Geoff Schultz wrote in
:

I will be pulling my mast and am planning on adding a second VHF
antenna for a dedicated AIS receiver and eventually an AIS
transponder. However, I'll end up with both of my VHF antennas next
to one another. I suspect that this isn't a good idea. Any
suggestions as to how to handle this?

-- Geoff


The radiation pattern of the antennas is a donut out horizontal,
perpendicular to the whip.

Off the ends of the whip is a line of little to null signal.

So, if you use VERTICAL separation, with the two antennas directly
over/under one another, the coupling between them is negligible. There
will be some interference, depending on how much vertical separation you
can provide. The farther apart, the better.

I'd like to suggest putting one antenna at the top of the mast, such as a
Metz Manta 6 sticking up above the mast. Then another Metz Manta 6
hanging upside down from a shroud support about a foot from the metal
mast. It won't foul the sails in line with the shrouds and will have
"some" vertical separation away from the other VHF transceiver. If you
have a radar mount on the mast, hang a Metz Manta 6 upside down from the
bottom of it as far out from the mast as you can get it. This is also a
good place for a second VHF 1/2 wave antenna.

They will interfere with each other anywhere you put them but the signal
on the receiving antenna will be as low as you can get it and certainly
not dangerous to the receivers' front end amps. The interference comes
from signal re-radiated by all the metal rigging up there, which forms
parasitic antennas making your radiation pattern just awful and certainly
not a donut...(c;

Larry
--
While in Mexico, I didn't have to press 1 for Spanish.
While in Iran, I didn't have to press 1 for Farsi, either.
It just isn't fair.