Have you tried an halo or loop antenna? M2 Antenna's and Par Electronics makes
them. Homebrew plans are on the net.

The halo is a 1/2 wave dipole bent into a circle. Common designs use 1 turn,
but 3 turn halo's have been used, with more gain. Stacking 2 halo's also
provide additional gain. Weak signal operaters on VHF and UHF use them mobile
on a regular basis.

Randy ka4nma