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#1
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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 |
#2
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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 |
#3
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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
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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
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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
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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 |
#7
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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
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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
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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
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"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 |