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#1
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HFTA-ARRL-Space
Tried to make the subject grab a bit.
I just fininshed the ARRL Antenna Book Chapter on Effects of Ground. There are HFTA graphs showing elevation response for various antenna configurations (mostly Yagis). Most arrays show good response up to 12 degrees above the horizon, then many show a null and then, a second peak around 25 to 30 degrees above the horizon. Here's my question: At 25 to 30 degrees elevation response, aren't these waves leaving the ionosphere (i.e., refracted instead of reflected)? Am I right to consider this component of propagation to have left the earth? This would indicate a substantial fraction of each amateur transmission is sent into space. I always thought Broadcast transmissions were most likely to emanate from Earth. Are hams more or less likely to transmit into space than Broadcast? John (who wishes to remain a student and never an expert) |
#2
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HFTA-ARRL-Space
On Sat, 01 Jul 2006 11:09:22 -0400, jawod wrote:
Here's my question: At 25 to 30 degrees elevation response, aren't these waves leaving the ionosphere (i.e., refracted instead of reflected)? In your HFTA program run the antennas at various heights. Amongst other things,varying the height of the antenna will change the elevation angle of the lobes. Danny, K6MHE |
#3
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HFTA-ARRL-Space
On Sat, 01 Jul 2006 11:09:22 -0400, jawod wrote:
Here's my question: At 25 to 30 degrees elevation response, aren't these waves leaving the ionosphere (i.e., refracted instead of reflected)? Hi John, You are confusing models of propagation with models for antenna lobe characteristics. The lobes certainly have a major impact on propagation, but the antenna modeler is not concerned with that. The terrain modeler is not a propagation modeler. For that, consult VOACAP or WINCAP. They are properly concerned with ionospheric issues, but they are also driven by antenna models too. Am I right to consider this component of propagation to have left the earth? To some degree, yes, but it has very little bearing on what you are focused on here. This would indicate a substantial fraction of each amateur transmission is sent into space. In fact, no. The apportionment of the energy into lobes is simply robbing Peter to pay Paul. The nulls were developed from energy lost to the peaked lobes. This is very loose analogy because energy was never lost, it is merely the combination from many sources that makes this lobe shape appears as it does. An antenna radiates from every portion of its structure and in every direction. When all contributions are viewed from a distance, some portions of the structure are out of phase with respect to others portions. When those two contributions are 180° out of phase, that remote point at where they combine perceives a null (a destructive combination). At some other remote point, those same two contributions may combine constructively for a peak response. Same energies all around, but path lengths shift the wave phases and how they combine constructs the characteristic lobe shape. If you took college physics, you must have seen how two charges separated by a distance combine their effects at remote points to offer an "electric dipole." Same logic. 73's Richard Clark, KB7QHC |
#4
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HFTA-ARRL-Space
Hi Richard,
It's good to see you are NOT using Queen Elizabeth the First's, Shakespear's poetical, but somewhat difficult to understand language. Inapropriate for technical matters. There must be other newsgroups available to people who enjoy writing sonnets. As we always knew by reading, with difficulty, between the lines, you are an exceptionally knowledgeable person. Please keep up the good work by continuing to use modern American English, as demonstrated in your last valuable contribution. Thank you. ---- Yours, Punchinello |
#5
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HFTA-ARRL-Space
On Sat, 1 Jul 2006 18:15:01 +0100, "Reg Edwards"
wrote: It's good to see you are NOT using Queen Elizabeth the First's, Shakespear's poetical, but somewhat difficult to understand language. Hi Reggie, I reserve that for the technical Falstaffs. Inapropriate for technical matters. Their usual plea is "discretion is the better part of a direct answer...." As such, technical matters are notably absent, or at best serving as a stalking horse. For those who are shy in their English skills, "stalking horse" finds its current usage in "trolling." 73's Richard Clark, KB7QHC |
#6
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HFTA-ARRL-Space
Richard,
