I have backgrounds on electrical communications, but know little about EM/RF.
I would like to install outdoor antennas for experiments (receive only; I do not hold licenses, although I do intend to get one in the near future), and I want to use 4' - 8' marine antennas for this purpose. This is mainly because I want to place multiple antennas close together (so I can play with the phase differences of the signals), and yet have them tall enough so I can get line-of-sight to transmitters.
The problem is that I am trying to operate these narrowband antennas on frequencies that they are not designed to operate on. (Mutual coupling is an another problem, but I can forget about that for now.) I am not sure how well these antennas will perform if I operate them on higher frequencies, say, in the 900MHz range. What could I expect if I do this? Are there any alternatives, if I want to place multiple antennas close together?