In article ,
Brian Whatcott wrote:

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! :-)

Nice thought Brian.... However what you seem to forget is that
capacative couping at RF Frequencies, is determined by three things.
1. Area of the Inside the hull Plate.
2. Distance between the two Plates.
3. Conductivity of the Sea Water Plate.

A 200 Sq Ft Screen in the cabin overhead isn't near (Orders of magnitude)
big enough to be an RF Ground for a MF/HF Antenna System, by itself.
Being located far (relative in capactive terms) from the other plate
(Salt water) means that the Rf couping into the water is what, can you
guess? Less than a few Picofarads. Now calculate the RF Impedance for
such a system at ANY, and All MF/HF Marine Frequencies that you like to
use, if you have enough computer power in your supercomputer. then come
back and explain it all to the rest of the world.


Me

Well Bruce/Me, I think you need to pull your two "selves" together!

Sifting through the humorous postings, I think your bottom line is that
HF/MF vertical antennas will not work well (sometimes I think you mean
will not work at all) unless they are (1) over sal****er with a return
path capacitively coupled to the sea (at least for nonmetallic vessels);
or (2) over land with 100 quarter-wave radials in marshland.

You have labored to persuade us that less-than-perfect marine RF ground
systems are certain to disappoint.

It will surprise you, perhaps, to learn that there are many thousands of
vertical HF and MF transmitting antennas in operation in the world today
that satisfy none of those conditions, and yet enable effective
communications activities. Some on land and some over water. These
installations are supported by rigorous theory as well as by on-the-air
performance data.

If you would like to learn more about how this is being done, often with
losses of only a few dB below ideal conditions, drop in at
rec.amateur.radio.antenna and "read the mail." You'll find some
bombastic assertions and opinions to be sure, but also many reasoned
analyses and even quantitative experiments. Hope to see you there, Bruce.

Regards,

Chuck







Bruce in Alaska wrote:
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

On Sat, 30 Jul 2005 19:58:46 GMT, Me wrote:

In article ,
Brian Whatcott wrote:

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! :-)

Nice thought Brian.... However what you seem to forget is that
capacative couping at RF Frequencies, is determined by three things.
1. Area of the Inside the hull Plate.
2. Distance between the two Plates.
3. Conductivity of the Sea Water Plate.

A 200 Sq Ft Screen in the cabin overhead isn't near (Orders of magnitude)
big enough to be an RF Ground for a MF/HF Antenna System, by itself.
Being located far (relative in capactive terms) from the other plate
(Salt water) means that the Rf couping into the water is what, can you
guess? Less than a few Picofarads. Now calculate the RF Impedance for
such a system at ANY, and All MF/HF Marine Frequencies that you like to
use, if you have enough computer power in your supercomputer. then come
back and explain it all to the rest of the world.


Me

Oh my! Anonymous poster, it was *YOUR* suggestion that an RF ground
of 200 sq ft of mesh under the (external hull) gel-coat was required
for a satisfactory RF ground at HF.

It was the original poster's suggestion of an elevated mesh that
caught your interest, not mine.

As you asked about antenna testing, I should mention that
a supercomputer is not really necessary: there is a handy dandy
gadget ( from MFJ ) which combines several RF test functions like
antenna bridge, SW ratio etc. It ran about $200 as I recall. I
satisfy myself with an LC meter these days - which gets one into the
ball park at $100.
eBay has an MFJ noise bridge at $25 currently.


Hmmm...the capacitance to ground of a few objects in my vicinity runs
about 45 pF per sq ft. Like me, standing on carpet It is just
possible a hi level ground screen of 200 sq ft might get you 200 X 45
pF = 9000 pF

At 3 MHz that would put the capacitive reactance at
1/2pi.f.C ohms = 6 ohms. Not that great. The actual value might
well be quite a bit higher than that.
But that's just me measuring with an instrument, rather than you
guessing how poor it is.
Another thing: the conductivity of sea water does not vary all that
much - it doesn't have much impact on capacitance. But there I go
again, actually measuring things!

