"JosephKK" wrote in message
...
On Mon, 16 Feb 2009 18:49:47 GMT, "Jerry"
wrote:


"JosephKK" wrote in message
. ..
On Tue, 10 Feb 2009 18:12:26 -0000, "christofire"
wrote:


"Jerry" wrote in message
...

snip

Chris

Interesting article, it describes the Lindenblat array as a quartet of
coaxial horns. Not the same as a quartet of dipoles at all.


Hi Joseph

I sent an E-mail to the address shown as yours in this group. I use
EZNEC and have lots of files on various sizes and shapes of the DCA and
other OmniAzimuth and Hemispheric coverage antennas. I'd be happy to
share
them with you if you E-mail me directly.
I figure it will benefit me to see the facts and data that shows where I
am mistaken about how the DCA better than the other hemispheric coverage
antennas for LEO use. It is likely that I have overlooked something.
maybe the DCA can be improved.

Jerry KD6JDJ

Jerry KD6JDJ

I can retrieve the email. Thanks for the notice.

I have done a bit of gedanken after the slant range issue was raised.


A


B



o H
ooo
ooooo

Let the group of "o" represent a polar view of earth,
"A" represent satellite at azimuth (highest point in the sky),
"B" represent satellite between azimuth and horizon,
"Z" represent satellite very near the horizon,
nominal orbital height 1000 miles above mean surface,
and mean radius of earth of 4000 miles.
Then range to the satellite at A is about 1000 miles, at B may be
about 3000 miles and at H would be about 5000 miles. The arithmetic
for relative sensitivity versus elevation angle can even be solved
analytically, though 4 evenly spaced angles on either side of azimuth
would be quite sufficient to plot the most even EIRP curves.
Your DCA is notably more hemispherical than that. Can you tinker it
up to get about 16 dB more at the horizon than at the azimuth?

Hi Joseph

I am not familiar with all the satellite orbits. It seems that most of
the Polar Orbiting Satellites are about 500 miles above the Earth. If the
Earth radius can be considered to be 4,000 miles, the distance to the
satellite at the horizon is about 2,000 miles. That means that, the path
los from the satellite to the ground station varies by about 12 dB as it
passes overhead.
One of the objectives of the DCA design project was to produce a pattern
with about 12 dB less sensitivity toward zenith. I attempted to achieve
that pattern shape by tilting the dipoles to minimize overhead sensitivity.
Serindipity offered me a side benefit when it made me aware that tilting the
dipoles in this array effects the dipole input impedance. The input
impedance of the dipoles in a DCA with 45 degree tilt (90 degree cross) is
about 72 ohms. The dipole input impedance in a DCA with 30 degree tilt is
very near 50 ohms. Kinda lucky!!

Jerry KD6JDJ

"Jerry" wrote in message
...

"JosephKK" wrote in message
...
On Mon, 16 Feb 2009 18:49:47 GMT, "Jerry"
wrote:


"JosephKK" wrote in message
...
On Tue, 10 Feb 2009 18:12:26 -0000, "christofire"
wrote:


"Jerry" wrote in message
...

snip

Chris

Interesting article, it describes the Lindenblat array as a quartet of
coaxial horns. Not the same as a quartet of dipoles at all.


Hi Joseph

I sent an E-mail to the address shown as yours in this group. I use
EZNEC and have lots of files on various sizes and shapes of the DCA and
other OmniAzimuth and Hemispheric coverage antennas. I'd be happy to
share
them with you if you E-mail me directly.
I figure it will benefit me to see the facts and data that shows where
I
am mistaken about how the DCA better than the other hemispheric coverage
antennas for LEO use. It is likely that I have overlooked something.
maybe the DCA can be improved.

Jerry KD6JDJ

Jerry KD6JDJ

I can retrieve the email. Thanks for the notice.

I have done a bit of gedanken after the slant range issue was raised.


A


B



o H
ooo
ooooo

Let the group of "o" represent a polar view of earth,
"A" represent satellite at azimuth (highest point in the sky),
"B" represent satellite between azimuth and horizon,
"Z" represent satellite very near the horizon,
nominal orbital height 1000 miles above mean surface,
and mean radius of earth of 4000 miles.
Then range to the satellite at A is about 1000 miles, at B may be
about 3000 miles and at H would be about 5000 miles. The arithmetic
for relative sensitivity versus elevation angle can even be solved
analytically, though 4 evenly spaced angles on either side of azimuth
would be quite sufficient to plot the most even EIRP curves.
Your DCA is notably more hemispherical than that. Can you tinker it
up to get about 16 dB more at the horizon than at the azimuth?

