Initially I had mine mounted like Greg, but then the ACK ELT-04 antenna had to be put there. So I moved it to the bottom of the fuselage basically below the baggage compartment. It works fine there but at the Sonex open house we were rolling the aircraft backwards to help set up the group photo and it stuck into the ground - and busted the ceramic insulator. The Sonex guys were nice enough to make us a temporary insulator out of rubber, which has sort of become permanent because it works good. That is the one downside of this location, you have to be careful when rolling backwards and we pretty much always pick up the tailwheel to move it now.
Another good view of our antenna:
Bryan Cotton Poplar Grove, IL C77 Waiex 191 N191YX Taildragger, Aerovee, acro ailerons dual sticks with sport trainer controls Prebuilt spars and machined angle kit Year 2 flying and approaching 200 hours December 23
I have a builder made 1/4 wave stainless steel bent antenna on the belly mounted just forward of the spar tunnel. The whip was actually cut down to proper size from a 102" stainless steel CB whip that I had. Tuned to center frequency 127.000 with the length of ~23.5 inches.
Used a BNC connector inside. It works very well and being a bit further forward has prevented me from having issues with it getting bent from ground contact (you can nearly get a look at it in this video (1:58-2:12) -