>The qth here is on an 800' hilltop with 200-300' drop and horizon
in the three main directions. Any suggestions before I start planning
this next project?
This is a very complex question best answered with:
1. N6BV's Terrain Analysis (YT) available with recent ARRL Antenna
Handbooks (but it does not handle out of phase antennas).
2. NEC modeling of two stacked yagi's with BIP/BOP (both in phase
and both out of phase) as well as the individual patterns.
3. Actually, K6STI's Terrain Analysis (TA) would be the very best
since it combines 1 and 2 above, but I'm not sure Brian is still
selling it. His e-mail is firstname.lastname@example.org
My personal guess is that you would be better off with two
medium Yagi's (like 204BA's) at 40' and 90' with the ability to do
either and BIP/BOP than you would with a single monster Yagi. Given
your effective height, you have to be careful to not get only low
angles. From here in NC, there are two predominant angles to Europe
on 20 meters (1-3 degrees and 7-8 degrees) and a single antenna will
probably not cover both well.
73, Bill W4ZV