On Sat, 30 Jul 2005 06:12:33 GMT, Me wrote:

In article .com,
"Skip Gundlach" wrote:

As further background, we have full rails, with the gates combined
electrically with brass straps belowdecks, attached to the arch, the
pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail,
unless you count the inner rails, plus the arch. In addition we have
the standard 4" copper strapping leading to a sintered bronze Guest
plane below the boat, and also connected to a 3x5' plate under the
workbench top. I think we have a reasonably good ground.

You will never know if you have a "reasonably good ground", unless
you get yourself an Impedance Bridge, and check it at the frequencies
that you commonly work. Anything that is more than 12" away from the
water, isn't going to add "diddley-squat" toward building a Low Impedance
Wideband RF Ground System, /// If
you got a Plastic Hull, you are NEVER going to get a Real RF Ground,
UNLESS the hull builder was smart, (they never are) and put 200+ Sq
Ft of screen under the gellcoat down by the keel. Cellulose hulls
are just as bad, and harder to retrofit that Plastic ones.
Like I said in my first reply, Autotuners were invented to allow any
"Dufus" to think he install an MF/HF Marine Radio System, and save
himself all that money he would have paid a Compitant Radioman.////
Me


Hehe...why don't you tell us what you really think, anonymous poster?

If it takes 200 sq ft of screen under a gel coat to make a good RF
ground, then folks who attempt a similar feat through a hull would
need about 0.5 / 0.05 X 200 sq ft of material - That's 2000 sq ft of
foil or metal mesh (for a 0.05 in gelcoat, and a mere 0.5 inch hull
thickness)

Now THAT would be quite a trick - a square about 100 ft by 20 ft.
Better not tell the folks who use an antenna coupled through a 1/4
inch glass shield - a coupler that can measure 1.5 inch square.
Admitted, this is often for FM radio (say 90 MHz) as opposed to
3MHz (?) on hf. Using these numbers for comparison,
90/3 X 0.5/0.25 X 2.25 sq in = 135 sq in of ground plane, hmmmm that's
1 sq foot in round numbers. Now that *does* look small to me.

I expect the truth lies somewhere between 1 sq ft and 2000 sq ft.
through a half inch hull section. There! How mealy-mouthed is THAT!
:-)

OK, let's get serious: how about locating a bronze through hull,
and connecting a copper foil externally in contact with it.
a square foot THERE, connected internally with good Litz wire might
make a serviceable ground....

Brian Whatcott Altus
p.s A hint for you: talking about "compitant radiomen" makes
prospective customers nervous! :-)

You seem to be saying that sea water (which is one heck of a lot less
conductive than copper -- I mean orders of magnitude less conductive) is
the only rf ground (return path) that works? And that the only way to
utilize it in a fiberglass hull is with capacitive coupling?

By your reasoning, radio communication from a vessel on fresh water is
impossible.

Or, as a corollary, radio communication from a vessel on the hard is
impossible because the capacitive coupling to the sea is over a distance
of more than 12".

And of course, for VHF, we all use the equivalent of copper that is not
capacitively coupled to the sea. Since we all agree that VHF works fine
that way, can you tell us at what frequency the laws of electromagnetic
radiation "jump ship" and no longer work the same as at VHF? A reference
would be most welcome. The issue here is radiation, not propagation.

Can you also provide a reference to the published and repeatable testing
of 400 sq. ft. of copper ground that didn't work any better than having
nothing at all? Radio stations thousands of miles from the sea would be
amazed to learn that their ground systems don't work better than nothing
at all.

Why not post your theory on rec.radio.amateur.antenna and see how it is
received there?

Suggest you reef those sails a tad, Me.

Chuck



Me wrote:
In article .com,
"Skip Gundlach" wrote:


As further background, we have full rails, with the gates combined
electrically with brass straps belowdecks, attached to the arch, the
pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail,
unless you count the inner rails, plus the arch. In addition we have
the standard 4" copper strapping leading to a sintered bronze Guest
plane below the boat, and also connected to a 3x5' plate under the
workbench top. I think we have a reasonably good ground.


