"Goofball_star_dot_etal" wrote in message
news
On Wed, 2 Apr 2008 13:10:05 -0600, "Bob Crantz"
wrote:


"Wilbur Hubbard" wrote in message
ctanews.com...
I have personal experience with respect to this topic. Putting a wi-fi
antenna at the masthead is the WRONG thing to do. You don't want it high
up. You want it low down. It gets better reception low. The signals seem
to be stronger low. Mount a good amplified antenna at deck level for the
best reception. No need to worry about long lengths of co-ax at all.

Here's a good antenna that works well and is priced reasonably.
http://www.radiolabs.com/products/wi...ne-antenna.php

Wilbur Hubbard


If your antenna is vertically polarized you could see a 3 dB increase in
signal if it placed over a conducting ground plane such as salt water.

6dB. Principle of superposition. No power splitting required for the
image. No change in antenna radiation impedance if the distance from
antenna to ground plane is large in terms of wavelengths,
as is likely to be the case in this situation.



It's 3 dB in power and it's the Principle of Images that is used to remove
the ground plane and locate a virtual mirror image of the antenna. The
Principle of Superposition is used after the Principle of Images to
calculate the field. One would tend to say it's 6 dB in voltage but that is
misleading as the input impedance varies between the real and image and it
is power (actually energy) that is conserved. You're right about the spacing
being important.

Glory!

On Thu, 3 Apr 2008 19:00:47 -0400, "Bob Crantz"
wrote:


"Goofball_star_dot_etal" wrote in message
news
On Wed, 2 Apr 2008 13:10:05 -0600, "Bob Crantz"
wrote:


"Wilbur Hubbard" wrote in message
. octanews.com...
I have personal experience with respect to this topic. Putting a wi-fi
antenna at the masthead is the WRONG thing to do. You don't want it high
up. You want it low down. It gets better reception low. The signals seem
to be stronger low. Mount a good amplified antenna at deck level for the
best reception. No need to worry about long lengths of co-ax at all.

Here's a good antenna that works well and is priced reasonably.
http://www.radiolabs.com/products/wi...ne-antenna.php

Wilbur Hubbard


If your antenna is vertically polarized you could see a 3 dB increase in
signal if it placed over a conducting ground plane such as salt water.

6dB. Principle of superposition. No power splitting required for the
image. No change in antenna radiation impedance if the distance from
antenna to ground plane is large in terms of wavelengths,
as is likely to be the case in this situation.



It's 3 dB in power and it's the Principle of Images that is used to remove
the ground plane and locate a virtual mirror image of the antenna. The
Principle of Superposition is used after the Principle of Images to
calculate the field. One would tend to say it's 6 dB in voltage but that is
misleading as the input impedance varies between the real and image and it
is power (actually energy) that is conserved. You're right about the spacing
being important.

Glory!


It is not just a question of squeezing the energy from a sphere into a
hemisphere. If the antenna and its image are separated by a number of
wavelengths nulls occur in the polar plot, so that you cannot simply
claim that a gain of more than 3dB violates the Conservation of
Energy. Principle of Superposition rules. Amen!

"Goofball_star_dot_etal" wrote in message
...

It is not just a question of squeezing the energy from a sphere into a
hemisphere. If the antenna and its image are separated by a number of
wavelengths nulls occur in the polar plot, so that you cannot simply
claim that a gain of more than 3dB violates the Conservation of
Energy. Principle of Superposition rules. Amen!

Amen!

Alright, you got me. Is that 6 dBi? If so, then I agree. Otherwise I don't
see how. Do you have a reference, example or link showing this 6 dB(dipole)
of gain for two end to end antenna separated by multiple wavelengths.

The principle of superposition states the response of a linear system is the
sum of the elements of the system. If each element is a dipole and both
dipoles are in free space, the output can never be greater than the sum of
the two dipoles acting independently.

Maybe I don't understand what you're saying but I'm definitely missing
something here. Thanks in advance for the help and insight.

Bless you!

BC

On Fri, 4 Apr 2008 09:57:55 -0600, "Bob Crantz"
wrote:


"Goofball_star_dot_etal" wrote in message
.. .

It is not just a question of squeezing the energy from a sphere into a
hemisphere. If the antenna and its image are separated by a number of
wavelengths nulls occur in the polar plot, so that you cannot simply
claim that a gain of more than 3dB violates the Conservation of
Energy. Principle of Superposition rules. Amen!

Amen!

Alright, you got me. Is that 6 dBi?

No, 'regular' common or garden dB.

f so, then I agree. Otherwise I don't
see how. Do you have a reference, example or link showing this 6 dB(dipole)
of gain for two end to end antenna separated by multiple wavelengths.

Does this help?
http://books.google.co.uk/books?id=o...hbV18#PPA91,M1

(Foundations of Antenna Theory and Techniques By Vincent F. Fusco.
page 91 )
" ....this leads to a 6dB power gain."


