hi
don't want to use my rig as antenna for my SSB transceiver
a long whip antenna is not very practical on an ocean going sailboat
(40ft)

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

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;

Larry,
Why would this antenna's radiation not be coupled to ground, as it is so
close and in parallel alignment with the grounded stay?
Steve

"Larry" wrote in message
...
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;

"Steve Lusardi" wrote in news:gaf992$2tl$01$1
@news.t-online.com:

Larry,
Why would this antenna's radiation not be coupled to ground, as it is
so
close and in parallel alignment with the grounded stay?
Steve



The grounded stay would re-radiate RF, probably out-of-phase partially
killing our signal, from induced currents caused by the transmitting
antenna. Every piece of metal on the boat will have induced currents,
especially near the antenna. They all contribute to screwing up the
total signal and radiation pattern.

Here is one wavelength of voltage on a wi

+ X
X X
X X
X X
0X X X
X X
X X
X X
- X

Make believe this is a sine wave which is impossible on my keyboard.

The length of a wave that travels at 300,000km/sec, the speed of light
depends on how fast we create the wave. 300/Mhz=meters of wavelength.

10 Mhz equals 30 meters (look on your old shortwave receiver for
wavelengths).

Now, if we fit this wave on a wire, such as a backstay wire, you can see
that 1/4 wavelength from 0 volts (your reference we call ground) is
either a very high + or - voltage at this instance. Because we are
holding one end of the wire at ground potential, the wave is forced to
stay so that one place on the wire is at zero volts (ground). The wave
continues to oscillate between + and - at the frequency the wave
oscillates at, so at the point 1/4 wavelength from the left end (ground)
of my rotten picture, the voltage swings from +HV to -HV at that
frequency.

At ground, however, the CURRENT wave caused by the transmitter's power
is at maximum (nearly across a short, a very low resistance). At
ground, the current swings from maximum + current to maximum - current.
1/4 wavelength away from this maximum current on this current sinewave
is a point that appears to stand still (we call them standing waves for
this reason.) The current waveform zero is 1/4 wavelength away from
this grounded point, exactly where the maximum voltage standing wave
occurs.

These conditions along any length of conductor repeat themselves every
1/2 wavelength no matter how long the wire is...out to the end.

At the grounded end (left end above), we have maximum CURRENT and
minimum VOLTAGE R=V/A, not exactly zero, but a very low number.

1/4 wavelength from that grounded point we have maximum voltage, but
almost no current, a very HIGH resistance AT THIS RF FREQUENCY.

If you were to plot R=V/A at all points along the wire, you'd get a
tangent function curve whos maximum is 1/4, 3/4, 1 1/4, 1 3/4, etc.
along this wire.

This is called the impedance at any point (Z) along the wire.

So, a solid piece of wire with RF applied to it has constantly changing
impedance along its length....from low to high to low to high.

As long as the wire is of infinite length, this is true. But that wire
is too long to drag under a bridge. We only need a wire long enough to
have a good place of high voltage (which is real easy to get on any
frequency) AND a wire long enough to have a good CURRENT place along it.
The current is harder to get on very short antennas that have an OPEN
END, instead of being grounded....the whip antenna on the stern, or the
insulated backstay with an insulator at the top.

When the antenna ends in an insulator (air in the whip), it's the OPEN
END that dictates how the wave fits on the wire. At the open end...it's
OPEN...high voltage..REALLY high voltage...and NO CURRENT as there is no
place for current to flow off the end of the wire (unless you're running
a few kilowatts like my ham mobile and it simply arcs into the air!) On
open ended antennas, we must fit the wave on the wire from this open
end, and work backwards towards the bottom where you hook the tuner.

A funny thing happens to either of these wires. If the wire is exactly
or nearly the right length to fit the wave onto, we call that a TUNED
antenna, and it will have a perfectly fitting standing wave on it, even
if it is only 1/4 wavelength long. This is called a RESONANT antenna.
When the wave fits onto the wire perfectly, only one wave shows up and
the antenna makes a HUGE RF radiation. No "tuner" is necessary. A 1/4
wavelength length of wire that's open on the top, insulated from ground,
displays a resistive load to our transmitter around 72 ohms against a
horizontal "earth", such as a large metal plate, the surface of the
ocean, or the 36 slightly longer than 1/4 wavelength wires radiating
away from your local AM radio station's 1/4 wavelength tower... The 1/4
wavelength vertical is the most used vertically polarized antenna on the
planet. That 23' whip is a resonant antenna around 10 Mhz, by the way.

