Oscar, You can use the same groundplane, but you should reverse the antennas.
The ELT signal will be picked up be satellites, so it should be on top. The VHF comm signal is going to ground stations, so it should be below. This means that you definitely will not be able to hear anything on VHF when the ELT is triggered. Is it possible to extend the aluminum base plate with wires, foil tapes, or some other conducting material? The ground plane should have a RADIUS about 5% bigger than heighth of the driven element. That means that it should be about 54 inches in diameter. If you can get four wires or rods about 90 degrees apart that are 54 inches from tip to the opposite tip, you will greatly enhance your signals. I have used 3/32" brazing rod with great success. If you don't need the rigidity, then aircraft or house electrical wire would be fine. Jim Vance va...@claflinwildcats.com
