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Old October 13th 04, 04:44 PM
Thierry
 
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Default Discone and quadrifilar helix ?

Hi,

To pick up a 137 MHz signal from wx satellite (POES), are the discone and
quadrifilar helix antennas similar, I mean, they are different in design but
for the rest ?
Are they both omnidirectional and are they both able to change automatically
the elevation and azimuth to the satellite direction without interruption
and without requiring a rotator ? or only the helix provides this capability
?

Thanks in advance

Thierry, ON4SKY
http://www.astrosurf.com/lombry



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Old October 13th 04, 05:16 PM
Fractenna
 
Posts: n/a
Default

Hi,

To pick up a 137 MHz signal from wx satellite (POES), are the discone and
quadrifilar helix antennas similar, I mean, they are different in design but
for the rest ?
Are they both omnidirectional and are they both able to change automatically
the elevation and azimuth to the satellite direction without interruption
and without requiring a rotator ? or only the helix provides this capability
?

Thanks in advance

Thierry, ON4SKY
http://www.astrosurf.com/lombry


A discone is a wideband, upside down, vertical monopole, essentially. It has
poor coverage at high elevations. It is omniazimuth.

Why would you need a discone? It's chosen for its bandwidth, and you don't
appear to have this as a requirement. Also its fairly good sized, even for the
skeleton ones.

73,
Chip N1IR
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Old October 13th 04, 06:51 PM
Roy Lewallen
 
Posts: n/a
Default

A discone antenna is a vertically polarized, broad bandwidth antenna. A
quadrifilar helix is a circularly polarized, relatively narrow bandwidth
antenna. About the only thing they have in common is that both are
omnidirectional in azimuth. A quadrifilar helix is a more suitable
antenna for receiving the circularly polarized, relatively narrow
bandwidth signals from a weather satellite.

Roy Lewallen, W7EL

Thierry wrote:
Hi,

To pick up a 137 MHz signal from wx satellite (POES), are the discone and
quadrifilar helix antennas similar, I mean, they are different in design but
for the rest ?
Are they both omnidirectional and are they both able to change automatically
the elevation and azimuth to the satellite direction without interruption
and without requiring a rotator ? or only the helix provides this capability
?

Thanks in advance

Thierry, ON4SKY
http://www.astrosurf.com/lombry



  #4   Report Post  
Old October 13th 04, 08:13 PM
Thierry
 
Posts: n/a
Default

This is to receive WX APT signal on 137 Mhz and sometimes to work on VHF or
listen to avi band.
According you 'd it be interested or not at all to select a discone instead
of the helix ?
There is no advantage of using a discone, or even drawbacks vs. the helix,
excepted the price ?

Thierry


"Roy Lewallen" wrote in message
...
A discone antenna is a vertically polarized, broad bandwidth antenna. A
quadrifilar helix is a circularly polarized, relatively narrow bandwidth
antenna. About the only thing they have in common is that both are
omnidirectional in azimuth. A quadrifilar helix is a more suitable
antenna for receiving the circularly polarized, relatively narrow
bandwidth signals from a weather satellite.

Roy Lewallen, W7EL

Thierry wrote:
Hi,

To pick up a 137 MHz signal from wx satellite (POES), are the discone

and
quadrifilar helix antennas similar, I mean, they are different in design

but
for the rest ?
Are they both omnidirectional and are they both able to change

automatically
the elevation and azimuth to the satellite direction without

interruption
and without requiring a rotator ? or only the helix provides this

capability
?

Thanks in advance

Thierry, ON4SKY
http://www.astrosurf.com/lombry





  #5   Report Post  
Old October 13th 04, 08:32 PM
Fractenna
 
Posts: n/a
Default

There is no advantage of using a discone, or even drawbacks vs. the helix,
excepted the price ?


Discone is not the right antenna for this app.

QF helix is good, so is a 2 turn Kraus helix, or a cp patch.

Crossed dipoles in quadrature acceptable in most cases too.

73,
Chip N1IR


  #6   Report Post  
Old October 13th 04, 10:33 PM
G.Beat
 
Posts: n/a
Default

Here is a good web site for building a quadfilar helix antenna

http://www.qsl.net/kf4cpj/qha/

"Thierry" - wrote in message ...

