Re: K2 on sailboat?

[Doug Netherton]

Tom,

The big problem with antannas and a sailboat (unless it is primarily
made from wood) is all the metal in the mast and stays.  Perhaps you
could shunt feed a mast or stay like some people shunt feed a tower for
80 or 160 meters, I don't know.   If you own the ship, perhaps you could
put insulators in the stays and end feed them as dipoles of the bands
you are interested in.

And then there is the question of do you want to operate while in
motion.  A sailboat in motion needs the deck clear of "stuff" to work
all that rigging correctly.  While docked, you could haul the centre of
a dipole up the mast with a halyard and push out the dipole ends with
big fishing poles like SD20's.  We did it one Field Day from a docked
sailboat.
http://www.qsl.net/ve3mcf/fd2002/40m/Dipole40M.html

I guess it depends on your objectives and length of stay on the boat...  
There are hams that live on their boat.  Your check out their web sites
for antenna information.

73, Doug, VE3MCF

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[Brendan Minish-2]

On Sun, 2004-10-17 at 08:59 -0400, Doug Netherton wrote:
> Tom,
> The big problem with antannas and a sailboat (unless it is primarily
> made from wood) is all the metal in the mast and stays.

It's often not actually a problem, You just need to account for the
effects that they will have on the antenna system

I did the antenna design for Northabout www.northabout.com it's an
insulated backstay but the length of the insulated section was chosen
carefully to provide good low angle performance on 20 and 17m whilst
avoiding lengths that would present an impedance that would be close to
or outside the range that the (terrible!) SGC 230 coupler can match. SGC
couplers are widely used in marine setups but this does not make them
reliable or trouble free..

To work out the optimum length for the insulated backstay I modelled the
antenna (including the mast and all rigging ) in EZNEC and we managed to
get several dBi gain out of the backstay on 20m at low angles. This gain
comes from some of the rest of the rigging and the mast acting as
reflectors.

Another antenna option is to only insulate the bottom of a stay and feed
the stay and mast as a loop, this can however lead to RF hotspots


One issue with plastic and timber boats is getting a good ground. Metal
foil inside the hull can help and some folk get a metal mesh covering a
few square metres layered into the fibreglass when the boat is being
made.

If you start bonding the various bits of metal aboard to improve the
earth efficiency please be aware of any potential electrolysis problems
you may be

--
Brendan EI6IZ <[hidden email]>
--
Brendan EI6IZ <[hidden email]>

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[Stuart Rohre]

It is very standard to use the back stay guy of the main mast for antenna on
a sail boat.  It works very well, if the boat has an adequate ground plate
and bonding of the metal of the craft to radio ground.  Metal towers used
with slopers are no different from a metal mast and a slanted back stay
antenna wire.  They work lots of DX.  Most of the 20m maritime net folks use
a version of this system, and have good signals into USA from their sailing
locales.


Yes, take your K2 on a sailboat and you can use the back stay by insulating
it, and feeding it with one of the random wire tuners.  The k2 tuner may
well work fine for 20m and up depending on the length of the backstay.
72,
Stuart
K5KVH


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