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.

--
Dave * N3WTK (DM04xf) * http://isi.mtwilson.edu * VE

I wanted to add that I will bring either my little homebrew QRP CW
(based on a Norcal 40), or use this as an excuse to buy an FT857.

73,

--
Dave * N3WTK (DM04xf) * http://isi.mtwilson.edu * VE

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

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.

Take a look at the www.njqrp.org/pac-12 website. I built one of these and
have been very happy with it. The wire ground radials may prove to be a
problem, but the idea might be worth considering. I've used it while camping.

....Edwin

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~ Edwin Johnson ....... ~
~ http://www.shreve.net/~elj ~
~ ~
~ "Once you have flown, you will walk the ~
~ earth with your eyes turned skyward, ~
~ for there you have been, there you long ~
~ to return." -- da Vinci ~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Dave, N3WTK wrote:
"What suggestions have you for an antenna?"

Avoid the sharks off Cocos Island.

From a boat at sea, you have a perfect earth connection available. Dunk
an electrode and use it for HF. If the boat is metal, just make a ground
connection outside to the hull. HF won`t penetrate the metal. Then use a
vertical wire as an antenna. The sea short-circuits horizontal
polarization. L-antennas are often used on boats. The horizontal portion
is just capacitive loading for the real antenna which is the vertical
portion. Loaded vertical whips are another type of common boat antenna.

Best regards, Richard Harrison, KB5WZI

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

David Snyder Hale wrote in message ...
I wanted to add that I will bring either my little homebrew QRP CW
(based on a Norcal 40), or use this as an excuse to buy an FT857.

http://www.buddipole.com/

Pricey but worth it.


73,

w3rv

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

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