The transmitters are designed to match the feed impedance of this
antenna, which with a sloping ground is around 52 ohms....just like the
coax cable.

Now, along comes your need to operate on 2, 4, 6, 8, 12, 16, 22 Mhz
marine bands.....NONE of which have a wave that fits just right on the
backstay.

If the wire is way off being "resonant" in length, the impedance
displayed to the transmitter becomes a complex circuit of either
resistance in series with capacitance, or a complex circuit of
resistance in series with inductance. Inductance and Capacitance STORE
energy as the wave increases, then RETURN this energy when the wave
decreases....in this case returning the power to the transmitter, not
radiating it towards that idiot you're trying to talk to. Every CBer
you meet will know that SWR is "bad". Standing Wave Ratio (SWR) is the
ratio of the wave the transmitter is sending DOWN the coax to the
antenna, in relation to the power being REFLECTED by the capacitance (if
the antenna is too short) or inductance (if the antenna is too long) of
the non-resonant random length wire....the backstay or 23' untuned whip
on your sailboat.

All is not lost! We put a box between the coax cable and the antenna
called a "tuner". Inside the box are a combination of inductors (coils)
and capacitors that a little computer capable of measuring what the
antenna is displaying can switch into the circuit in series and parallel
combinations until it finds a combination that "compensates" for the
capacitance or inductance of the antenna AT THIS FREQUENCY. You simply
press the TUNE button and the little computer takes a few seconds to
find the magic combination to RESONATE the antenna for this channel. It
stores what it finds, so when you come back to this frequency later, it
doesn't have to feel around for the match, it simply switches back to
what it used before then makes a small adjustment, if your mate is
leaning against the antenna detuning it, for instance.

What makes this grounded or ungrounded piece of wire RADIATE RF energy
is the COMBINATION of the VOLTAGE field (called E-field) from end to end
in parallel with the wire, and the CURRENT field (called M-field) AROUND
the wire perpendicular to it. BOTH these fields are required to RADIATE
RF energy. That's what we're trying to do by tuning the wire....get
both. There are many kinds of antennas that radiate all kinds of crazy
patterns of RF energy. Some are very directional, boat antennas are
omni-directional so it doesn't matter where you point the boat, the guy
can hear you.

Your wifi, your cellphone, your Bluetooth, all have antennas buried in
them. But at 800 or 1850 or 1900 or 2450 Mhz, their wavelengths are
VERY short, a few cm of a metal strip against the plastic case under
your hand. HF antennas at much lower frequencies must be longer, much
longer. Here's a proper HF transmitting antenna:
http://www.hawkins.pair.com/voanc/voanc14.jpg
It's about 400M high for reference, but we can't fit it on the boat!
It radiated to Europe for 50 years American propaganda, mostly for
Russians. The transmitter was from 250,000 to 1,000,000 watts. I've
been there when it was on the air. Your tooth fillings talk to you...
(c;

http://www.hawkins.pair.com/voanc/voanc03.jpg
250,000 watt transmitter that fed it....most impressive.

Sorry this went long....I used to teach electronics and still get
carried away....(c;

"Steve Lusardi" wrote in news:gaf992$2tl$01$1
@news.t-online.com:

Larry,
Why would this antenna's radiation not be coupled to ground, as it is
so
close and in parallel alignment with the grounded stay?
Steve



By the way, the most powerful AM radio stations in America run 50,000
watt blowtorch transmitters that USED to be HUGE and use amazing amounts
of power, converting most of it into heat for the cooling ponds in the
yard.

Today's 50,000 watt transmitters are made by Harris. Instead of huge
tubes and city-sized power supplies, they use 48 of these tiny
transistor modules:

http://www.hawkins.pair.com/wabcnow/wabcn14.jpg

Notice the US quarter dollar coin to show the size of them.
The modules are digitally switched on and off by the audio waveform fed
to a control circuit and are over 95% efficient, like the switching
power supply in your desktop computer. To put 50,000 watts of serious
RF power on the antenna, one only needs 55,000 watts....not 130,000 to
180,000 watts of the old transmitters...from the greedy power company.

The transmitter is actually cooled with muffin fans like the one on the
back of your computer. The old transmitters had huge air blowers or
distilled water cooling systems to take away the awful waste heat.