Regards

Brian Whatcott
p.s. I have an FCC GROL+rdr. You?

On Sat, 30 Jul 2005 19:35:36 GMT, Me wrote:

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.....


Ah, well, well!
How much area does a light aircraft tube fuselage etc., subtend?

Could it possibly be, like, 200 sq feet?
And it can transmit successfully, using this as its ground plane?

You mean, like a 200 ft ground plane in a boats cabin overhead?

:-)

Brian Whatcott

On Sat, 30 Jul 2005 19:29:39 GMT, Me wrote:
/// 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.
///
Me been there, done that......for a long long time.....


Oh my, anonymous poster, you compare a frequency deviation of
2.5% at VHF (135 - 139 MHz) with a frequency change of
250kHz at (say) 3 MHz But wait: that's a 8.3% change.

And you say that the effect of a 250kHz difference at HF is much
greater than 4 MHz at VHF?

Well yes! 8.3% is much greater than 2.5%

How long did you say you have been doing this sort of thing?

:-)

Brian W

On Sat, 30 Jul 2005 18:41:54 GMT, Bruce in Alaska
wrote:


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


Bruce in alaska

Hehe...a blow hard is not silenced quite that easily!

:-)

Brian W

On Sat, 30 Jul 2005 21:45:27 GMT, chuck wrote:

Well Bruce/Me, ///
It will surprise you, perhaps, to learn that there are many thousands of
vertical HF and MF transmitting antennas in operation in the world today
that satisfy none of those conditions, and yet enable effective
communications activities. Some on land and some over water. These
installations are supported by rigorous theory as well as by on-the-air
performance data.
///
Regards,

Chuck

I see that he realises that airborne trailing wire antennas can work
well at HF with just a tube fuselage as a ground reference - miles
away from ground!

This just about completely contradicts his earlier posts about ground
references needing to be in close proximity to the ground for
successful HF work, wouldn't you say?

Brian Whatcott Altus OK

Me wrote in news:Me-
:

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



Hee hee....Don't hold back, Skip! Tell us what you REALLY think of SGC's
crapware!....(c;

REAL tuners are manually operated and say Nye-Viking on the front of them.
I own the 3KW model from the 60's. Wet noodles explode above 500
watts!...(c;

You can tell if your ground is poor on big ham transmitters. You hear
screaming when you whistle, briefly, into the metal microphone...as your
hands burn in effigy.

73 DE W4CSC

--
Larry

On Sat, 30 Jul 2005 19:41:03 GMT, Me wrote:

In article et,
"Roger Derby" wrote:


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.

Roger

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

Me

I just had a wild guess that if Roger was agreeing with anonymous
poster 'me' and me was agreeing with Roger, then Roger was probably
going to be in error too.

So I checked a Roger fact: that 4215 kHz = 75 meters = 277 ft.

Here's the scoop:
4215 kHz = 71.2 meters = 233.5 ft

Waddaya know!

:-)

Brian Whatcott

Hey, like I said, magic. Bent coat hangers also radiate. The fuselage
gives you a place to terminate the coax shield. Wiggle the connection to
the radiator until the SWR is not too bad.

Also, don't get hung up on "conductivity." Both soil and water have less
than silver, but the resistance is what counts and that's the product of
conductivity and conductor cross-section. If it floats your boat, it has a
LARGE cross-section.

Roger (changing radar detector diodes in 1955)

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

"Brian Whatcott" wrote in message
...
On Sat, 30 Jul 2005 19:35:36 GMT, Me wrote:

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.....


Ah, well, well!
How much area does a light aircraft tube fuselage etc., subtend?

Could it possibly be, like, 200 sq feet?
And it can transmit successfully, using this as its ground plane?

You mean, like a 200 ft ground plane in a boats cabin overhead?

:-)

Brian Whatcott