Full size verticals are hard to do on small power boats. And elevated
grounds are also hard. Water grounds are usually the most practical, but
fresh water is not great. I counsel inverted Vs as they are ground
independent. On power boats that too is a tough trick, but it can be
done, depending on size of the boat. A 40 meter dipole can be made by
bending the ends and can be fed with coax through a 4:1 current balun if
the run to the radio is not too great. It will require a fiberglass mast
bracketed to the fly bridge. There are several suppliers of good, strong
push up masts available; I wouldn't go more than about 25 feet which
should put the feed about 31 or so feet over the water,m close to a 1/4
wave on 40. This arrangement will allow all band operation above 40 with
a K3 as the tuner is just plain magic.
73,
Barry
K3NDM
------ Original Message ------
From: "Robert Sands" <[email protected]>
To: "Frank C Richards" <[email protected]>
Cc: "Elecraft Discussion List" <[email protected]>
Sent: 6/9/2020 3:22:27 PM
Subject: Re: [Elecraft] K3 on motorboat.
Verticals require more attention to ground but the goal should be to
increase the antenna current, thus increasing radiated signal. ground into
water seems like a waste but has DC grounding value. I use hung vertical
dipoles (20 and 15) with no need for ground and they work amazingly well. I
have tried letting wire or zinc ribbon strips drop into saltwater to
ground verticals and there is no value I can detect over something simpler,
like tying to existing structures or running a above water wire
counterpoise. Vertical dipoles require no Rf ground and propagate at low
angle and high efficiency. Far effects over water are what counts, more
than grounding, except in verticals to get higher antenna current.
K7VO
On Tue, Jun 9, 2020 at 7:38 AM Frank C Richards <[email protected]> wrote:
Having been in the marine electronics business I was able to successfully
install many HF radios on boats from large steel commercial fishing boats
to a small 28 ft fiberglass fishing boat and sailboats.
Anything metal , engine, fuel tanks,rudder posts,thru hulls, morse control
cables,intercoolers outside of the hull,rub rail sections jumpered together
to form one continuous loop. Dynaplates help but will not work well as the
only source of ground. I once saw a carbon brush riding thru spring tension
on a prop shaft, tying the prop to ground.
It can be tricky as sometimes you get ground loops and you must be aware
of currents that can cause electrolysis.
For the antenna we primarily used a 23 ft whip, sometimes on large vessels
a longwire.
This was before synthesized radios and autouners. My favorite radio was
the
Drake TRM which had a built in manual tuner and a 50 ohm output if you
wanted
to use a trapped vertical.
On commercial fishing boats you had to leave the dock so that the
outriggers
could be lowered and trawl doors put in the water as this changed the
tuning
quite a bit from being at the dock. Interestingly enough I think the
toughest
time I had tuning was on an 85 ft steel shrimp boat even with all that
metal.
.
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