Any US stations you hear in Germany have this transmitter, now....

Amazing technology....

These white fuses are just like the ones in your radios....nothing
special.

If a module fails, the red light lights up, the control computer ignores
it until the technician reaches into the OPERATING high power
transmitter and pulls out the bad module while it all stays on the air
and replaces it. Noone in their cars will ever hear it fail.

That module in the picture has 8 transistors (the little black tabs with
one screw on the copper heat sinks. It, by itself, puts out 1,500 WATTS
of RF power.... The cooling air blows through the little holes in the
copper heat sink... They run 500,000 hours between failures!

Not very impressive unless you're standing at the base of the tower
listening to the hissing of the high RF power across the massive
insulator:
http://www.hawkins.pair.com/wcbs_wfan/cbsfan_twr14.jpg
BOTH WCBS and WFAN in New York City transmit on 660 Khz and 880 Khz
through that little piece of copper tubing coming out of the tuning
house using some trickery of inductance and capacitance I tried to give
you a glimpse of earlier:

"Steve Lusardi" wrote in news:gaf992$2tl$01$1
@news.t-online.com:

Larry,
Why would this antenna's radiation not be coupled to ground, as it is
so
close and in parallel alignment with the grounded stay?
Steve



By the way, the most powerful AM radio stations in America run 50,000
watt blowtorch transmitters that USED to be HUGE and use amazing amounts
of power, converting most of it into heat for the cooling ponds in the
yard.

Today's 50,000 watt transmitters are made by Harris. Instead of huge
tubes and city-sized power supplies, they use 48 of these tiny
transistor modules:

http://www.hawkins.pair.com/wabcnow/wabcn14.jpg

Notice the US quarter dollar coin to show the size of them.
The modules are digitally switched on and off by the audio waveform fed
to a control circuit and are over 95% efficient, like the switching
power supply in your desktop computer. To put 50,000 watts of serious
RF power on the antenna, one only needs 55,000 watts....not 130,000 to
180,000 watts of the old transmitters...from the greedy power company.

The transmitter is actually cooled with muffin fans like the one on the
back of your computer. The old transmitters had huge air blowers or
distilled water cooling systems to take away the awful waste heat.

Any US stations you hear in Germany have this transmitter, now....

Amazing technology....

These white fuses are just like the ones in your radios....nothing
special.

If a module fails, the red light lights up, the control computer ignores
it until the technician reaches into the OPERATING high power
transmitter and pulls out the bad module while it all stays on the air
and replaces it. Noone in their cars will ever hear it fail.

That module in the picture has 8 transistors (the little black tabs with
one screw on the copper heat sinks. It, by itself, puts out 1,500 WATTS
of RF power.... The cooling air blows through the little holes in the
copper heat sink... They run 500,000 hours between failures!

Not very impressive unless you're standing at the base of the tower
listening to the hissing of the high RF power across the massive
insulator:
http://www.hawkins.pair.com/wcbs_wfan/cbsfan_twr14.jpg
BOTH WCBS and WFAN in New York City transmit on 660 Khz and 880 Khz
through that little piece of copper tubing coming out of the tuning
house using some trickery of inductance and capacitance I tried to give
you a glimpse of earlier:

Hi Larry
Thank you for your thorough explanation.
My boat is made from aluminium, I forgot to add in my first post.
So just attaching the tuner to the backstay is not possible.

A 23"/7 mtr whip would be possible, but consider it as very vulnerable.
Waves, wind, boat being knocked-down (it is a sailboat afterall), etc.
Losing the antenna seems very realistic.

So basically an insulated backstay comes out as the best solution.
(I don't like the idea of cutting my stays though...)
h


In article ,
Larry wrote:

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.

Larry,
Excellent explanation, but I would like to know if I understood it
correctly. I believe you stated that ,yes, some radiation would be lost with
the slightly out of phase, grounded stay, coupled current radiation, but you
did not state how much of a performance impact this would make. As I have an
SEA 330, I have power to spare on the transmitter side, but the split lead
antenna's receive performance was not mentioned, nor any effect this
arrangement would make in its omni-directional ability. I guess the question
I need to answer, is this an affordable alternative to the insulated stay?
Could you elaborate?
Steve

"Larry" wrote in message
...
"Steve Lusardi" wrote in news:gaf992$2tl$01$1
@news.t-online.com:

Larry,
Why would this antenna's radiation not be coupled to ground, as it is
so
close and in parallel alignment with the grounded stay?
Steve



The grounded stay would re-radiate RF, probably out-of-phase partially
killing our signal, from induced currents caused by the transmitting
antenna. Every piece of metal on the boat will have induced currents,
especially near the antenna. They all contribute to screwing up the
total signal and radiation pattern.

