik.com/wire/hl.html
http://www.cebik.com/fdim/atl1.html
http://www.cebik.com/wire/horloop.html



Here is a nice horiz loop program from
http://www.smeter.net/antennas/rjeloop4.php

"This program is self-contained and ready to use. It does not require
installation."
Click this link
http://www.smeter.net/software/rjeloop4.exe
then click Open to run from the web or Save to save the program to your hard
drive.

After you have entered the initial values you can vary the frequency up or
down. Then watch how the efficiancy and loss characteristics barely vary.