Ted wrote:

I've been working with some fishing boats and these guys want to have
redundent VHF setups - two radios, two antennas. Only one would be used
and turned on. My concern is that the unused antenna could couple as a
parasitic element and effect SWR of the operating antenna. Do I really
need to worry about it? If so haw far apart do the two antennas have to
be?


Ted,

One way is to place the aerials at a "non 1/4 or 1/8" wavelength apart from
each other but VHF is really not that bothered if you are more than a 1/4
away.

If you really want to be sure, just tilt the spare aerial 90 degrees in the
horizontal plane. That will limit the interaction even further.

I imagine the spare receiver have a 50 Ohms input impedance but only while
powered up! This means that there are no good way to tell whats at the end
of the spare aerial...

But, forget about the details and just install the aerials at a more than
but at a non-1/4 of a wavelength distance apart and all will be good
enough!


Cheers


Dan / M0DFI