Here is one wavelength of voltage on a wi

+ X
X X
X X
X X
0X X X
X X
X X
X X
- X

Make believe this is a sine wave which is impossible on my keyboard.

The length of a wave that travels at 300,000km/sec, the speed of light
depends on how fast we create the wave. 300/Mhz=meters of wavelength.

10 Mhz equals 30 meters (look on your old shortwave receiver for
wavelengths).

Now, if we fit this wave on a wire, such as a backstay wire, you can see
that 1/4 wavelength from 0 volts (your reference we call ground) is
either a very high + or - voltage at this instance. Because we are
holding one end of the wire at ground potential, the wave is forced to
stay so that one place on the wire is at zero volts (ground). The wave
continues to oscillate between + and - at the frequency the wave
oscillates at, so at the point 1/4 wavelength from the left end (ground)
of my rotten picture, the voltage swings from +HV to -HV at that
frequency.

At ground, however, the CURRENT wave caused by the transmitter's power
is at maximum (nearly across a short, a very low resistance). At
ground, the current swings from maximum + current to maximum - current.
1/4 wavelength away from this maximum current on this current sinewave
is a point that appears to stand still (we call them standing waves for
this reason.) The current waveform zero is 1/4 wavelength away from
this grounded point, exactly where the maximum voltage standing wave
occurs.

These conditions along any length of conductor repeat themselves every
1/2 wavelength no matter how long the wire is...out to the end.

At the grounded end (left end above), we have maximum CURRENT and
minimum VOLTAGE R=V/A, not exactly zero, but a very low number.

1/4 wavelength from that grounded point we have maximum voltage, but
almost no current, a very HIGH resistance AT THIS RF FREQUENCY.

If you were to plot R=V/A at all points along the wire, you'd get a
tangent function curve whos maximum is 1/4, 3/4, 1 1/4, 1 3/4, etc.
along this wire.

This is called the impedance at any point (Z) along the wire.

So, a solid piece of wire with RF applied to it has constantly changing
impedance along its length....from low to high to low to high.

As long as the wire is of infinite length, this is true. But that wire
is too long to drag under a bridge. We only need a wire long enough to
have a good place of high voltage (which is real easy to get on any
frequency) AND a wire long enough to have a good CURRENT place along it.
The current is harder to get on very short antennas that have an OPEN
END, instead of being grounded....the whip antenna on the stern, or the
insulated backstay with an insulator at the top.

When the antenna ends in an insulator (air in the whip), it's the OPEN
END that dictates how the wave fits on the wire. At the open end...it's
OPEN...high voltage..REALLY high voltage...and NO CURRENT as there is no
place for current to flow off the end of the wire (unless you're running
a few kilowatts like my ham mobile and it simply arcs into the air!) On
open ended antennas, we must fit the wave on the wire from this open
end, and work backwards towards the bottom where you hook the tuner.

A funny thing happens to either of these wires. If the wire is exactly
or nearly the right length to fit the wave onto, we call that a TUNED
antenna, and it will have a perfectly fitting standing wave on it, even
if it is only 1/4 wavelength long. This is called a RESONANT antenna.
When the wave fits onto the wire perfectly, only one wave shows up and
the antenna makes a HUGE RF radiation. No "tuner" is necessary. A 1/4
wavelength length of wire that's open on the top, insulated from ground,
displays a resistive load to our transmitter around 72 ohms against a
horizontal "earth", such as a large metal plate, the surface of the
ocean, or the 36 slightly longer than 1/4 wavelength wires radiating
away from your local AM radio station's 1/4 wavelength tower... The 1/4
wavelength vertical is the most used vertically polarized antenna on the
planet. That 23' whip is a resonant antenna around 10 Mhz, by the way.

The transmitters are designed to match the feed impedance of this
antenna, which with a sloping ground is around 52 ohms....just like the
coax cable.

Now, along comes your need to operate on 2, 4, 6, 8, 12, 16, 22 Mhz
marine bands.....NONE of which have a wave that fits just right on the
backstay.