You will never know if you have a "reasonably good ground", unless
you get yourself an Impedance Bridge, and check it at the frequencies
that you commonly work. Anything that is more than 12" away from the
water, isn't going to add "diddley-squat" toward building a Low Impedance
Wideband RF Ground System, and anyone who tells you otherwise, is just as
uneducated about MF/HF Marine Radio Antenna Systems, as you seem to be.
I have seen all kinds of Systems that looked very impresive, untill they
were evaluated with real insurmentation. 400 Sq Ft of Copper Screen in
the Cabin Overhead was proffered, as a really good RF Ground, by a well
known Boat Builder, 20 years ago. It didn't work any better than
having nothing at all, when tested, in a real radio enviorment. If
you got a Plastic Hull, you are NEVER going to get a Real RF Ground,
UNLESS the hull builder was smart, (they never are) and put 200+ Sq
Ft of screen under the gellcoat down by the keel. Cellulose hulls
are just as bad, and harder to retrofit that Plastic ones.
Like I said in my first reply, Autotuners were invented to allow any
"Dufus" to think he install an MF/HF Marine Radio System, and save
himself all that money he would have paid a Compitant Radioman.
SGC Autotuners are some of the worst of the lot, even if they did steal
the design from the real inventers. SGC couldn't even copy the design
correctly, and "Old PeeAir" couldn't design his way out of a "Wet Paper
Bag".

Me

When you talk of capacitive coupling, frequency does matter. (Xc =
1/[2*pi*F]) There's two orders of magnitude difference between HF at 1.8
MHz and VHF at 180 MHz.

"Ground" is one of those elusive concepts that get more magic/conundrum (aka
BS) than it deserves. A full dipole needs no ground. The whip or backstay
needs a ground plane so that its "virtual image" creates a full dipole.

Note that aircraft use HF communications with a half dipole antenna
(trailing wire) with no ground plane. Of course they do have an excellent
antenna height. (Don't hold the end in your fingers to test on the surface.
When your boss hits the transmit key, it hurts, for weeks.)

Antennae are magic.

Roger

http://home.earthlink.net/~derbyrm

"chuck" wrote in message
ink.net...
You seem to be saying that sea water (which is one heck of a lot less
conductive than copper -- I mean orders of magnitude less conductive) is
the only rf ground (return path) that works? And that the only way to
utilize it in a fiberglass hull is with capacitive coupling?

By your reasoning, radio communication from a vessel on fresh water is
impossible.

Or, as a corollary, radio communication from a vessel on the hard is
impossible because the capacitive coupling to the sea is over a distance
of more than 12".

And of course, for VHF, we all use the equivalent of copper that is not
capacitively coupled to the sea. Since we all agree that VHF works fine
that way, can you tell us at what frequency the laws of electromagnetic
radiation "jump ship" and no longer work the same as at VHF? A reference
would be most welcome. The issue here is radiation, not propagation.

Can you also provide a reference to the published and repeatable testing
of 400 sq. ft. of copper ground that didn't work any better than having
nothing at all? Radio stations thousands of miles from the sea would be
amazed to learn that their ground systems don't work better than nothing
at all.

Why not post your theory on rec.radio.amateur.antenna and see how it is
received there?

Suggest you reef those sails a tad, Me.

Chuck



Me wrote:
In article .com,
"Skip Gundlach" wrote:


As further background, we have full rails, with the gates combined
electrically with brass straps belowdecks, attached to the arch, the
pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail,
unless you count the inner rails, plus the arch. In addition we have
the standard 4" copper strapping leading to a sintered bronze Guest
plane below the boat, and also connected to a 3x5' plate under the
workbench top. I think we have a reasonably good ground.


You will never know if you have a "reasonably good ground", unless
you get yourself an Impedance Bridge, and check it at the frequencies
that you commonly work. Anything that is more than 12" away from the
water, isn't going to add "diddley-squat" toward building a Low Impedance
Wideband RF Ground System, and anyone who tells you otherwise, is just as
uneducated about MF/HF Marine Radio Antenna Systems, as you seem to be.
I have seen all kinds of Systems that looked very impresive, untill they
were evaluated with real insurmentation. 400 Sq Ft of Copper Screen in
the Cabin Overhead was proffered, as a really good RF Ground, by a well
known Boat Builder, 20 years ago. It didn't work any better than
having nothing at all, when tested, in a real radio enviorment. If
you got a Plastic Hull, you are NEVER going to get a Real RF Ground,
UNLESS the hull builder was smart, (they never are) and put 200+ Sq
Ft of screen under the gellcoat down by the keel. Cellulose hulls
are just as bad, and harder to retrofit that Plastic ones. Like I said
in my first reply, Autotuners were invented to allow any "Dufus" to think
he install an MF/HF Marine Radio System, and save himself all that money
he would have paid a Compitant Radioman.
SGC Autotuners are some of the worst of the lot, even if they did steal
the design from the real inventers. SGC couldn't even copy the design
correctly, and "Old PeeAir" couldn't design his way out of a "Wet Paper
Bag".