If one transmitter gives 1mV into a receiver the addition of a second
identical transmiter at the same distance and in phase, will give 2mV.
This is a 4 x increase in power, 6dB. You have doubled the total tx
power (3dB) so you have an antenna gain of 3dB. In the case of an
image in a 'ground plane mirror', there is no extra tx power and still
the same 6dB gain. The missing 3dB that came from the second
transmitter comes from the power that would have gone into space,
below the ground plane.

"Goofball_star_dot_etal" wrote in message
...

Alright, you got me. Is that 6 dBi?

No, 'regular' common or garden dB.

dB is a relative measurement. Is it relative to isotropic or dipole?


f so, then I agree. Otherwise I don't
see how. Do you have a reference, example or link showing this 6
dB(dipole)
of gain for two end to end antenna separated by multiple wavelengths.

Does this help?
http://books.google.co.uk/books?id=o...hbV18#PPA91,M1

(Foundations of Antenna Theory and Techniques By Vincent F. Fusco.
page 91 )
" ....this leads to a 6dB power gain."


If one transmitter gives 1mV into a receiver the addition of a second
identical transmiter at the same distance and in phase, will give 2mV.
This is a 4 x increase in power, 6dB.

Let's say one transmitter is 1 watt. The second transmitter is 1 watt, both
total 2 watts. The receiving antenna then sees a 4x increase in power by
doubling the transmit power, by the law of superposition. Got it! So the
Friis equation must be wrong:

http://en.wikipedia.org/wiki/Friis_t...ssion_equation

If the path, frequency etc are unchanged the Friis equation shows that
doubling the transmit power only doubles the receive power.

You have doubled the total tx
power (3dB) so you have an antenna gain of 3dB.

So, if the transmit power was quadrupled the receive power would go up by a
factor of 16 and the antenna gain becomes 12 dB. I never realized antenna
gain was determined by signal strength.

In the case of an
image in a 'ground plane mirror', there is no extra tx power and still
the same 6dB gain. The missing 3dB that came from the second
transmitter comes from the power that would have gone into space,
below the ground plane.

Your principles are correct but the numbers are wrong, unless you can state
3 dB relative to what?

On Fri, 4 Apr 2008 20:01:30 -0600, "Bob Crantz"
wrote:


"Goofball_star_dot_etal" wrote in message
.. .

Alright, you got me. Is that 6 dBi?

No, 'regular' common or garden dB.

dB is a relative measurement. Is it relative to isotropic or dipole?

Transmission over a ground plane compared to free space. It is
irrelevant whether the antenna is isotropic or dipole or A. N. Other,
provided there is symmetry about the plane parallel to the ground.



f so, then I agree. Otherwise I don't
see how. Do you have a reference, example or link showing this 6
dB(dipole)
of gain for two end to end antenna separated by multiple wavelengths.

Does this help?
http://books.google.co.uk/books?id=o...hbV18#PPA91,M1

(Foundations of Antenna Theory and Techniques By Vincent F. Fusco.
page 91 )
" ....this leads to a 6dB power gain."


If one transmitter gives 1mV into a receiver the addition of a second
identical transmiter at the same distance and in phase, will give 2mV.
This is a 4 x increase in power, 6dB.

Let's say one transmitter is 1 watt. The second transmitter is 1 watt, both
total 2 watts. The receiving antenna then sees a 4x increase in power by
doubling the transmit power, by the law of superposition.

Spooky!

Got it! So the
Friis equation must be wrong:

http://en.wikipedia.org/wiki/Friis_t...ssion_equation

The Friis equation does not apply to two well separated transmitters
transmitting so the (coherent) signals arrive in phase or a single
transmitter and antenna and its image.
It would apply if they were transmitting uncorrelated noise (random
relative phase.
It is the same as the difference between combining light from two
light bubs or two lasers.

Your links pecifically states:

"The antennas (tx, rx) are in unobstructed free space, with no
multipath"


If the path, frequency etc are unchanged the Friis equation shows that
doubling the transmit power only doubles the receive power.

You have doubled the total tx
power (3dB) so you have an antenna gain of 3dB.

6dB (rx) -3dB (tx) = 3dB (antenna gain)


So, if the transmit power was quadrupled the receive power would go up by a
factor of 16 and the antenna gain becomes 12 dB. I never realized antenna
gain was determined by signal strength.


Never mind...

In the case of an
image in a 'ground plane mirror', there is no extra tx power and still
the same 6dB gain. The missing 3dB that came from the second
transmitter comes from the power that would have gone into space,
below the ground plane.

Your principles are correct but the numbers are wrong, unless you can state
3 dB relative to what?

In article ,
Goofball_star_dot_etal wrote:

On Thu, 3 Apr 2008 19:00:47 -0400, "Bob Crantz"
wrote:


"Goofball_star_dot_etal" wrote in message
news
On Wed, 2 Apr 2008 13:10:05 -0600, "Bob Crantz"
wrote:


"Wilbur Hubbard" wrote in message
. octanews.com...
I have personal experience with respect to this topic. Putting a wi-fi
antenna at the masthead is the WRONG thing to do. You don't want it high
up. You want it low down. It gets better reception low. The signals seem
to be stronger low. Mount a good amplified antenna at deck level for the
best reception. No need to worry about long lengths of co-ax at all.

