McGuffin wrote in news:alias-669331.23561212092008
@news.xs4all.nl:

Heard about the split-lead antenna. Any comments?
Will the stainless steel stay not absorb too much transmitting energy?
Would a well isolated long wire attached to the backstay not be
equally
good?
thanks
h



http://gamelectronicsinc.com/ssb.htm

I assume you mean this antenna. I can't imagine anyone giving him a
patent. We've have capacitive-coupled, shunt fed antennas since radios
didn't have tubes!

Here's some ham antennas that are shunt fed:
http://books.google.com/books?id=f3a...A200&lpg=PA200
&dq=shunt+fed+HF+antenna&source=web&ots=
068q5afDOP&sig=_hf2BSSU9P9HErucoiPPISocWjU&hl=en&s a=X&oi=book_result&res
num=10&ct=result#PPA195,M1

oops, this is better:

http://tinyurl.com/4g5d4n

The shunt fed match with a capacitor in series is called a "gamma
match" and is very old. It does reduce atmospheric noise as they should
be properly grounded at the bottom....making them much safer from static
discharge...st elmos fire.

The "element" in his antenna is separated from the backstay by an
insulator, creating a long sort of capacitor to couple the RF to the
backstay some distance up the backstay from its base, which may or may
not be actually grounded. Most rigging isn't grounded anywhere as that
costs boat manufacturers money and reduces profits, mostly for Brunswick
Corporation in the USA. I'm 3rd mate deck and engineering on two French
boats, one a Jeanneau 40DS and it's backstay has no ground, neither does
the backstay on the main of the Amel Sharki 41 ketch. I'm not using
insulators on either one of them. The tuner for the Jeanneau is inside
the hull to port of the steering quadrant with a plastic-coated solid
copper wire against the insulating hull to a tiny hole next to the
embedded plate the backstay is bolted to. The wire on the outside
simply goes to a clamp made to connect a ground wire to a conduit and
coated to keep the salt off it with clear spray. From the middle of the
marina in Charleston, SC, I talked to hams across Europe, South America
and as far across the Pacific as Perth, Western Australia on it. The
top of the backstay is connected to the also-ungrounded mainmast and
shrouds. It's called shunt feeding and the whole rigging radiates
fairly well.

On the Sharki, there is an insulator at the mast end of the backstay.
The triattic has two insulators, one on each end. An added Copperweld
wire connects the low end of the upper backstay, which is RF hot up to
the middle of the triattic forming a capacitor hat which pulls my
antenna current up the backstay further on the lower HF frequencies on 2
and 4 Mhz bands. The Amel's Icom AT-130 tuner is mounted outside on top
of the aft cabin roof hidden by a whitebord table/drink holder my
captain made for it in his woodshop. RF power doesn't seem to change
the taste of English Ale and Bloody Marys in our extensive research.
The enlarged antenna is easily tuned by the AT-130 on any frequency
because it's so large.

I don't see why his shunt fed "split lead" antenna shouldn't be able to
load your backstay, IF it is long enough to get enough capacitance for
the lowest frequencies where it would fail first. These little tuners
will load about anything bigger than a wet noodle. Whether it radiates
better, I doubt it. Sailboat antennas all suck, untuned longwires with
very lossy tuners in a forest of interfering other parallel metal wires
that suck off most of the signal.

Any conductive material that runs parallel to your backstay antenna
anywhere near it will suck off your signal instead of radiating it.
Case in point is the boom lift from the rear end of the boom to the top
of the mast. Ours used to be a steel cable and if you had the mast as
far out either side as possible, getting this offending wire away from
the backstay, signals went up in and out. Close hauled parallel to the
backstay and 8" from it with the boom on centerline was like
disconnecting the backstay and signals sucked! We simply replaced the
steel wire with nylon line and now it makes no difference where the boom
is. My suggestion to throw the mizzen mast overboard to improve HF
signal strength was not well received by the sailing crew, even though
the damned thing almost makes no difference in her trim and speed. They
all have visions of sailing a 4-masted schooner, the more sails the
better. They constantly play with mizzen foresails which seem to make
them happier. I never figured out what the hurry was to "get there".
They need a jet.

A 23' whip like:
http://www.boatersland.com/sha5310r.html
works quite well on a back corner of the boat, especially above 6 Mhz.
They are too short for good radiation on 2 and 4 Mhz, even with an
excellent ground system most boats don't have. Low frequency waves
don't fit well on only 23' of wire...and that's all they are, a wire
inside a fiberglass rod.

A word on "ground". "Ground" doesn't really need to be attached to the
ocean, any more than this guys split loaded antenna needs to be attached
to the backstay. RF couples quite well through paint and fiberglass,
making yet another series capacitor between the ground peg on the tuner
and the ground of the ocean. RF couples quite nicely through the hull.
I don't recommend connecting "ground" on any tuner straight to the sea
because of electrolysis in the loop between the ship's ground the tuner
is connected to and the underwater grounded stuff. I put a .01 uf RF
coupling capacitor in series with the ground system right at the tuner,
or just inside the hull if the tuner is outside. No DC can flow through
the capacitor, but RF zips right through such a low Xc and low impedance
doorknob cap. We fooled around with an isolated ground strip on the
Amel because I could get free copper flashing because the captain is in
the major commercial construction business. A 4" wide enameled copper
flashing goes fore and aft as straight as I can get it along the length
of the hull. Its aft end has a SMOOTH curve up to the ground of the
tuner. It works very well, even on 2 Mhz. Don't try to be neat and
cute with RF grounding. NO SHARP CORNERS! RF doesn't turn well.
Corners must be as large as possible with smooth wide turns. Folding it
into something that looks peachy neat may look good on a DC
multimeter....but RF thinks it's an inductor turn that blocks the RF we
want to go through the turn. Nobody looks in your bilge to bitch about
the smooth turns in your RF ground system....(c;