"Michael Coslo" wrote in message
...
JB wrote:

I don't know if you have seen CATV hardline with a tank strapped to the
utility pole. That keeps water out by pressurizing the hardline. CATV
systems DO have problems with corrosion all the time. With all that
cable
though, the cost to get it up and running is enormous, and they would
rather
be complaint driven instead. They also use circulators so that the
stuff
people do in their house doesn't feed back into the system and screw all
the
other customers up.

Ever open up a cable amp that has had leaky (water type leaky) coax
dripping into it? Yikes, they usually keep working for a while, with all
kinds of electrolyzing going on. It's a pretty sad sight.


- 73 de Mike N3LI -

I've seen boxes of them. I wish I had pictures of the Micor mobile that was
parked in a supervisors car in the middle of a river for 3 days. The
battery went dead making green slime. The only money they had in the budget
was for repair, so we bid them to replace every board. The Mastr Exec had a
Relay and worked fine after drying it out. Things like that are hard to
explain.

Say R56 and it usually covers everything that matters. Check this out.
Use
to take care of a bunch of UHF Micors he


http://eecue.com/images_archive/eecu..._Antennas.html
(no i didn't take the picture)

Much better photos he
http://www.fybush.com/sites/2005/site-051216.html

Jerry wrote:

Hi Jim

It isnt clear to me that you read Howard Kowall's original post. He
intends to build his own antenna to communicate with low earth orbiting
satellites. I have information that will allow Howard to design and build
his own antenna that performs better than the design he chose (Lindenblad).
Do you disagree that a DCA will perform better than a Lindenblad?

Nope.. haven't actually looked at it. BUT.. the thing I was pointing out
is looking at the overall system design, (for which design complexity
and tolerances are factors that need to be considered), it might not matter.


I have read many of your post and recognize that you are a smart guy with
lots of information about antennas. Thats why I wonder why you'd write
something as stupid as " And, for that matter CP is probably not worth
worrying about". You know that 3dB *is* normally something to try to
achieve while building an antenna.

Not if you've got plenty of link margin already, or if there's an easier
way to get the margin (e.g. rather than get 3dB more on the antenna,
shorten the feedline from 100 ft, etc.). Howard didn't say which 2m
satellite he's looking to listen to, or what kind of receiver he's using.


The reason you write that the circular
polarization is minimally significant seems to be that you are attempting to
minimize the value of the DCA. I wonder if you have any facts or data,
measured or calculated, to demonstrate that you know of any antenna that
performs better than a DCA for ground based reception from LEOs

Nope, that's not what I said. What I said was that sometimes, striving
for perfect axial ratio isn't worth it. A linear antenna will have 3dB
loss against a perfect CP, and that's a worst case. It might well be
that 3dB is ok (for receiving WESAT on 137 MHz, for instance, where they
have pretty big EIRP, it wouldn't matter)




I agree with you that a Turnstile is a good antenna for LEO satellite
communication from Earth. But, I also claim that a DCA will perform better
than a Turnstile. Do you disagree?

No, I don't disagree or agree. Don't know how well a DCA does or
doesn't do.


Can you tell me more about why you wrote "For LEO satellites, you don't
really want a hemispherical pattern anyway. You want something with more
gain at the horizon where the slant range is much greater (thousands of
km) than at zenith (where the range is hundreds of km). That is precisely
what I tried to address in the QST article. That is precisely why the
DCA performs better than all others. Besides, the DCA is relatively easy
to build , unlike the Quad helix.

My comment was general, on what sorts of patterns one might want for a
satellite antenna in a fixed position to communicate with LEO.

And, yes, your DCA is easy to build and probably non-critical in
dimensions and tolerances (have you checked this? either by modeling or
measurement?) But so is a turnstile or a turnstile with reflector or a
Lindenblad or even a quad helix, depending on how much variability
you're willing to tolerate

I will readily concede that building a quad helix for VHF is a
mechanical problem, compared to say, 1.5 GHz for GPS. It's going to be a
physically large structure (about the size of two gallon paintcans
stacked), but if you have a cookbook design (as in, buy X feet of
aluminum rod or copper wire, wind it around a plastic trash can, etc.)

I've built monofilar and quad helixes (and Lindenblads and turnstiles)
using copper foil tape on plastic buckets, rolled up paper, and all
sorts of things. Some work better than others, but mostly, it's
mechanical issues that are important. The "RF performance" is pretty
much the same for a given physical size. After all, for an "omni" sort
of antenna close to the ground, there's lots of other factors that
probably have a bigger effect. (which was where I started..)



Again, do you know of any antenna design that performs better than a DCA
for communication with LEOs from earth and doesnt require pointing?


How does one define "better"?

Is your article in QST posted somewhere? Got a NEC deck? (Can't get it
from ARRL because it's too new). Or, heck, rough dimensions and angles,
and I can build the NEC model. (googling KD6JDJ DCA doesn't turn up
anything useful.)

As you know, it's very challenging to get CP with good axial ratio in
all directions (sort of an extension of the hairy ball theorem). For
that matter, the axial ratio of the signal you're receiving may not be
all that hot.