If the wire is way off being "resonant" in length, the impedance
displayed to the transmitter becomes a complex circuit of either
resistance in series with capacitance, or a complex circuit of
resistance in series with inductance. Inductance and Capacitance STORE
energy as the wave increases, then RETURN this energy when the wave
decreases....in this case returning the power to the transmitter, not
radiating it towards that idiot you're trying to talk to. Every CBer
you meet will know that SWR is "bad". Standing Wave Ratio (SWR) is the
ratio of the wave the transmitter is sending DOWN the coax to the
antenna, in relation to the power being REFLECTED by the capacitance (if
the antenna is too short) or inductance (if the antenna is too long) of
the non-resonant random length wire....the backstay or 23' untuned whip
on your sailboat.

All is not lost! We put a box between the coax cable and the antenna
called a "tuner". Inside the box are a combination of inductors (coils)
and capacitors that a little computer capable of measuring what the
antenna is displaying can switch into the circuit in series and parallel
combinations until it finds a combination that "compensates" for the
capacitance or inductance of the antenna AT THIS FREQUENCY. You simply
press the TUNE button and the little computer takes a few seconds to
find the magic combination to RESONATE the antenna for this channel. It
stores what it finds, so when you come back to this frequency later, it
doesn't have to feel around for the match, it simply switches back to
what it used before then makes a small adjustment, if your mate is
leaning against the antenna detuning it, for instance.

What makes this grounded or ungrounded piece of wire RADIATE RF energy
is the COMBINATION of the VOLTAGE field (called E-field) from end to end
in parallel with the wire, and the CURRENT field (called M-field) AROUND
the wire perpendicular to it. BOTH these fields are required to RADIATE
RF energy. That's what we're trying to do by tuning the wire....get
both. There are many kinds of antennas that radiate all kinds of crazy
patterns of RF energy. Some are very directional, boat antennas are
omni-directional so it doesn't matter where you point the boat, the guy
can hear you.

Your wifi, your cellphone, your Bluetooth, all have antennas buried in
them. But at 800 or 1850 or 1900 or 2450 Mhz, their wavelengths are
VERY short, a few cm of a metal strip against the plastic case under
your hand. HF antennas at much lower frequencies must be longer, much
longer. Here's a proper HF transmitting antenna:
http://www.hawkins.pair.com/voanc/voanc14.jpg
It's about 400M high for reference, but we can't fit it on the boat!
It radiated to Europe for 50 years American propaganda, mostly for
Russians. The transmitter was from 250,000 to 1,000,000 watts. I've
been there when it was on the air. Your tooth fillings talk to you...
(c;

http://www.hawkins.pair.com/voanc/voanc03.jpg
250,000 watt transmitter that fed it....most impressive.

Sorry this went long....I used to teach electronics and still get
carried away....(c;

"Steve Lusardi" wrote in
:

Larry,
Excellent explanation, but I would like to know if I understood it
correctly. I believe you stated that ,yes, some radiation would be
lost with the slightly out of phase, grounded stay, coupled current
radiation, but you did not state how much of a performance impact this
would make. As I have an SEA 330, I have power to spare on the
transmitter side, but the split lead antenna's receive performance was
not mentioned, nor any effect this arrangement would make in its
omni-directional ability. I guess the question I need to answer, is
this an affordable alternative to the insulated stay? Could you
elaborate? Steve



Oh, it probably works just fine. Shunt fed antennas have worked great
for years. The problem I see in it is more related to how are we going
to keep seawater out of the insulating material between his feed and the
stay to keep the tuning stable and to keep the wet device from arcing on
some frequencies where it's at a high impedance point.

The only real way to tell how well it works is to just order it and
install it TEMPORARILY WITHOUT THE HOLES and try it out on your
backstay. If it works, install it. If not, send it back and get a
refund.

Are you SURE your backstay is grounded at the BOTTOM? That would be
very unusual in a production boat.

I'd say before you send him all this money, let's hook the RF output of
the SEA autotuner directly to the bottom of the backstay and any kind of
ground right there at the dock. Just run a jumper cable from the tuner
ground post to the engine block as directly as you can to test it. If
the bottom of the backstay is grounded it simply won't find a tuning,
especially on the lower bands. just sit the grounded tuner under the
backstay on the seating, anyplace it won't fall overboard is fine, but
as close to the backstay as you can temporarily located it. Keep the
wire from the tuner's high voltage output to the backstay as short as
possible. Listen to the receiver AFTER pushing the TUNE button and
letting the autotuner find a tuniing solution as tuning also affects
reception. If it will tune and seems to receive well, call someone at
some distance, not in your area, that you've prearranged to have
listening on the phone, maybe a couple of hundred km away. Connect the
cellphone to them so you can listen to your own signal at a
distance....above 6 Mhz in daytime, below 6 Mhz at night.

