I have become interested in trying to develop antennas for hemispheric
coverage for circularly polarized signals. My interest in related to 137
MHz weather satellites, but not restricted to that frequency.
I have one concept for receiving NOAA satellite signals that is slightly
better than with a Quad Helix.

My reason for this post is to try to communicate with anyone with interest
in this antenna development as a hobby. That is - I'd like to be able to
exchange ideas with another amateur antenna hobbyist.

Jerry

This sounds very much like the requirement faced by GPS receivers, so
you might also try some forums dealing with that technology. To my
knowledge, patch and quadrifilar helix antennas seem to be the most
commonly used.

Roy Lewallen, W7EL

Jerry Martes wrote:
I have become interested in trying to develop antennas for hemispheric
coverage for circularly polarized signals. My interest in related to 137
MHz weather satellites, but not restricted to that frequency.
I have one concept for receiving NOAA satellite signals that is slightly
better than with a Quad Helix.

My reason for this post is to try to communicate with anyone with interest
in this antenna development as a hobby. That is - I'd like to be able to
exchange ideas with another amateur antenna hobbyist.

Jerry

Hi Roy

I have tried to locate someone in the commercial level of antenna
development to "show off" what I have uncovered with this hemispheric
coverage antenna concept. I have no interest in making money with this
concept. But, I am proud to have developed it.

It would wrong for me to say that this concept is any better than a Quad
Helix for anything except NOAA satellite imaging. Its main superiority is
its sensitivity to signals at the horizon, and thats no more than 6 dB.
A major benefit associated with this design concept is it's being non
critical to manufacturing tolerances. So, I thought it would be
interesting to guys who build their own APT antennas.

The concept is -- an array of two pairs of 1/2 wave dipoles spaced about
1/4 wave apart and tilted slightly from vertical. One pair is fed in phase
with each other. The other pair is also fed in phase with each other, but
90 degrees later than the other pair.

Jerry

"Roy Lewallen" wrote in message
...
This sounds very much like the requirement faced by GPS receivers, so you
might also try some forums dealing with that technology. To my knowledge,
patch and quadrifilar helix antennas seem to be the most commonly used.

Roy Lewallen, W7EL

Jerry Martes wrote:
I have become interested in trying to develop antennas for hemispheric
coverage for circularly polarized signals. My interest in related to 137
MHz weather satellites, but not restricted to that frequency.
I have one concept for receiving NOAA satellite signals that is
slightly better than with a Quad Helix.

My reason for this post is to try to communicate with anyone with
interest in this antenna development as a hobby. That is - I'd like to
be able to exchange ideas with another amateur antenna hobbyist.

Jerry

Interesting. Does this really maintain circular polarization throughout
the hemisphere, or does it become elliptical or linear in some directions?

Roy Lewallen, W7EL

Jerry Martes wrote:
Hi Roy

I have tried to locate someone in the commercial level of antenna
development to "show off" what I have uncovered with this hemispheric
coverage antenna concept. I have no interest in making money with this
concept. But, I am proud to have developed it.

It would wrong for me to say that this concept is any better than a Quad
Helix for anything except NOAA satellite imaging. Its main superiority is
its sensitivity to signals at the horizon, and thats no more than 6 dB.
A major benefit associated with this design concept is it's being non
critical to manufacturing tolerances. So, I thought it would be
interesting to guys who build their own APT antennas.

The concept is -- an array of two pairs of 1/2 wave dipoles spaced about
1/4 wave apart and tilted slightly from vertical. One pair is fed in phase
with each other. The other pair is also fed in phase with each other, but
90 degrees later than the other pair.

Jerry

Hi Roy

Last year I "thought up" this super simple concept while driving along the
freeway. Thats how simple it is. At that time I had no idea what the
axial ratio of the RHCP would be in the "other directions. I could see (in
my mind) that it would be excellent RHCP at the horizon, toward North,
South, East and West., in free space.
I build maybe 50 different full size models in my effort to improve the
performance. I was able to record some decent NOAA satellite pictures with
the prototypes so I had strong hopes that the CP in the rest of the
hemisphere was "OK".
Richard Clark occasionally helped my clear my thinking while I was
building prototypes.. Then one day he suggested that I try modeling the
concept with EZNEC. That EZNEC almost takes the work out of antenna
design. With the computer modeling program, I am able to demonstrate that
the free space radiation pattern shape in RHCP is Very good throughout the
hemisphere.

One thing I like about the "Double Cross" concept is that anything a guy
builds will work. The design has no tight tolerances on anything if/when
the dipoles are phased properly.

I'd be honored to know that you'd look at my EZNEC file. Tell me if
you'd consider reviewing one of the antennas that I consider quite good for
APT imaging from NOAA weather satellites.

Jerry


"Roy Lewallen" wrote in message
...
Interesting. Does this really maintain circular polarization throughout
the hemisphere, or does it become elliptical or linear in some directions?

Roy Lewallen, W7EL

Jerry Martes wrote:
Hi Roy

I have tried to locate someone in the commercial level of antenna
development to "show off" what I have uncovered with this hemispheric
coverage antenna concept. I have no interest in making money with this
concept. But, I am proud to have developed it.

It would wrong for me to say that this concept is any better than a
Quad Helix for anything except NOAA satellite imaging. Its main
superiority is its sensitivity to signals at the horizon, and thats no
more than 6 dB.
A major benefit associated with this design concept is it's being non
critical to manufacturing tolerances. So, I thought it would be
interesting to guys who build their own APT antennas.

The concept is -- an array of two pairs of 1/2 wave dipoles spaced
about 1/4 wave apart and tilted slightly from vertical. One pair is fed
in phase with each other. The other pair is also fed in phase with each
other, but 90 degrees later than the other pair.

Jerry