Hi Joseph

I am not familiar with all the satellite orbits. It seems that most of
the Polar Orbiting Satellites are about 500 miles above the Earth. If the
Earth radius can be considered to be 4,000 miles, the distance to the
satellite at the horizon is about 2,000 miles. That means that, the path
los from the satellite to the ground station varies by about 12 dB as it
passes overhead.
One of the objectives of the DCA design project was to produce a pattern
with about 12 dB less sensitivity toward zenith. I attempted to achieve
that pattern shape by tilting the dipoles to minimize overhead
sensitivity. Serindipity offered me a side benefit when it made me aware
that tilting the dipoles in this array effects the dipole input impedance.
The input impedance of the dipoles in a DCA with 45 degree tilt (90 degree
cross) is about 72 ohms. The dipole input impedance in a DCA with 30
degree tilt is very near 50 ohms. Kinda lucky!!

Jerry KD6JDJ


.... but, dare I ask, what does that do to the axial ratio? Indeed, what
kind of axial ratio is being sought in this application? ... 3 dB or more?

Chris

On Feb 16, 10:03*am, JosephKK wrote:
On Tue, 10 Feb 2009 18:12:26 -0000, "christofire"



wrote:

"Jerry" wrote in message
...

"christofire" wrote in message
.. .
"Jerry" wrote in message
. ..

"Harry H" wrote in message
...

*The Lindenblad has an overhead null that you might find anoying for
some high elevation passes of LEOs.
*Are you open to trying to build a DCA (which is an antenna that I
developed)? * I make the claim that there is no other hemispheric
coverage antenna design that performs better than a DCA. * But, I sure
am open to being corrected.
*The Feb 2008 QST contains an article on the DCA antenna design
concept.
*It is my claim that a DCA is extreemely forgiving of construction
errors and uses 4 wire dipoles and 50 ohm coax with 5 RFI type
ferrites as "baluns'.

* * * * * * * * * * * *Jerry * KD6JDJ
Given the fact I don't subscribe to QST, domicile Australia, would you
have a copy of the article?

HH

*Hi HH

*It would be my pleasure to disclose any/all the information I have
relating to the DCA antenna design concept. * It is simple. *It is two
pairs of crossed dipoles. * Each pair is spaced 1/4 wave apart and fed
in phase. One pair is physically mounted 90 degrees from the other pair.
All four dipoles are tilted 30 degtrees from vertical. * One pair is fed
90 degrees later than the other pair.
*The concept is so simple and straightfoeward that it is probable that
the concept has been developed before I thought of it. * But, I have
been unable to find anything published related to this simple "Double
Cross Antenna"
*I told my *Internet buddy*, Patrik Tast, in Finland about the concept
and he found it to be exactly what he needed for reception of NOAA
weather satellite signals. * Patrik publishes alot of what I send him
related to the antenna. *Patrik shows a section of his web page to
describe the DCA to anyone interested. * You can find the QST article in
the section Patrik identifies as ANTENNAS on the first page of his site
http://www.poes-weather.com/index.php.

*If you have any questions about the DCA concept you are free to E-mail
me, anytime. * Or, if you have any facts or data to show where I am
wrong about how well this antenna performs, *or know of something that
performs better, please set me straight.

* * * * * * *Jerry * *KD6JDJ

... but surely this is the same as a Lindenblad array? *The tilt of the
dipoles was always a parameter in the Lindenblad, so I wonder how your
DCA differs from what N. E. Lindenblad described in the April 1941
edition of 'Communications'.

Chris

*Hi Chris

*Several, well educated, antenna experts insist that the DCA is actually a
Lindenblad. * If you thought the DCA is a Lindenblad, you are not alone.
*The DCA is not a Lindenblad. * The array of four dipoles in a Lindenblad
are fed to produce an overhead null. * The four dipoles in a DCA are fed
to produce no overhead null. * The DCA is a hemispheric coverage CP
antenna. The Lindenblad is not.
*Let me know if you have reason to consider the DCA to be the same as a
Lindenblad. * I knew nothing about Lindenblad until after recognizing the
DCA concept.

* * * * * * * * * * * Jerry m * *KD6JDJ

* * * * * * * * * * *Jerry

Perhaps it's a rather fine distinction to say an antenna that has the same
physical form as the Lindenblad array is something different because the
elements are driven differently. *The original version that he patented
didn't have rod elements at all (see, for example,
http://www.coe.montana.edu/ee/rwolff...ry_UWB_antenna...)
but it was the configuration of four slanted dipoles around a central pole
that appears to have borne his name since 1941. *Henry Jasik's 'Antenna
Engineering Handbook' (now by John L. Volakis, Richard C. Johnson and Henry
Jasik, Chapter 29, Page 34) refers to the configuration as a Lindenblad
array, without being specific about the way the dipoles are driven.
However, applying new names to antennas that exploit well known
configurations seems fairly commonplace in the professional field,
particularly in broadcasting.