Here's a good antenna that works well and is priced reasonably.
http://www.radiolabs.com/products/wi...ne-antenna.php

Wilbur Hubbard


If your antenna is vertically polarized you could see a 3 dB increase in
signal if it placed over a conducting ground plane such as salt water.

6dB. Principle of superposition. No power splitting required for the
image. No change in antenna radiation impedance if the distance from
antenna to ground plane is large in terms of wavelengths,
as is likely to be the case in this situation.



It's 3 dB in power and it's the Principle of Images that is used to remove
the ground plane and locate a virtual mirror image of the antenna. The
Principle of Superposition is used after the Principle of Images to
calculate the field. One would tend to say it's 6 dB in voltage but that is
misleading as the input impedance varies between the real and image and it
is power (actually energy) that is conserved. You're right about the spacing
being important.

Glory!


It is not just a question of squeezing the energy from a sphere into a
hemisphere. If the antenna and its image are separated by a number of
wavelengths nulls occur in the polar plot, so that you cannot simply
claim that a gain of more than 3dB violates the Conservation of
Energy. Principle of Superposition rules. Amen!

It also really doesn't apply to the Original Question at hand, in that
there is a Frequency Component , inherent in the Superposition Rule,
and at 2.4 Ghz your Antenna would need to be a lot closer to the
Conducting Groundplane than Wilbur's Sailboat Handrail, for this to
have any effect.......

On Fri, 04 Apr 2008 19:17:00 GMT, You wrote:

In article ,
Goofball_star_dot_etal wrote:

On Thu, 3 Apr 2008 19:00:47 -0400, "Bob Crantz"
wrote:


"Goofball_star_dot_etal" wrote in message
news On Wed, 2 Apr 2008 13:10:05 -0600, "Bob Crantz"
wrote:


"Wilbur Hubbard" wrote in message
. octanews.com...
I have personal experience with respect to this topic. Putting a wi-fi
antenna at the masthead is the WRONG thing to do. You don't want it high
up. You want it low down. It gets better reception low. The signals seem
to be stronger low. Mount a good amplified antenna at deck level for the
best reception. No need to worry about long lengths of co-ax at all.

Here's a good antenna that works well and is priced reasonably.
http://www.radiolabs.com/products/wi...ne-antenna.php

Wilbur Hubbard


If your antenna is vertically polarized you could see a 3 dB increase in
signal if it placed over a conducting ground plane such as salt water.

6dB. Principle of superposition. No power splitting required for the
image. No change in antenna radiation impedance if the distance from
antenna to ground plane is large in terms of wavelengths,
as is likely to be the case in this situation.



It's 3 dB in power and it's the Principle of Images that is used to remove
the ground plane and locate a virtual mirror image of the antenna. The
Principle of Superposition is used after the Principle of Images to
calculate the field. One would tend to say it's 6 dB in voltage but that is
misleading as the input impedance varies between the real and image and it
is power (actually energy) that is conserved. You're right about the spacing
being important.

Glory!


It is not just a question of squeezing the energy from a sphere into a
hemisphere. If the antenna and its image are separated by a number of
wavelengths nulls occur in the polar plot, so that you cannot simply
claim that a gain of more than 3dB violates the Conservation of
Energy. Principle of Superposition rules. Amen!

It also really doesn't apply to the Original Question at hand, in that
there is a Frequency Component , inherent in the Superposition Rule,

It only means you can add things up, in this case vectors, provided
there is no interaction eg. impedance change. It breaks down "closer"
because impedance changes.

and at 2.4 Ghz your Antenna would need to be a lot closer to the
Conducting Groundplane than Wilbur's Sailboat Handrail, for this to
have any effect.......

See above.

More to the point, the sea is very rough in terms of wavelength @ 2.4
GHz (in Wales, at least, Boyo) and not a mirror. One thing at a
time.:-)

"Goofball_star_dot_etal" wrote in message
...

It only means you can add things up, in this case vectors, provided
there is no interaction eg. impedance change. It breaks down "closer"
because impedance changes.

You can add vectors even if the impedance changes.

1. Solve the field for all space with just the source.
2. Replace reradiators with equivalent sources based upon the incident field
from (1).
3. Using superposition, sum all the fields from (1) and (2) for the total
field.



and at 2.4 Ghz your Antenna would need to be a lot closer to the
Conducting Groundplane than Wilbur's Sailboat Handrail, for this to
have any effect.......

The additional signal in Wilbur's antenna comes from reflections from the
water.



See above.

More to the point, the sea is very rough in terms of wavelength @ 2.4
GHz (in Wales, at least, Boyo) and not a mirror. One thing at a
time.:-)


Yes, the rougher it gets the more reflections you see, just like a ship's
radar. The reflections are in Fresnel zone 1 which add to the signal
strength. The biggest time variations one would see in signal strength would
be due to a slow, rolling sea surface.