Me

Thanks for the comments, Roger.

While I don't disagree with what you have said (except that antennae are
magic), I don't believe your remarks touch on the issues here.

The typical marine VHF antenna, for example, does not depend upon the
sea for its operation. I am assuming the usual quarter-wave ground plane
vertical atop a mast. Do you believe that because VHF and HF antennas
involve different frequencies the underlying theory is different?

A backstay "vertical" antenna may or may not depend on the sea for its
return path. Me has unequivocally asserted that it always depends on the
sea and thus its ground must be coupled to the sea. (400 sq. ft. of
copper is no better than nothing at all he believes)

Conventional antenna theory suggests that a backstay "vertical" could
utilize a counterpoise or other return path element (like a horizontal
dipole half) with no coupling to the sea at all.

Me asserts this is false: that such an antenna will not work.

I attempted to present a "reductio ad absurdum" argument showing that if
Me is correct, his reasoning leads to absurd results. There is no magic
here.

I would be pleased to reconsider any of my comments if they appear
incorrect or incomprehensible.

Regards,

Chuck








Roger Derby wrote:
When you talk of capacitive coupling, frequency does matter. (Xc =
1/[2*pi*F]) There's two orders of magnitude difference between HF at 1.8
MHz and VHF at 180 MHz.

"Ground" is one of those elusive concepts that get more magic/conundrum (aka
BS) than it deserves. A full dipole needs no ground. The whip or backstay
needs a ground plane so that its "virtual image" creates a full dipole.

Note that aircraft use HF communications with a half dipole antenna
(trailing wire) with no ground plane. Of course they do have an excellent
antenna height. (Don't hold the end in your fingers to test on the surface.
When your boss hits the transmit key, it hurts, for weeks.)

Antennae are magic.

Roger

http://home.earthlink.net/~derbyrm

"chuck" wrote in message
ink.net...

You seem to be saying that sea water (which is one heck of a lot less
conductive than copper -- I mean orders of magnitude less conductive) is
the only rf ground (return path) that works? And that the only way to
utilize it in a fiberglass hull is with capacitive coupling?

By your reasoning, radio communication from a vessel on fresh water is
impossible.

Or, as a corollary, radio communication from a vessel on the hard is
impossible because the capacitive coupling to the sea is over a distance
of more than 12".

And of course, for VHF, we all use the equivalent of copper that is not
capacitively coupled to the sea. Since we all agree that VHF works fine
that way, can you tell us at what frequency the laws of electromagnetic
radiation "jump ship" and no longer work the same as at VHF? A reference
would be most welcome. The issue here is radiation, not propagation.

Can you also provide a reference to the published and repeatable testing
of 400 sq. ft. of copper ground that didn't work any better than having
nothing at all? Radio stations thousands of miles from the sea would be
amazed to learn that their ground systems don't work better than nothing
at all.

Why not post your theory on rec.radio.amateur.antenna and see how it is
received there?

Suggest you reef those sails a tad, Me.

Chuck



Me wrote:

In article .com,
"Skip Gundlach" wrote:



As further background, we have full rails, with the gates combined
electrically with brass straps belowdecks, attached to the arch, the
pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail,
unless you count the inner rails, plus the arch. In addition we have
the standard 4" copper strapping leading to a sintered bronze Guest
plane below the boat, and also connected to a 3x5' plate under the
workbench top. I think we have a reasonably good ground.