If it works, just install it! Problem solved!

If you can't find a way to get a ground to the temporary installation,
that's easy, too. Drop an anchor chain over the side and let it lay on
the bottom under the boat. Boy does THAT make a great ground! I use a
trailing wire about 30 meters long behind the boat under sail at sea.
It's just a plastic covered #16 piece of hookup wire the end of which
has been dipped in sealer so the water can't get up into it and rot the
wire. I did have a can lid on the end of it making a little sea anchor
to hold it out behind the boat, but SOMETHING BIG fell in love with that
and SWALLOWED it and half my ground wire! He must have needed iron in
his diet...(c;

McGuffin wrote in news:alias-F69096.09082513092008
@news.xs4all.nl:

Hi Larry
Thank you for your thorough explanation.
My boat is made from aluminium, I forgot to add in my first post.
So just attaching the tuner to the backstay is not possible.

A 23"/7 mtr whip would be possible, but consider it as very
vulnerable.
Waves, wind, boat being knocked-down (it is a sailboat afterall), etc.
Losing the antenna seems very realistic.

So basically an insulated backstay comes out as the best solution.
(I don't like the idea of cutting my stays though...)
h


Wow....I'd kill for an aluminum hull seawater ground....very nice!
Plastic boats suck for HF radio comms.

Let's play a trick on it before we cut the backstay all up for
insulators....

Your backstay is so well grounded at its aft end to the aluminum ground
monster, I'd recommend trying a SHUNT (parallel) feed to the backstay.


Deck Backstay Mast
(GROUND) 1/3 2/3
__________________________________________________ ______________________
|
_______ |
| | |
| TUNER |_______________|
|_______|^tuner output
|
GROUND

What we're going to do is to hang a small wire on insulators UNDER the
backstay at a distance of 30-40cm up along the backstay about 1/3rd the
length of the backstay. At 1/3 up the backstay, the wire is then
connected to the backstay. The distance from the wire to the backstay
doesn't really matter as long as it's as far away from it as you can
stand to look at.

1/3 the way up the backstay is NOT RF ground, it's some complex
impedance on any frequency. If this distance isn't far enough up the
backstay, the tuner won't be able to tune it on the lowest frequency
band you use. If this happens, make the wire longer and hook it higher
up the backstay, say 1/2 the way up. The tuner has a certain range of
impedances it can tune up....we've got to put it up far enough so the
tuner can tune it on the lowest band. Upper bands are easy to tune this
far up the backstay. Don't forget the silly sail or boom lift has to
miss the feed wire hanging down from the backstay, so that is just about
the limit how far we can put the feed wire from the backstay. Any kind
of plastic that doesn't snap easily makes a good insulator to hang this
wire from the backstay. Small diameter PVC works great. If the boom is
supported by wire rope, change it to nylon or some other line that's not
conductive. The boom lift wire rope is way too close to the backstay
when the sail is close hauled, eating your signal.

Experiment with the actual feed point to find a point that will tune on
all the channels you use.



If you get good signals fed this way, you now have what is called a
shunt-fed, Delta Loop. The Delta greek symbol, is a triangle which
consists of the backstay, down the mast and across the deck
ground...Delta loops radiate great if you can load them. Loading the
mast also loads the forestay, shrouds and all. Some power will be lost
to the wiring inside the mast backing up down those wires. You may find
wind instruments go crazy if the RF screws up the signal from the mast.
It doesn't bother ours on the Jeanneau that I can see. There's an
indicator light over the hatch to the forward cabin we installed so we
can see the masthead light is on. It glows with RF energy if the light
is off...(c;

Because it costs almost nothing to try shunt feeding that nicely
grounded backstay on your aluminum hull, you have almost nothing to lose
except a little time. Put a crockadile clamp on the backstay end of the
wire so you can move it around and find a good spot before installing it
permanently....

http://www.vias.org/radioanteng/rae_02_03_04.html
we've been shunt feeding towers like this since the 1920's.
http://www.qsl.net/w9rb/webdoc9.htm
http://www.fybush.com/sites/2007/site-070223.html