[Elecraft] Re: K2 on sailboat?

[Brendan EI6IZ]

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 <ei6iz at newsguy.com>
-- 
Brendan EI6IZ <ei6iz at oceanfree.net>