You will never know if you have a "reasonably good ground", unless
you get yourself an Impedance Bridge, and check it at the frequencies
that you commonly work. Anything that is more than 12" away from the
water, isn't going to add "diddley-squat" toward building a Low Impedance
Wideband RF Ground System, and anyone who tells you otherwise, is just as
uneducated about MF/HF Marine Radio Antenna Systems, as you seem to be.
I have seen all kinds of Systems that looked very impresive, untill they
were evaluated with real insurmentation. 400 Sq Ft of Copper Screen in
the Cabin Overhead was proffered, as a really good RF Ground, by a well
known Boat Builder, 20 years ago. It didn't work any better than
having nothing at all, when tested, in a real radio enviorment. If
you got a Plastic Hull, you are NEVER going to get a Real RF Ground,
UNLESS the hull builder was smart, (they never are) and put 200+ Sq
Ft of screen under the gellcoat down by the keel. Cellulose hulls
are just as bad, and harder to retrofit that Plastic ones. Like I said
in my first reply, Autotuners were invented to allow any "Dufus" to think
he install an MF/HF Marine Radio System, and save himself all that money
he would have paid a Compitant Radioman.
SGC Autotuners are some of the worst of the lot, even if they did steal
the design from the real inventers. SGC couldn't even copy the design
correctly, and "Old PeeAir" couldn't design his way out of a "Wet Paper
Bag".

Me

We're not discussing theory, we're discussing implementation. VHF and HF
differ significantly due to near-field considerations as well as physical
dimensions. A ground plane for a VHF whip can live on the same pole. For
HF, you'd need a MUCH bigger boat.

We once asked the lab to do a finite element analysis of a hunk of beef
being roasted. They came back later and said there wasn't enough computer
power in the world to do the job due to the various elements (water, fat,
protein, bone, etc.) By the same token, HF antenna theory is useless
because so many things on the boat are part of the "near field." One can't
ignore the rails, the other antennae, the people walking about, ...

In general, I tend to agree with "me" that the sea is the significant ground
plane if we're talking small boats (under 65').
400 sq.ft. of copper is 20' x 20' or so. The wavelength of 4215 KHz is 75
meters = 277 feet.

The magic comes in when the various elements interact. Even small dish
antenna are tested for their radiation pattern before going into production.
Theory, hah. Google antenna "near field" and you'll get sufficient theory,
mostly applicable to small dishes, to convince you.

As Arthur C. Clarke stated, "Any technology which is sufficiently advanced
(or complex) is indistinguishable from magic."

Roger

http://home.earthlink.net/~derbyrm
"chuck" wrote in message
ink.net...
Thanks for the comments, Roger.

While I don't disagree with what you have said (except that antennae are
magic), I don't believe your remarks touch on the issues here.

The typical marine VHF antenna, for example, does not depend upon the sea
for its operation. I am assuming the usual quarter-wave ground plane
vertical atop a mast. Do you believe that because VHF and HF antennas
involve different frequencies the underlying theory is different?

A backstay "vertical" antenna may or may not depend on the sea for its
return path. Me has unequivocally asserted that it always depends on the
sea and thus its ground must be coupled to the sea. (400 sq. ft. of copper
is no better than nothing at all he believes)

Conventional antenna theory suggests that a backstay "vertical" could
utilize a counterpoise or other return path element (like a horizontal
dipole half) with no coupling to the sea at all.

Me asserts this is false: that such an antenna will not work.

I attempted to present a "reductio ad absurdum" argument showing that if
Me is correct, his reasoning leads to absurd results. There is no magic
here.

I would be pleased to reconsider any of my comments if they appear
incorrect or incomprehensible.

Regards,

Chuck








Roger Derby wrote:
When you talk of capacitive coupling, frequency does matter. (Xc =
1/[2*pi*F]) There's two orders of magnitude difference between HF at 1.8
MHz and VHF at 180 MHz.

"Ground" is one of those elusive concepts that get more magic/conundrum
(aka BS) than it deserves. A full dipole needs no ground. The whip or
backstay needs a ground plane so that its "virtual image" creates a full
dipole.

Note that aircraft use HF communications with a half dipole antenna
(trailing wire) with no ground plane. Of course they do have an
excellent antenna height. (Don't hold the end in your fingers to test on
the surface. When your boss hits the transmit key, it hurts, for weeks.)

Antennae are magic.

Roger

http://home.earthlink.net/~derbyrm

"chuck" wrote in message
ink.net...

You seem to be saying that sea water (which is one heck of a lot less
conductive than copper -- I mean orders of magnitude less conductive) is
the only rf ground (return path) that works? And that the only way to
utilize it in a fiberglass hull is with capacitive coupling?

