On Wed, 17 Nov 2004 04:35:36 +0000 (UTC), David Snyder Hale
wrote:

hi,

I am taking a trip on a dive boat to Cocos Island off of Costa Rica.
I'm thinking about trying to bring an HF rig. What suggestions have
you for an antenna? It would have to fit into a reasonably "standard"
suitcase, or go as carry-on luggage, since packing space is limited.

dunno how big your boat is, but possibly a "tape-measure" dipole:

http://www.gotenna.com/

bob
k5qwg

Bob, K5QWG wrote:
"dunno know how big your boat is, but possibly a "tape-measure" dipole:"

A Go-Tenna is collapsible for easy packing, but twice as long as an
equivalent monopole, used against the sea, a near perfect ground.

A Go-Tenna can be deployed as a vertical and so could be effective at
sea but requires twice the altitude of an equivalent monopole.

Horizontal deployment requires an elevation of a couple of wavelengths
at sea to be very effective. That`s usually excessive.

Recall that the ground wave is vertically polarized. There is no
horizontally polarized wave propagation over the sea.

Terman says on page 808 of his 1955 edition:
"Examination of these vector diagrams show that with s perfect reflectoe
the horizontal components of the electric field will exactly cancel each
other at the surface of the perfect reflector. In contrast the vertical
components of the electric field of the incident and reflected waves do
not cancel, but rather add at the reflector surface with small values of
Psi 2 (the vertical takeoff angle from the surface)."

Best regards, Richard Harrison, KB5WZI

On Wed, 17 Nov 2004 11:02:46 -0600, (Richard
Harrison) wrote:

Bob, K5QWG wrote:
"dunno know how big your boat is, but possibly a "tape-measure" dipole:"

A Go-Tenna is collapsible for easy packing, but twice as long as an
equivalent monopole, used against the sea, a near perfect ground.

A Go-Tenna can be deployed as a vertical and so could be effective at
sea but requires twice the altitude of an equivalent monopole.

Horizontal deployment requires an elevation of a couple of wavelengths
at sea to be very effective. That`s usually excessive.

Recall that the ground wave is vertically polarized. There is no
horizontally polarized wave propagation over the sea.

Terman says on page 808 of his 1955 edition:
"Examination of these vector diagrams show that with s perfect reflectoe
the horizontal components of the electric field will exactly cancel each
other at the surface of the perfect reflector. In contrast the vertical
components of the electric field of the incident and reflected waves do
not cancel, but rather add at the reflector surface with small values of
Psi 2 (the vertical takeoff angle from the surface)."

Best regards, Richard Harrison, KB5WZI


Are you saying that my low (less than 1/2 wavelength high) horizontal
antenna will be next to useless if I live on the sea shore? And that
same antenna will perform much better if I live inland where soil
conditions are poor?

73
Gary K4FMX

Or that only vertically polarized signals can be intercepted by ships at
sea?

Chuck


Gary Schafer wrote:
On Wed, 17 Nov 2004 11:02:46 -0600, (Richard
Harrison) wrote:


Bob, K5QWG wrote:
"dunno know how big your boat is, but possibly a "tape-measure" dipole:"

A Go-Tenna is collapsible for easy packing, but twice as long as an
equivalent monopole, used against the sea, a near perfect ground.

A Go-Tenna can be deployed as a vertical and so could be effective at
sea but requires twice the altitude of an equivalent monopole.

Horizontal deployment requires an elevation of a couple of wavelengths
at sea to be very effective. That`s usually excessive.

Recall that the ground wave is vertically polarized. There is no
horizontally polarized wave propagation over the sea.

Terman says on page 808 of his 1955 edition:
"Examination of these vector diagrams show that with s perfect reflectoe
the horizontal components of the electric field will exactly cancel each
other at the surface of the perfect reflector. In contrast the vertical
components of the electric field of the incident and reflected waves do
not cancel, but rather add at the reflector surface with small values of
Psi 2 (the vertical takeoff angle from the surface)."

Best regards, Richard Harrison, KB5WZI



Are you saying that my low (less than 1/2 wavelength high) horizontal
antenna will be next to useless if I live on the sea shore? And that
same antenna will perform much better if I live inland where soil
conditions are poor?

