As your test has shown, there is some signal available but a small antenna is not enough.
If it was my money being spent, I would choose a big UHF like a 91XG
http://www.solidsignal.com/pview.asp...u=853748001910
a big VHF like a YA1713
http://www.solidsignal.com/pview.asp...u=853748001910
and a pre-amp like a CM-7777
http://www.solidsignal.com/pview.asp...ku=02057207774
I would mount outside as high as possible and go into the project knowing that because of the '2edge' path that every signal has to travel, some channels may not work and others may be less than 100% reliable.
I don't work for SolidSignal but their web site is very good about providing specs.