Dan Andersson wrote in
:

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.

And render it useless for calling the coast guard, since they are
vertically polarized (unless you hinge it to come up when deployed, but
that's one more thing to break). Basically just make sure they are more
than about 4 feet apart horizontally and that, if really close, the spare
radio is switched off the feeder unless it's needed. If they are mounted
vertically, one over the other, you don't even need to do that. But the
lower one will not be as efficient or effective as the higher one.

--
Dave Oldridge+
ICQ 1800667