This is to receive WX APT signals broadcast on 137 Mhz and sometimes to
listen to
the aviation band or work VHF (144 - 146 MHz - amateur allocation).
Should I select a discone instead of the helix ?
Are there any advantages of using a discone, or drawbacks, versus a
quadrifilar helix
antenna, except the price ?

Thierry


"Roy Lewallen" wrote in message
...
A discone antenna is a vertically polarized, broad bandwidth antenna. A
quadrifilar helix is a circularly polarized, relatively narrow bandwidth
antenna. About the only thing they have in common is that both are
omnidirectional in azimuth. A quadrifilar helix is a more suitable
antenna for receiving the circularly polarized, relatively narrow
bandwidth signals from a weather satellite.

Roy Lewallen, W7EL




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Old October 13th 04, 11:51 PM
Roy Lewallen
 
Posts: n/a
Default

The discone would be better for local amateur VHF communication and
listening to the aviation band. The quadrifilar helix would be better
for receiving the weather satellite. If you can only have one antenna,
you have to choose which applications you're willing to accept reduced
performance with.

Roy Lewallen, W7EL

Thierry wrote:

This is to receive WX APT signal on 137 Mhz and sometimes to work on VHF or
listen to avi band.
According you 'd it be interested or not at all to select a discone instead
of the helix ?
There is no advantage of using a discone, or even drawbacks vs. the helix,
excepted the price ?

Thierry

  #8   Report Post  
Old October 14th 04, 05:58 AM
Walter Maxwell
 
Posts: n/a
Default

On Wed, 13 Oct 2004 15:51:42 -0700, Roy Lewallen wrote:

The discone would be better for local amateur VHF communication and
listening to the aviation band. The quadrifilar helix would be better
for receiving the weather satellite. If you can only have one antenna,
you have to choose which applications you're willing to accept reduced
performance with.

Roy Lewallen, W7EL


Roy is right. However, I'd like to steer you to another reference that will take
you back to the original work on the QFH for satellite use.

I performed the original research that led to the use of the QFH as the primary
radiators on all TIROS-N, NOAA polar orbiting satellites. As the lead engineer
at RCA Astro's antenna laboratory, I measured the radiation patterns and
terminal impedances on more than 1000 different electrical and mechanical
configurations of the QFH antenna. Of those many patterns one was chosen for the
NOAA satellites based on consistant, continous, solid contact with all ground
stations from the time the spacecraft was 10 degrees above the horizon.

The QFH configuration used on the NOAA polar orbiting spacecrafts comprise two
bifilar helices spaced in quadrature around the axis, and fed in quadrature (90
degree) relationship. Quadrature feed is necessary to obtain the circular
polarization required to achieve continuous, solid contact with the ground
stations, both in receive and transmit operations.

I have documented the R&D research I performed at RCA in 1973 in my book
"Reflections--Transmission Lines and Antennas--2." It appears on my web page at
http://home.iag.net/~w2du, and is available for downloading in PDF format..

A copy of my research report appears in Appendix 13, which explains the
procedure I used in measuring the more than 1000 configurations of the QFH
antenna.

A Smith Chart plot of the terminal impedances of two configurations appears in
the research report as Figs 9 and 10.

The radiation patterns of three configurations of the QFH appear in Figs 5, 6,
and 7. The electrical and mechanical configurations are defined in the legend
box in the upper right hand corner of the pattern charts.

The pattern shown in Fig 5 is that of the configuration used on all TIROS-N,
NOAA polar orbiting satellites for the 1.6 GHz wide-band video frequency.

A detailed discussion of the QFH principles of operation and the mechanical
construction of two different configurations is also presented in Reflections 2,
Chapter 22. The space-craft-to-ground SAR relay frequency is1.9 GHz, and the
wx frequency is 137 MHz. The QFH gets a real workout on this class of wx
spacecraft. The description of the 1.9 GHz SAR relay antenna appears in Sec 22.5
beginning on Page 22.7, with radiation patterns appearing in Figs 22-5 and 22-6.
This feed configuration used with this antenna is the infinite balun, as shown
in Fig 22-8, and described in Sec 22.8.