By your reasoning, radio communication from a vessel on fresh water is
impossible.

Or, as a corollary, radio communication from a vessel on the hard is
impossible because the capacitive coupling to the sea is over a distance
of more than 12".

And of course, for VHF, we all use the equivalent of copper that is not
capacitively coupled to the sea. Since we all agree that VHF works fine
that way, can you tell us at what frequency the laws of electromagnetic
radiation "jump ship" and no longer work the same as at VHF? A reference
would be most welcome. The issue here is radiation, not propagation.

Can you also provide a reference to the published and repeatable testing
of 400 sq. ft. of copper ground that didn't work any better than having
nothing at all? Radio stations thousands of miles from the sea would be
amazed to learn that their ground systems don't work better than nothing
at all.

Why not post your theory on rec.radio.amateur.antenna and see how it is
received there?

Suggest you reef those sails a tad, Me.

Chuck



Me wrote:

In article .com,
"Skip Gundlach" wrote:



As further background, we have full rails, with the gates combined
electrically with brass straps belowdecks, attached to the arch, the
pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail,
unless you count the inner rails, plus the arch. In addition we have
the standard 4" copper strapping leading to a sintered bronze Guest
plane below the boat, and also connected to a 3x5' plate under the
workbench top. I think we have a reasonably good ground.


You will never know if you have a "reasonably good ground", unless
you get yourself an Impedance Bridge, and check it at the frequencies
that you commonly work. Anything that is more than 12" away from the
water, isn't going to add "diddley-squat" toward building a Low
Impedance
Wideband RF Ground System, and anyone who tells you otherwise, is just
as
uneducated about MF/HF Marine Radio Antenna Systems, as you seem to be.
I have seen all kinds of Systems that looked very impresive, untill they
were evaluated with real insurmentation. 400 Sq Ft of Copper Screen in
the Cabin Overhead was proffered, as a really good RF Ground, by a well
known Boat Builder, 20 years ago. It didn't work any better than
having nothing at all, when tested, in a real radio enviorment. If
you got a Plastic Hull, you are NEVER going to get a Real RF Ground,
UNLESS the hull builder was smart, (they never are) and put 200+ Sq
Ft of screen under the gellcoat down by the keel. Cellulose hulls
are just as bad, and harder to retrofit that Plastic ones. Like I said
in my first reply, Autotuners were invented to allow any "Dufus" to
think he install an MF/HF Marine Radio System, and save himself all that
money he would have paid a Compitant Radioman.
SGC Autotuners are some of the worst of the lot, even if they did steal
the design from the real inventers. SGC couldn't even copy the design
correctly, and "Old PeeAir" couldn't design his way out of a "Wet Paper
Bag".

Me

In article ,
Me wrote:

In article .com,
"Skip Gundlach" wrote:

As further background, we have full rails, with the gates combined
electrically with brass straps belowdecks, attached to the arch, the
pushpit and pulpit. We have about 110 lineal feet of 1" SS tube rail,
unless you count the inner rails, plus the arch. In addition we have
the standard 4" copper strapping leading to a sintered bronze Guest
plane below the boat, and also connected to a 3x5' plate under the
workbench top. I think we have a reasonably good ground.

You will never know if you have a "reasonably good ground", unless
you get yourself an Impedance Bridge, and check it at the frequencies
that you commonly work. Anything that is more than 12" away from the
water, isn't going to add "diddley-squat" toward building a Low Impedance
Wideband RF Ground System, and anyone who tells you otherwise, is just as
uneducated about MF/HF Marine Radio Antenna Systems, as you seem to be.
I have seen all kinds of Systems that looked very impresive, untill they
were evaluated with real insurmentation. 400 Sq Ft of Copper Screen in
the Cabin Overhead was proffered, as a really good RF Ground, by a well
known Boat Builder, 20 years ago. It didn't work any better than
having nothing at all, when tested, in a real radio enviorment. If
you got a Plastic Hull, you are NEVER going to get a Real RF Ground,
UNLESS the hull builder was smart, (they never are) and put 200+ Sq
Ft of screen under the gellcoat down by the keel. Cellulose hulls
are just as bad, and harder to retrofit that Plastic ones.
Like I said in my first reply, Autotuners were invented to allow any
"Dufus" to think he install an MF/HF Marine Radio System, and save
himself all that money he would have paid a Compitant Radioman.
SGC Autotuners are some of the worst of the lot, even if they did steal
the design from the real inventers. SGC couldn't even copy the design
correctly, and "Old PeeAir" couldn't design his way out of a "Wet Paper
Bag".

