Keith,
Several years ago I had a 160 meter loop up in some trees around my
property.  The average height was around 15 feet, but the antenna performed
reasonably well on top band.  Unfortunately it was less than satisfactory
on 80 meters.


Much will depend on the finguration of your property and available
supports.  The 160 loop is around 560 feet around, so you would need a
square with 140 feet on a side.  For 80 meters, you'd probably do well with
a dipole if you could get it up high enough.

Good luck
73
Chris w1gm