Taking GPS as an example, the SVs have a spec that the axial ratio is no
worse than 1.2dB within 14.3 degrees of boresight for L1, and 3.2 dB for L2.

I couldn't find any convenient data on ham satellite antennas. I think
AO51 uses some variant of a turnstile with separate ports for the two
transmitters, so one is LHCP the other RHCP. I did find a rough link
budget for AO51 (aka Echo) that shows path loss varying by about 8-9 dB
from zenith to horizon.

If we look at state of the art (at least in the 70s) for deep space
exploration, the Low Gain Antenna on Galileo (CP for 2.3GHz) had an
axial ratio of 2dB on boresight, and 11dB at 90 degrees off boresight.
See Bill Imbriale's book at
http://descanso.jpl.nasa.gov/Monogra...rce_external=0
(Volume 8)

for more details and lots and lots of measurements.



Jim

"Jim Lux" wrote in message
...
Jerry wrote:

Hi Jim

It isnt clear to me that you read Howard Kowall's original post. He
intends to build his own antenna to communicate with low earth orbiting
satellites. I have information that will allow Howard to design and
build his own antenna that performs better than the design he chose
(Lindenblad).
Do you disagree that a DCA will perform better than a Lindenblad?

Nope.. haven't actually looked at it. BUT.. the thing I was pointing out
is looking at the overall system design, (for which design complexity and
tolerances are factors that need to be considered), it might not matter.


I have read many of your post and recognize that you are a smart guy
with lots of information about antennas. Thats why I wonder why you'd
write something as stupid as " And, for that matter CP is probably not
worth worrying about". You know that 3dB *is* normally something to try
to achieve while building an antenna.

Not if you've got plenty of link margin already, or if there's an easier
way to get the margin (e.g. rather than get 3dB more on the antenna,
shorten the feedline from 100 ft, etc.). Howard didn't say which 2m
satellite he's looking to listen to, or what kind of receiver he's using.


The reason you write that the circular
polarization is minimally significant seems to be that you are attempting
to minimize the value of the DCA. I wonder if you have any facts or
data, measured or calculated, to demonstrate that you know of any antenna
that performs better than a DCA for ground based reception from LEOs

Nope, that's not what I said. What I said was that sometimes, striving
for perfect axial ratio isn't worth it. A linear antenna will have 3dB
loss against a perfect CP, and that's a worst case. It might well be that
3dB is ok (for receiving WESAT on 137 MHz, for instance, where they have
pretty big EIRP, it wouldn't matter)




I agree with you that a Turnstile is a good antenna for LEO satellite
communication from Earth. But, I also claim that a DCA will perform
better than a Turnstile. Do you disagree?

No, I don't disagree or agree. Don't know how well a DCA does or doesn't
do.


Can you tell me more about why you wrote "For LEO satellites, you
don't
really want a hemispherical pattern anyway. You want something with more
gain at the horizon where the slant range is much greater (thousands of
km) than at zenith (where the range is hundreds of km). That is
precisely what I tried to address in the QST article. That is
precisely why the DCA performs better than all others. Besides, the
DCA is relatively easy to build , unlike the Quad helix.

My comment was general, on what sorts of patterns one might want for a
satellite antenna in a fixed position to communicate with LEO.

And, yes, your DCA is easy to build and probably non-critical in
dimensions and tolerances (have you checked this? either by modeling or
measurement?) But so is a turnstile or a turnstile with reflector or a
Lindenblad or even a quad helix, depending on how much variability you're
willing to tolerate

I will readily concede that building a quad helix for VHF is a mechanical
problem, compared to say, 1.5 GHz for GPS. It's going to be a physically
large structure (about the size of two gallon paintcans stacked), but if
you have a cookbook design (as in, buy X feet of aluminum rod or copper
wire, wind it around a plastic trash can, etc.)

I've built monofilar and quad helixes (and Lindenblads and turnstiles)
using copper foil tape on plastic buckets, rolled up paper, and all sorts
of things. Some work better than others, but mostly, it's mechanical
issues that are important. The "RF performance" is pretty much the same
for a given physical size. After all, for an "omni" sort of antenna close
to the ground, there's lots of other factors that probably have a bigger
effect. (which was where I started..)



Again, do you know of any antenna design that performs better than a
DCA for communication with LEOs from earth and doesnt require pointing?


How does one define "better"?

Is your article in QST posted somewhere? Got a NEC deck? (Can't get it
from ARRL because it's too new). Or, heck, rough dimensions and angles,
and I can build the NEC model. (googling KD6JDJ DCA doesn't turn up
anything useful.)

As you know, it's very challenging to get CP with good axial ratio in all
directions (sort of an extension of the hairy ball theorem). For that
matter, the axial ratio of the signal you're receiving may not be all that
hot.

Taking GPS as an example, the SVs have a spec that the axial ratio is no
worse than 1.2dB within 14.3 degrees of boresight for L1, and 3.2 dB for
L2.

I couldn't find any convenient data on ham satellite antennas. I think
AO51 uses some variant of a turnstile with separate ports for the two
transmitters, so one is LHCP the other RHCP. I did find a rough link
budget for AO51 (aka Echo) that shows path loss varying by about 8-9 dB
from zenith to horizon.

