The AMSAT-SM website has an article on the dual-band omni-directional 145/435 MHz Slim Jim antenna developed by N9TAX.
Lars SM0TGU comments that the antenna works great for satellite passes below 30 degrees elevation, but signals are considerably weaker on high elevation passes.
Read the AMSAT-SM article in Google English at
Further information on the N9TAX dual-band Slim-Jim antenna is at http://n9tax.com/Slim Jim Info.html
The antenna is available via the Two Way Electronix website at