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

On Jul 9, 9:49 am, Geoff Schultz wrote:
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

Mount them vertically, e.g. collinear. Perhaps one on the spreader.

Bob

dansk wrote in
ups.com:

On Jul 9, 9:49 am, Geoff Schultz wrote:
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

Mount them vertically, e.g. collinear. Perhaps one on the spreader.

Bob

I don't have spreaders as I have a carbon fiber mast.

-- Geoff

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.

Geoff Schultz wrote in
:

I don't have spreaders as I have a carbon fiber mast.

-- Geoff



Keep the antennas away from that mast, which acts like a big RF resistor
and absorbs, not reflects, RF signals....
The Metz Manta 6 requires no ground plane at all and will work just fine
atop that mast and at least 12" away from it further down.

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.

Ulrich G. Kliegis wrote in
:

Will the donut shape suffer from the absorption by the shrouds and
stays, or can that be neglected?

Any metal objects that are a significant portion of a wavelength will re-
radiate all the RF that passes by them, inducing RF current in them. The
Yagi beam antennas use this phenomenon to produce their directional
pattern, as do many other antenna arrays with parasitic elements.

The re-radiated RF from nearby metal objects, such as the sail rigging, has
its own radiation patterns happening at different phases than the radiating
element's output. The vector sum of all these various re-radiated patterns
adds and subtracts from the main antenna's pattern, creating an effective
pattern that looks just awful! There are huge nulls in the donut where the
various patterns cancel each other in certain directions. In other
directions, the combined pattern actually has more signal than the
original. As the boat rotates in azimuth, so does this pattern, making the
signals fade and get stronger as you turn.

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.

I use a little coiled ariel, about 6" long similar to the ones on a hand
held VHF. It is about 20 feet up the mast and picks up pretty well
everything within about 15 miles. Simply mounted on a right angled bracket
riveted to the mast.

Normal whip VHF ariel is on top of the mast. I believe a 2m (6ft) vertical
separation is suggested as a minimum

Phil


"Larry" wrote in message
...
Geoff Schultz wrote in
:

I don't have spreaders as I have a carbon fiber mast.

-- Geoff



Keep the antennas away from that mast, which acts like a big RF resistor
and absorbs, not reflects, RF signals....
The Metz Manta 6 requires no ground plane at all and will work just fine
atop that mast and at least 12" away from it further down.

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.