If we look at state of the art (at least in the 70s) for deep space
exploration, the Low Gain Antenna on Galileo (CP for 2.3GHz) had an axial
ratio of 2dB on boresight, and 11dB at 90 degrees off boresight.
See Bill Imbriale's book at
http://descanso.jpl.nasa.gov/Monogra...rce_external=0
(Volume 8)

for more details and lots and lots of measurements.



Jim

Hi Jim

I wont interlace my reply so that it might be easier for us to read.

You wrote that "it might not matter that a DCA performs better than a
Lindenblad" Well it does perform better for contact with a LEO satellite
and I'd expect that be enough to make the DCA worth considering. Maybe I am
missing something. Why would you *not* try making DCA for LEOs??

What (exactly is your point in writing about eliminating line loss when
the discussion is antenna sensitivity??? Why is it pertinent what LEO he
is interested in or what receiver he uses??? He asked about coax for an
antenna harness. I thought I was helping Howard when I pointed him toward
the DCA. Jim, if you dont need the DCA design concept there is no need for
you to consider it. But, please dont diminish the value of the DCA for
LEO use unless you have facts or data to show where I'm wrong about how well
the DCA performs.

Jim, are you writing that antenna sensitivity "doesnt matter" when
receiving NOAA weather satellite signals at 137-138 MHz? If so you are
completely wrong. Oh, you personally may have no interest in reception
from the NOAA satellites (APT) as low elevations. but, when recording
images of the Earth from NOAA satellites (APT) there is *no* antenna that
performs better than a DCA. And, that extra sensitivity using the DCA is
highly desired by most APT imagers.

Yes, I have made lots of measurements of the DCA. I made my own slotted
line so I could know the antenna's impedance. I have hundreds of actual
(measured) radiation patterns. I have plenty of EZNEC models of the DCA.
As I posted earlier, Patrik Tast posts lots of fundamental design
information on his Web Site http://www.poes-weather.com/index.php .
Clearly, I am proud of the results I have realized with this DCA antenna
design project, so I'm always happy to share it with anyone interested.
Anyone interested in the DCA has always received answers to any/all
questions sent to me.

I define better performance as greater sensitivity to signals from LEO
satellites. But, the DCA has a much wider impedance match than a Quad
Helix.

I was pleasantly surprised that the axial ratio of the DCA radiation is
exceptionally good at most angles. EZNEC gives good prediction of AR at all
angles. Patrik Tast's Signal Plotter records the antenna sensitivity at 1
second intervals while the NOAA satellite is above the horizon. As I
remember, you acknowledged that I have developed a method of recording
actual radiation patterns using the program Patrik developed for me
(SignalPlotter).
I submit to you that, if you ever have need to develop a hemispheric
coverage antenna for CP signals, you could benefit from learning about the
DCA. It works.

Jerry KD6JDJ (who sincerely wants to know
facts about the flaws in the DCA design)

"Dave Platt" wrote in message
...

snip

I don't think there's any problem with using these sorts of cables in
commercial or amateur service in *simplex* applications... they can
handle transmitting, or receiving, just fine. It's only when you try
to do both, simultaneously, through the same cable. that the noise
generation can become a problem.

The same can be true of some classes of antenna problems. The
repeater system I help maintain developed a serious desensitization
problem, due to internal corrosion/oxidation which occurred in the
antenna after several years up in the weather. I doubt that the
corrosion/oxidation effect would ever have been noticed if the antenna
were in service as a normal (simplex) base antenna - it didn't affect
the transmit SWR or the receive sensitivity at all,

All metallic contacts are potential problems. For years I did Navy
electronics, including a couple hundred EMI inspections. Where "topside
housekeeping" was neglected, broadband noise (BBN) was sure to be a problem.
(All topside metallic objects need to be either insulated or firmly
connected -- no incidental contact.)

As little as a hundred watts would excite some junctions to generate BBN
that could be detected throughout the HF band on other antennas. More power
would generate BBN up to several hundred MHz. Been there.

All metallic contacts are potential problems. For years I did Navy
electronics, including a couple hundred EMI inspections. Where "topside
housekeeping" was neglected, broadband noise (BBN) was sure to be a
problem.
(All topside metallic objects need to be either insulated or firmly
connected -- no incidental contact.)

As little as a hundred watts would excite some junctions to generate BBN
that could be detected throughout the HF band on other antennas. More
power
would generate BBN up to several hundred MHz. Been there.

Great point!
My worst problem was my TV antenna mast, 20' away from my Butternut.
Actually generated TVI until I replaced it all, including all brackets and
hardware. Most of my neighbors TV antenna systems look far worse for wear.
I have offered free labor to replace for surrounding neighbors and was taken
up on it by one who had never seen so many stations before. It seems to be
something that people don't do right anymore because no one will pay for it.

On Tue, 10 Feb 2009 07:57:28 GMT, "Jerry"
wrote:


"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


I would be interested in seeing what NEC would make of one of these.

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...B_antennas.pdf )
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.

"JosephKK" wrote in message
...
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...B_antennas.pdf
)
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.


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

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?