It is now time to refer to Gate's reference, http://www.qsl.net/kf4cpj/qha/, It
appears to me that a vital element is missing in the description appearing in
this reference--the means for achieving circular polarization. He shows long and
short bifilar elements, necessary for self-phasing of the bifilar elements to
achieve the circular polarization, but the feed method to achieve the CP appears
to be missing. For this reason I have a solid feeling that this QFH is not
radiating CP.

In my discussion in Chapter 22 I explain the self-phasing method in detail, and
I also show theSmith-Chart plot of the impedance pattern that must appear to
prove that the 90-degree phasing between the two bilfilar elements is achieved.
That plot is shown in Fig 22-10, which shows the cusp of the pattern at 50 + j0
a the operating frequency. It was found by measurements made on many QFH
antennas using this configuration that when the point of the cusp appears at 50
+ j0, the correct 90-degree phasing was achieved and the desired radiation
patterns shown in Figs 22-5 and 22-6 were achieved.

The 1.9 GHz space-craft-to-ground SAR relay antenna uses the self-phased
infinite balun feed.

The dimensions for the self-phased QFH with the infinite balun feed appear on
Page 22-14 in terms of wave-length lambda. It should be noted that the obtain
the self-phasing characteristic the diameter of the radiating elements is
crucial in obtaining the 90-degree relationship between the two bifilar
elements, because the INDUCTANCE of the elements is the effective parameter in
the phasing. The inductance of the short bifilar causes the current flowing in
it to lead by 45 degrees, while the INDUCTANACE in the long bifilar causes its
current to lag by 45 degrees. This phasing relationship requires the diameter of
the radiating elements to be 0.0088 lambda in length for whatever frequency is
used. The legend for the various elements also appears in Figs 22-3 and 22-4.

It should be noted that for use at 137 MHz the diameter is 3/4". I made mine of
3/4" soft copper tubing with standard plumbing hardware, including 90-degree
elbows at the sharp corners and the standard T at the bottom center.

I hope this helps you 137 MHz wx buffs in achieving the antenna that will suck
the wx sigs from near horizon to near horizon with no dropouts from the
beginning to the end of the pass, and without adjustment of orientation--just
point it straight up!

Walt Maxwell, W2DU
  #9   Report Post  
Old October 14th 04, 12:37 PM
G.Beat
 
Posts: n/a
Default

John Coppens ON6JC/LW3HAZ, posted a photo (NOAA 17) of a quadrifilar antenna
on his web page.
http://www.jcoppens.com/ant/qfh/index.en.php

g. beat
w9gb


"Walter Maxwell" wrote in message
...
On Wed, 13 Oct 2004 15:51:42 -0700, Roy Lewallen wrote:

The discone would be better for local amateur VHF communication and
listening to the aviation band. The quadrifilar helix would be better
for receiving the weather satellite. If you can only have one antenna,
you have to choose which applications you're willing to accept reduced
performance with.

Roy Lewallen, W7EL


Roy is right. However, I'd like to steer you to another reference that
will take
you back to the original work on the QFH for satellite use.

I performed the original research that led to the use of the QFH as the
primary
radiators on all TIROS-N, NOAA polar orbiting satellites. As the lead
engineer
at RCA Astro's antenna laboratory, I measured the radiation patterns and
terminal impedances on more than 1000 different electrical and mechanical
configurations of the QFH antenna. Of those many patterns one was chosen
for the
NOAA satellites based on consistant, continous, solid contact with all
ground
stations from the time the spacecraft was 10 degrees above the horizon.

The QFH configuration used on the NOAA polar orbiting spacecrafts
comprise two
bifilar helices spaced in quadrature around the axis, and fed in
quadrature (90
degree) relationship. Quadrature feed is necessary to obtain the circular
polarization required to achieve continuous, solid contact with the ground
stations, both in receive and transmit operations.

I have documented the R&D research I performed at RCA in 1973 in my book
"Reflections--Transmission Lines and Antennas--2." It appears on my web
page at
http://home.iag.net/~w2du, and is available for downloading in PDF
format..

A copy of my research report appears in Appendix 13, which explains the
procedure I used in measuring the more than 1000 configurations of the QFH
antenna.

A Smith Chart plot of the terminal impedances of two configurations
appears in
the research report as Figs 9 and 10.