I have NEVER considered your contributions to be deliberate trolling. You just can't help mixing up your desire to produce poetry with your desite to spread technical enlightonment. The two don't mix very well. I am 3/4 of the way down a bottle of "Cotes du Rhone Villages" red, 2004, 14.5% by volume. (I have a great liking for our near neighbours, the French.) So please excuse me if my psycho-analysis is not exactly as you might perceive it yourself. ---- Yours, Punchinello. |
#7
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HFTA-ARRL-Space
On Sat, 1 Jul 2006 19:50:43 +0100, "Reg Edwards"
wrote: I am 3/4 of the way down a bottle of "Cotes du Rhone Villages" red, I've seen a varietal called "Goats do Roam" 2004, 14.5% by volume. YOW! (I have a great liking for our near neighbours, the French.) An empty bottle of Quadrupel "Three Philosophers" Belgian lambic ale (9.8%) sits nearby. So please excuse me if my psycho-analysis is not exactly as you might perceive it yourself. No, our both having included quantifiables from bench testing allows us to add to the topic. 73's Richard Clark, KB7QHC |
#8
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HFTA-ARRL-Space
Richard Clark wrote:
On Sat, 01 Jul 2006 11:09:22 -0400, jawod wrote: Here's my question: At 25 to 30 degrees elevation response, aren't these waves leaving the ionosphere (i.e., refracted instead of reflected)? Hi John, You are confusing models of propagation with models for antenna lobe characteristics. The lobes certainly have a major impact on propagation, but the antenna modeler is not concerned with that. The terrain modeler is not a propagation modeler. For that, consult VOACAP or WINCAP. They are properly concerned with ionospheric issues, but they are also driven by antenna models too. Am I right to consider this component of propagation to have left the earth? To some degree, yes, but it has very little bearing on what you are focused on here. This would indicate a substantial fraction of each amateur transmission is sent into space. In fact, no. The apportionment of the energy into lobes is simply robbing Peter to pay Paul. The nulls were developed from energy lost to the peaked lobes. This is very loose analogy because energy was never lost, it is merely the combination from many sources that makes this lobe shape appears as it does. An antenna radiates from every portion of its structure and in every direction. When all contributions are viewed from a distance, some portions of the structure are out of phase with respect to others portions. When those two contributions are 180° out of phase, that remote point at where they combine perceives a null (a destructive combination). At some other remote point, those same two contributions may combine constructively for a peak response. Same energies all around, but path lengths shift the wave phases and how they combine constructs the characteristic lobe shape. If you took college physics, you must have seen how two charges separated by a distance combine their effects at remote points to offer an "electric dipole." Same logic. 73's Richard Clark, KB7QHC Thanks for setting me right! John AB8WH |
#9
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HFTA-ARRL-Space
Whether you call it Refraction or Reflection hardly matters.
What matters is that the wave, in effect, is reflected from an ionospheric layer at at a particular height, roughly according to optical laws. Trigonometry Rules! Since the transmitted 'beam' has a very wide angle in the vertical plane, the energy returns to earth over an even wider range of distances. The 'elevation angle' reported by antenna simulation programs is not very meaningfull. It contains very little useful information, mainly because the height of a reflecting layer is unknown at the time of transmission. Neither is the number of hops known to a particular destination. ---- Reg. |
#10
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HFTA-ARRL-Space
Reg Edwards wrote:
Whether you call it Refraction or Reflection hardly matters. This I don't understand. To me, refraction versus reflection IS the issue. In optics, Brewster's angle is used. I still don't quite understand thte PseudoBrewster's Angle...it seems to have a different definition (at least in the ARRL book). What matters is that the wave, in effect, is reflected from an ionospheric layer at at a particular height, roughly according to optical laws. Trigonometry Rules! Since the transmitted 'beam' has a very wide angle in the vertical plane, the energy returns to earth over an even wider range of distances. The 'elevation angle' reported by antenna simulation programs is not very meaningfull. It contains very little useful information, mainly because the height of a reflecting layer is unknown at the time of transmission. Neither is the number of hops known to a particular destination. ---- Reg. Reg, Thanks for your answer. I guess I was trying to get at how much ham radio is propagated into space. Certainly SOME does. How does this compare to that amount propagated into space by Broadcast? My assumption has been that VHF TV, etc is easily passed through the ionosphere (minimally refracted). |
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