In article ,
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?

These must be very small fishing boats, as ALL vessels over 65 Ft MUST
have two Vhf receivers operational while navigating. Marine ch16, and
marine ch13. this is required by The Bridge to Bridge Radiotelephone
Act.
It really isn't a big deal as long as the two antennas have some
seperation either vertical or horozontal. I have installed multiple
MORAD 156HD antennas on a Masthead Tree, using 24inch Standoffs,
and not had any problems with simulataious operations as long as the
radio's frequencies were seperated by 50Khz or more. Of course I
was working with good commercial type Vhf's like Modar55/75 or
SEA156's, and not the RayJeff consumer crap that one would usually find
on noncommercial vessels.

Bruce in alaska
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add a 2 before @