Of course you can name your antenna as you please, but there might be some
value in mentioning that it is a development of the Lindenblad array - you'd
certainly need to demonstrate awareness of, and distinction from, the prior
art if you were to seek a patent.

Chris

Interesting article, it describes the Lindenblat array as a quartet of
coaxial horns. *Not the same as a quartet of dipoles at all.

Actually, it's not much different.. Both are radiators that radiate a
linearly polarized signal. The Lindenblad (and variants) make the CP
with two dipoles canted relative to each other and fed with a phase
shift (same idea as crossed yagis for Satellite CP antennas). The "two
dipole" thing radiates in both directions, of course. Add another pair
pointing at 90 degrees from the first, and you get roughly
omnidirectional coverage. You can do the same thing with 4 (or 3 or
27) CP horns arranged in a circle.

Most of the fooling around with dimensions and spacing and phasing has
to do with the overall pattern and just how circular it is at which
look angles.

"christofire" wrote in message
...

"Jerry" wrote in message
...

"JosephKK" wrote in message
...
On Mon, 16 Feb 2009 18:49:47 GMT, "Jerry"
wrote:


"JosephKK" wrote in message
m...
On Tue, 10 Feb 2009 18:12:26 -0000, "christofire"
wrote:


"Jerry" wrote in message
...

snip

Chris

Interesting article, it describes the Lindenblat array as a quartet of
coaxial horns. Not the same as a quartet of dipoles at all.


Hi Joseph

I sent an E-mail to the address shown as yours in this group. I use
EZNEC and have lots of files on various sizes and shapes of the DCA and
other OmniAzimuth and Hemispheric coverage antennas. I'd be happy to
share
them with you if you E-mail me directly.
I figure it will benefit me to see the facts and data that shows where
I
am mistaken about how the DCA better than the other hemispheric coverage
antennas for LEO use. It is likely that I have overlooked something.
maybe the DCA can be improved.

Jerry KD6JDJ

Jerry KD6JDJ

I can retrieve the email. Thanks for the notice.

I have done a bit of gedanken after the slant range issue was raised.


A


B



o H
ooo
ooooo

Let the group of "o" represent a polar view of earth,
"A" represent satellite at azimuth (highest point in the sky),
"B" represent satellite between azimuth and horizon,
"Z" represent satellite very near the horizon,
nominal orbital height 1000 miles above mean surface,
and mean radius of earth of 4000 miles.
Then range to the satellite at A is about 1000 miles, at B may be
about 3000 miles and at H would be about 5000 miles. The arithmetic
for relative sensitivity versus elevation angle can even be solved
analytically, though 4 evenly spaced angles on either side of azimuth
would be quite sufficient to plot the most even EIRP curves.
Your DCA is notably more hemispherical than that. Can you tinker it
up to get about 16 dB more at the horizon than at the azimuth?

Hi Joseph

I am not familiar with all the satellite orbits. It seems that most of
the Polar Orbiting Satellites are about 500 miles above the Earth. If
the Earth radius can be considered to be 4,000 miles, the distance to the
satellite at the horizon is about 2,000 miles. That means that, the path
los from the satellite to the ground station varies by about 12 dB as it
passes overhead.
One of the objectives of the DCA design project was to produce a pattern
with about 12 dB less sensitivity toward zenith. I attempted to achieve
that pattern shape by tilting the dipoles to minimize overhead
sensitivity. Serindipity offered me a side benefit when it made me aware
that tilting the dipoles in this array effects the dipole input
impedance. The input impedance of the dipoles in a DCA with 45 degree
tilt (90 degree cross) is about 72 ohms. The dipole input impedance in
a DCA with 30 degree tilt is very near 50 ohms. Kinda lucky!!

Jerry KD6JDJ


... but, dare I ask, what does that do to the axial ratio? Indeed, what
kind of axial ratio is being sought in this application? ... 3 dB or more?

Chris


Hi Chris

I can send you an EZNEC file that includes DCA axial ratio for all angles
within the hemisphere. Or, tell me the angle and I'll tell you the AR.
I developed the DCA for reception from NOAA Polar orbiting satellites on
the 137 MHz band. The axial ratio is not a requirement. The sensitivity
of the antenna to signals from satellites at low elevation angles is a
primary problem. Zero dB axial ratio RHCP antenna is certainly a benefit
for increased sensitivity to weak signals from the satellites.

Jerry KD6JDJ