K3 0n motorboat

[Frank C Richards]

I used the wrong terminology when I was speaking about antenna system
grounding on a boat. What I actually meant was a counterpoise system.
I agree that a vertical dipole works well but would be difficult to install
permanently
on a small boat. A vertical is most often used with a tuner. There are
standard mounts
and they are pretty easy to install and are sturdy and well suited for
marine use.
I also agree that all structures should be bonded to the counterpoise
system.
Some of the boat builders(Hatteras ,Bertram .etc) would put copper screen
into
the fiberglass layups of the flying bridge decks and roofs with a stud
connected
to it so that it could be tied into the system.
On commercial trawlers the antenna would be mounted on the mast about 30 or
35 ft above the water.It was fed with a wire about 25 or 30 ft long so it
was
actually a 55 or 60 ft end-fed.
With the outriggers lowered and acting as radials, the trawl doors and
cables in the
water and everything else bonded together, it is a pretty good counterpoise
system.

 73, Frank KB4VU
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[W2xj]

again, check with the wife.

Sent from my iPad

> On Jun 9, 2020, at 11:39 PM, Frank C Richards <[hidden email]> wrote:
>
> I used the wrong terminology when I was speaking about antenna system
> grounding on a boat. What I actually meant was a counterpoise system.
> I agree that a vertical dipole works well but would be difficult to install
> permanently
> on a small boat. A vertical is most often used with a tuner. There are
> standard mounts
> and they are pretty easy to install and are sturdy and well suited for
> marine use.
> I also agree that all structures should be bonded to the counterpoise
> system.
> Some of the boat builders(Hatteras ,Bertram .etc) would put copper screen
> into
> the fiberglass layups of the flying bridge decks and roofs with a stud
> connected
> to it so that it could be tied into the system.
> On commercial trawlers the antenna would be mounted on the mast about 30 or
> 35 ft above the water.It was fed with a wire about 25 or 30 ft long so it
> was
> actually a 55 or 60 ft end-fed.
> With the outriggers lowered and acting as radials, the trawl doors and
> cables in the
> water and everything else bonded together, it is a pretty good counterpoise
> system.
>
> 73, Frank KB4VU
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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[Jim Brown-10]

On 6/9/2020 8:37 PM, Frank C Richards wrote:

> I also agree that all structures should be bonded to the counterpoise
> system.
> Some of the boat builders(Hatteras ,Bertram .etc) would put copper screen
> into
> the fiberglass layups of the flying bridge decks and roofs with a stud
> connected
> to it so that it could be tied into the system.

All good advice, to the extent that it applies to the boat in question.
All the bonded stuff acts like more or less like the chassis of a
automobile or pickup (except that lots of stuff on modern vehicles
either isn't conductive, or those that are metal are often insulated
from each other by paint). :)

> On commercial trawlers the antenna would be mounted on the mast about 30 or
> 35 ft above the water.It was fed with a wire about 25 or 30 ft long so it
> was
> actually a 55 or 60 ft end-fed.

That would be a pretty good antenna too. I would not recommend an HF
antenna with an elevated feedpoint (or even an elevated current maxima),
simply because there's some funny lobing in the vertical pattern that
happens over water. The best way to feed a vertical on a boat is from
the base, low, near the water.

> With the outriggers lowered and acting as radials, the trawl doors and
> cables in the
> water and everything else bonded together, it is a pretty good counterpoise
> system.

Yes. But remember that THIS question was specifically about a boat
operating only on fresh water.

73, Jim K9YC

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[K7TV]

The original poster wants something aesthetically acceptable but performing
as well as possible within those limits, whatever they might be. He didn't
say it has to be a solution available over the counter. He doesn't say that
experimentation is unacceptable. So I suggest that he first construct a
temporary solution with a liberal dose of cut-and-try. That allows him to
vary size and location parameters that push the envelope to (the limits of)
size and xyl acceptability. Then construct a permanent version that looks
pretty.  What kind of antenna? Start with a vertical with counterpoise, and
give it as many variable parameters as possible. Say we start with the tiny
vertical dipole consisting of two hamsticks that someone already suggested.
Allow physical asymmetry as in making the lower half a shorter length
compared to the  upper, while retaining the symmetry in electrical length
(by means of different loading). Consider making the lower half horizontal.
Such L-shaped antennas work quite well (with some directivity), at least on
dry land. Consider two of the horizontal counterpoises for symmetry. Take
time to experiment and see what works best for you. Make the vertical
portion as tall as allowed by the xyl. Of course you need to be able to vary
the load inductors for both portions.  The counterpoise(s) can be hinged to
stay vertical close to the vertical portion when not in use, and floded down
like fishing rods to horizontal position for actual use. How to maintain the
electrical symmetry? Actually, you don't need to. You let the (L-shaped)
dipole become Off-Center-Fed, which gives you another parameter to play
with. The popular Buddipole design uses this to help with impedance
matching. You should of course use a common mode choke in any case to
prevent RF from flowing on the outside of the coax. As you get more off
(electrical) center, the need for choking will get more pronounced, until
you get really far off center, such that you have essentially an end-fed
antenna with just a tiny counterpoise. Such antennas don't need as much
common mode choking as do some of the other feed locations, but still need
some. As you vary the off-center-ishness, the feed impedance will vary. As
already mentioned, this can be used to help matching, but if you go far off
center you will need to add a matching device. A popular choice would be a
wideband ferrite-cored transformer. As you vary lengths and loading
inductances you can measure feed impedance with an analyzer, going for
resonance and most pleasing dimensions along with resonance. Then look at
the resistive impedance and consider whether a transformer is needed.

73,
Erik K7TV


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