Me

Geeze Louise "Me" give the guy a break...... He was just asking for
an opinion....


Bruce in alaska
--
add a 2 before @

In article . net,
chuck wrote:

You seem to be saying that sea water (which is one heck of a lot less
conductive than copper -- I mean orders of magnitude less conductive) is
the only rf ground (return path) that works? And that the only way to
utilize it in a fiberglass hull is with capacitive coupling?

By your reasoning, radio communication from a vessel on fresh water is
impossible.

Or, as a corollary, radio communication from a vessel on the hard is
impossible because the capacitive coupling to the sea is over a distance
of more than 12".

And of course, for VHF, we all use the equivalent of copper that is not
capacitively coupled to the sea. Since we all agree that VHF works fine
that way, can you tell us at what frequency the laws of electromagnetic
radiation "jump ship" and no longer work the same as at VHF? A reference
would be most welcome. The issue here is radiation, not propagation.

Can you also provide a reference to the published and repeatable testing
of 400 sq. ft. of copper ground that didn't work any better than having
nothing at all? Radio stations thousands of miles from the sea would be
amazed to learn that their ground systems don't work better than nothing
at all.

Why not post your theory on rec.radio.amateur.antenna and see how it is
received there?

Suggest you reef those sails a tad, Me.

Chuck

Well Chuck, now lets look at the subject a bit and see what the
difference is between your VHF analogy, and MF/HF RF Ground systems.

Copper vs Salt Water at VHF....Very significant difference in
conductivity, but it isn't conductivity that we are dealing with here.
At VHF the RF Ground side of the antenna is built into the antenna,
and needs only to be .5 meters long. (roughly) Also consider that at VHF
an antenna can operate over a very wide Frequency Range (155-159 Mhz)
without any major RF Impedance changes. This is NOT even close to being
true at MF/HF frequencies. Move your frequency 250Khz and your antenna
tuning is totally blown away.

Copper vs Salt Water at MF/HF.....Still some what significant in
Conductivity, but again it isn't conductivity we are talking about here.
When was the last time you saw a vessel dragging around a pile of copper
so as to have a Good RF Ground, no matter what the hull was made of?
At MF/HF Frequencies the RF Impedance of the Ground System is inversely
proportional to coupling to the Salt water, if the vessel is floating in
salt water. Obviously you have never tried to communicate using MF/HF
Frequencies in the Great Lakes and Mississippi River Systems from
plastic or wood hulled vessels. It is a bitch to design an effective RF
Ground for such vessels, as there just isn't enough there to make it
work, like in Salt Water. Also remember that RF Impedance changes with
Frequency, a rather LARGE point to be made here. When you are designing
a Marine RF Ground system it must work across one order of magnitude, or
better in frequency span, and provide a Low Impedance across the whole
span. Now tell us all just how you accomplish this feat of magic with
a plastic or cellulose hull sitting in fresh water? Like I said, it is
a bitch, and a compromise in the best situation.

The Laws of Physics aren't the problem here, it is how the Frequency
interacts with RF Ground System Impedance that determine how well things
work. No "Jump ship" about it, just simple Physics, that you apparently
don't have a good handle on.

Radio Stations in the MF Frequency Band use Marconi Antennas, and or
Phased Marconi Antennas, for Transmission. These have EXTENSIVE
RF Ground Systems, usually made up of over 100 1/4 Lambda length radial
wires buried 6 to 10" below the surrounding surface, depending on the
Radiation Pattern for that station, as designated on the License issued
by the FCC. These RF Grounds are engineered specifically for the site
and Radiation Pattern needed. The RF Ground for such Systems covers
significantly more area than 400 Sq Ft, and the addition of such a small
area of copper screen, wouldn't make any significant difference to the
Impedance of such a Ground System. What few HF Stations that are
licensed in the US these days, mostly use Balanced Antennas instead of
Marconi Antennas and the RF Ground isn't nearly as significant to their
operation as it is for Marconi Antennas. The significance is basically
limited to Takeoff Angles. Also of some significance here is that all
these situations are single frequency antennas, and therefor don't need
to be Low Impedance across a wide spread of frequencies (an order of
magnitude or better when opertional. If you had some practical knowledge
in the field, you would notice that if a wet, swampy field, or marshland
could be found, that is where these antenna systems are built. Can you
guess why?