The radiation patterns of three configurations of the QFH appear in Figs
5, 6,
and 7. The electrical and mechanical configurations are defined in the
legend
box in the upper right hand corner of the pattern charts.

The pattern shown in Fig 5 is that of the configuration used on all
TIROS-N,
NOAA polar orbiting satellites for the 1.6 GHz wide-band video frequency.

A detailed discussion of the QFH principles of operation and the
mechanical
construction of two different configurations is also presented in
Reflections 2,
Chapter 22. The space-craft-to-ground SAR relay frequency is1.9 GHz, and
the
wx frequency is 137 MHz. The QFH gets a real workout on this class of wx
spacecraft. The description of the 1.9 GHz SAR relay antenna appears in
Sec 22.5
beginning on Page 22.7, with radiation patterns appearing in Figs 22-5 and
22-6.
This feed configuration used with this antenna is the infinite balun, as
shown
in Fig 22-8, and described in Sec 22.8.

It is now time to refer to Gate's reference,
http://www.qsl.net/kf4cpj/qha/, It
appears to me that a vital element is missing in the description appearing
in
this reference--the means for achieving circular polarization. He shows
long and
short bifilar elements, necessary for self-phasing of the bifilar elements
to
achieve the circular polarization, but the feed method to achieve the CP
appears
to be missing. For this reason I have a solid feeling that this QFH is not
radiating CP.

In my discussion in Chapter 22 I explain the self-phasing method in
detail, and
I also show theSmith-Chart plot of the impedance pattern that must appear
to
prove that the 90-degree phasing between the two bilfilar elements is
achieved.
That plot is shown in Fig 22-10, which shows the cusp of the pattern at 50
+ j0
a the operating frequency. It was found by measurements made on many QFH
antennas using this configuration that when the point of the cusp appears
at 50
+ j0, the correct 90-degree phasing was achieved and the desired radiation
patterns shown in Figs 22-5 and 22-6 were achieved.

The 1.9 GHz space-craft-to-ground SAR relay antenna uses the self-phased
infinite balun feed.

The dimensions for the self-phased QFH with the infinite balun feed appear
on
Page 22-14 in terms of wave-length lambda. It should be noted that the
obtain
the self-phasing characteristic the diameter of the radiating elements is
crucial in obtaining the 90-degree relationship between the two bifilar
elements, because the INDUCTANCE of the elements is the effective
parameter in
the phasing. The inductance of the short bifilar causes the current
flowing in
it to lead by 45 degrees, while the INDUCTANACE in the long bifilar causes
its
current to lag by 45 degrees. This phasing relationship requires the
diameter of
the radiating elements to be 0.0088 lambda in length for whatever
frequency is
used. The legend for the various elements also appears in Figs 22-3 and
22-4.

It should be noted that for use at 137 MHz the diameter is 3/4". I made
mine of
3/4" soft copper tubing with standard plumbing hardware, including
90-degree
elbows at the sharp corners and the standard T at the bottom center.

I hope this helps you 137 MHz wx buffs in achieving the antenna that will
suck
the wx sigs from near horizon to near horizon with no dropouts from the
beginning to the end of the pass, and without adjustment of
orientation--just
point it straight up!

Walt Maxwell, W2DU



  #10   Report Post  
Old October 14th 04, 12:51 PM
Thierry
 
Posts: n/a
Default


"Roy Lewallen" wrote in message
...
The discone would be better for local amateur VHF communication and
listening to the aviation band. The quadrifilar helix would be better
for receiving the weather satellite. If you can only have one antenna,
you have to choose which applications you're willing to accept reduced
performance with.

Roy Lewallen, W7EL


OK Roy, I well understood.
I suspected well this purpose due to its vertical polarization. In fact I
was misleaded by the short radials placed at 45 deg on top. But it is common
and that doesn't differ from a ground plan vertical design, excepted it
offers a large bdw....

Thanks
Thierry, ON4SKY


Thierry wrote:

This is to receive WX APT signal on 137 Mhz and sometimes to work on VHF

or
listen to avi band.
According you 'd it be interested or not at all to select a discone

instead
of the helix ?
There is no advantage of using a discone, or even drawbacks vs. the

helix,
excepted the price ?

Thierry



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