I've used a single delta loop on 80 meters, with the apex at 70 feet.
I think this would scale well to a height of 45 feet on 40 meters.
I fed it at a lower corner for vertical polarization. This meant it
had great low-angle radiation, but wasn't so hot for short-haul
stuff. Depending on what other antennas you have for 40 FD, you
might want to consider feeding it in the middle of the bottom
leg, which would give it horizontal polarization, and make
it a real cloud-warmer.
The feedpoint impedance is about 100 ohms. I matched it with
a quarter-wave section of 75 ohm coax to give a nice flat, broad
Look for the Hewlett-Packard Andover Radio Club W1HJS 2A EMA!!
-Tony, K1KP, firstname.lastname@example.org