73
Gary K4FMX

Chuck wrote:
"Or that only vertically polarized signals can be intercepted by ships
at sea?"

I served on a navy ship in WW-2. Our antenna was a low-L. It could
intercept either polarity but responded only to line of sight and
high-angle signals. This was a deliberate design. The Navy did not want
our emissions QRM-ing the world. Our range was limited to about 500
miles. We could contact our shore destinations at about 2 days travel
from them (our ship was slow).

Best regards, Richard Harrison, KB5WZI

A local here used a 20M Hamstick in a canoe -- worked Japan from Arizona

Hamsticks at URL:
http://www.hamstick.com/

--
The Anon Keyboard
I doubt, therefore I might be

Gary, K4FMX wrote:
"Are you saying that my low (less than 1/2 wavelength high) horizontal
antenna will be next to useless if I live on the sea shore?"

No. Your antenna will do whatever it does. I said that sea water
reflects so well that the reflected ray from the sea is almost as strong
as the incident ray. At low angles they cancel when horizontally
polarized, being equal and of opposite polarity, and this eliminates
low-angle radiation. This is demonstrated in Figs. 13 & 14 on page 3-12
of the 19th edition of the "ARRL Antenna Book".

Low horizontal wires tend to send most energy straight up. This can
provide near vertical incidence contacts.

For distance, when the reflecting surface is good (sea water) and the
antenna is low, the antenna had better be placed vertically. Results are
shown in Fig 16 on page 3-13 of the same book.

Best regards, Richard Harrison, KB5WZI

On Thu, 18 Nov 2004 08:49:44 -0600, (Richard
Harrison) wrote:

Gary, K4FMX wrote:
"Are you saying that my low (less than 1/2 wavelength high) horizontal
antenna will be next to useless if I live on the sea shore?"

No. Your antenna will do whatever it does. I said that sea water
reflects so well that the reflected ray from the sea is almost as strong
as the incident ray. At low angles they cancel when horizontally
polarized, being equal and of opposite polarity, and this eliminates
low-angle radiation. This is demonstrated in Figs. 13 & 14 on page 3-12
of the 19th edition of the "ARRL Antenna Book".

The description for the radiation patterns say they are over flat
ground. Would the patterns be similar over water?

bob
k5qwg


Low horizontal wires tend to send most energy straight up. This can
provide near vertical incidence contacts.

For distance, when the reflecting surface is good (sea water) and the
antenna is low, the antenna had better be placed vertically. Results are
shown in Fig 16 on page 3-13 of the same book.

Best regards, Richard Harrison, KB5WZI

Bob, K5QWG wrote:
"The description for the radiation patterns say they are over the
ground. Would the patterns be similar over water?"

The legend says:
"The solid-line curves are the flat, perfect-earth (read sea water)
patterns, and the shaded curves represent the effects of average flat
earth---."

Best regards, Richard Harrison, KB5WZI

Hello Richard,

I think Gary and I were taking issue with your statement:

"Recall that the ground wave is vertically polarized. There is no
horizontally polarized wave propagation over the sea."

While the first sentence is correct, the second would be a bit of
surprise if it were true. Indeed, your experience on the naval vessel
utilized horizontal propagation over the sea. But it is not correct to
equate horizontal polarization with low-angle polarization.

I think I understand what you meant to say.

73,

Chuck

Richard Harrison wrote:
Gary, K4FMX wrote:
"Are you saying that my low (less than 1/2 wavelength high) horizontal
antenna will be next to useless if I live on the sea shore?"

No. Your antenna will do whatever it does. I said that sea water
reflects so well that the reflected ray from the sea is almost as strong
as the incident ray. At low angles they cancel when horizontally
polarized, being equal and of opposite polarity, and this eliminates
low-angle radiation. This is demonstrated in Figs. 13 & 14 on page 3-12
of the 19th edition of the "ARRL Antenna Book".

Low horizontal wires tend to send most energy straight up. This can
provide near vertical incidence contacts.

For distance, when the reflecting surface is good (sea water) and the
antenna is low, the antenna had better be placed vertically. Results are
shown in Fig 16 on page 3-13 of the same book.

Best regards, Richard Harrison, KB5WZI