"christofire" wrote in message
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"Jerry" wrote in message
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"christofire" wrote in message
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"Jerry" wrote in message
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"christofire" wrote in message
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"Jerry" wrote in message
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"Harry H" wrote in message
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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


Hi Chris

I wonder if you have any pictures of a Lindenblad and any radiation
plots. I also wonder if an end fire antenna is the same as a broadside
antenna when they look the same from a distance.

Jerry KD6JDJ


You could take a look at www.bbc.co.uk/rd/pubs/reports/1991-15.pdf which
on pages 9 and 10 has some details of a Lindenblad for 2.5 GHz, with
patterns, that was made from semi-rigid coax and brass tube. The aim in
that work was to achieve the best possible axial ratio in order to reject
first-order reflections from the ground and nearby objects. If I remember
correctly, phase rotation was tried but there really weren't enough
variables to get the axial ratio good enough over the whole sphere, so the
dipoles were driven in phase and the hole in the vertical radiation
pattern at the bottom was 'embraced' as a good thing! In this
application, if good axial ratio couldn't be achieved somewhere it was
probably better to avoid radiating in that direction.

Another Lindenblad, but also arrayed vertically in four tiers, was used at
High Hunsley transmitting station for FM radio. The older photos at
http://tx.mb21.co.uk/gallery/high-hunsley.php show it (at the top of the
structure) but they are rather distant. The modern replacements are
basically crossed dipoles in front of reflectors. A significant challenge
in the design of these (big) things is to get the horizontal radiation
pattern to hand over cleanly from one element to the next around the
structure, without lobes or nulls in either the vertical or horizontal
component. In UK Band II broadcasting, the polarisation is usually said
to be 'mixed' rather than intentionally circular. The Alan Dick company
http://www.alandick.com/broadcast_an...roduct_004.htm still offers a
Lindenblad array for Band II. Their 'FMAC' looks interesting!

As to your question, I'm not certain what you mean so perhaps you could
amplify a bit. Certainly if the paths of currents, their relative
amplitudes and their relative phases in time, appear the same from
different directions then the polarisation should be the same in those
directions. A short helix can operate as a broadside and end-fire antenna
at the same time and I know the quadrifilar helix is a popular option for
small L-Band satellite terminals. However, that radio-camera application
imposed stringent demands for axial ratio and, obviously, the requirements
for satisfactory reception of CP signals from satellites can be less
demanding when CP is used simply to avoid loss on account of mismatched
linear polarisations - when the other sense of CP isn't in use at the same
frequency by the same satellite.

Chris


Hi Chris

The Lindenblad antenna is fed to produce a null toward zenith. The
Lindenblad antenna as defined by Brown and Woodward in the mid 1940s for TV
transmission, has an omniazimuth radiation pattern.
The DCA has no zenith null.

If you consider an antenna with an overhead null to be the same as an
antenna with no null to be the same, I have no expectation that you and I
will agree.

The DCA offers little advantage over a Quad Helix when radiation pattern
is considered.
The DCA is slightly more sensitive toward the horizon than the Quad Helix.
..
The bandwidth of a DCA is far wider than a Quad helix.
The DCA is very insensitive to dimensional errors when built by an
amateur. The Quad Helix is extreemely demanding of prescission of
construction.

The original subject of this thread was related to building an antenna for
reception of Low Earth Orbiting satellites. I figured the OP could
appreciate knowing that a DCA will perform better than a Lindenblad and
needs no series matching transformors.

Jerry KD6JDJ