Having been in both the Bradcast Engineering, and Marine Radio
Engineering end of things for MANY years, and having designed, installed,
and maintained both classes of systems, I have dealt with these issues
for MANY years, and the moral to the story IS, " It's the RF Ground,
Sonny, the RF Ground".

Me been there, done that......for a long long time.....

In article ,
"Roger Derby" wrote:

When you talk of capacitive coupling, frequency does matter. (Xc =
1/[2*pi*F]) There's two orders of magnitude difference between HF at 1.8
MHz and VHF at 180 MHz.

"Ground" is one of those elusive concepts that get more magic/conundrum (aka
BS) than it deserves. A full dipole needs no ground. The whip or backstay
needs a ground plane so that its "virtual image" creates a full dipole.

Note that aircraft use HF communications with a half dipole antenna
(trailing wire) with no ground plane. Of course they do have an excellent
antenna height. (Don't hold the end in your fingers to test on the surface.
When your boss hits the transmit key, it hurts, for weeks.)

Antennae are magic.

Roger

Actually the aircraft skin, if metal, or in the case of doped fabric
covered planes, the tube frames, becomes the RF Ground system for
aircraft MF/HF antenna systems. Thats why you almost NEVER see an MF/HF
Radio installed in a spruce framed, fabric coverd, aircraft, and if you
did see one it wouldn't work very well.


Me who actually has an Aircraft Endorsement on
his First Graph ticket.....

In article . net,
chuck wrote:

Thanks for the comments, Roger.

While I don't disagree with what you have said (except that antennae are
magic), I don't believe your remarks touch on the issues here.

The typical marine VHF antenna, for example, does not depend upon the
sea for its operation. I am assuming the usual quarter-wave ground plane
vertical atop a mast. Do you believe that because VHF and HF antennas
involve different frequencies the underlying theory is different?

A backstay "vertical" antenna may or may not depend on the sea for its
return path. Me has unequivocally asserted that it always depends on the
sea and thus its ground must be coupled to the sea. (400 sq. ft. of
copper is no better than nothing at all he believes)

Conventional antenna theory suggests that a backstay "vertical" could
utilize a counterpoise or other return path element (like a horizontal
dipole half) with no coupling to the sea at all.

Me asserts this is false: that such an antenna will not work.

I attempted to present a "reductio ad absurdum" argument showing that if
Me is correct, his reasoning leads to absurd results. There is no magic
here.

I would be pleased to reconsider any of my comments if they appear
incorrect or incomprehensible.

Regards,

Chuck

Best you go back to Elementary Physics, and relearn everything that you
didn't get the first time, on Antenna Theory, Frquency vs Impedance,
and Smith Charting of basic Marconi Style Antennas.....

Me

In article et,
"Roger Derby" wrote:

We're not discussing theory, we're discussing implementation. VHF and HF
differ significantly due to near-field considerations as well as physical
dimensions. A ground plane for a VHF whip can live on the same pole. For
HF, you'd need a MUCH bigger boat.

We once asked the lab to do a finite element analysis of a hunk of beef
being roasted. They came back later and said there wasn't enough computer
power in the world to do the job due to the various elements (water, fat,
protein, bone, etc.) By the same token, HF antenna theory is useless
because so many things on the boat are part of the "near field." One can't
ignore the rails, the other antennae, the people walking about, ...

In general, I tend to agree with "me" that the sea is the significant ground
plane if we're talking small boats (under 65').
400 sq.ft. of copper is 20' x 20' or so. The wavelength of 4215 KHz is 75
meters = 277 feet.

The magic comes in when the various elements interact. Even small dish
antenna are tested for their radiation pattern before going into production.
Theory, hah. Google antenna "near field" and you'll get sufficient theory,
mostly applicable to small dishes, to convince you.

As Arthur C. Clarke stated, "Any technology which is sufficiently advanced
(or complex) is indistinguishable from magic."

Roger

Roger has it right on....Not much Moss growing under hs feet.....


Me