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#1
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Dipoles, why height matters
Ian Jackson wrote:
snip Despite the obvious theory, and over 50 years in amateur radio, I still find it hard to believe that, in real life, an 80m dipole at (say) 20' ever really outperforms (at any distance) one at (say) 100'. Given the choice, I know which one I would choose! Try reading these: http://www.qsl.net/wb5ude/nvis/ http://en.wikipedia.org/wiki/Near_ve...idence_skywave http://www.w0ipl.net/ECom/NVIS/nvis.htm http://kv5r.com/ham-radio/nvis-antennas/ http://www.arrl.org/nvis -- Jim Pennino |
#3
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Dipoles, why height matters
Ian Jackson wrote:
In message , writes Ian Jackson wrote: snip Despite the obvious theory, and over 50 years in amateur radio, I still find it hard to believe that, in real life, an 80m dipole at (say) 20' ever really outperforms (at any distance) one at (say) 100'. Given the choice, I know which one I would choose! Try reading these: http://www.qsl.net/wb5ude/nvis/ http://en.wikipedia.org/wiki/Near_ve...idence_skywave http://www.w0ipl.net/ECom/NVIS/nvis.htm http://kv5r.com/ham-radio/nvis-antennas/ http://www.arrl.org/nvis Thanks, I'll certainly have a good read of those articles. But regardless of what they say, in a typical amateur scenario, I still reckon that at (say) 300 miles, an 80m signal from a dipole at 100' is likely to be stronger than one from one at 20' (or even at 60'). As 300 miles is at the upper end of NVIS and the lower end for skywave, it would be a crap shoot. NVIS distance is typically 30-400 miles. -- Jim Pennino |
#4
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Dipoles, why height matters
In message ,
writes Ian Jackson wrote: In message , writes Ian Jackson wrote: snip Despite the obvious theory, and over 50 years in amateur radio, I still find it hard to believe that, in real life, an 80m dipole at (say) 20' ever really outperforms (at any distance) one at (say) 100'. Given the choice, I know which one I would choose! Try reading these: http://www.qsl.net/wb5ude/nvis/ http://en.wikipedia.org/wiki/Near_ve...idence_skywave http://www.w0ipl.net/ECom/NVIS/nvis.htm http://kv5r.com/ham-radio/nvis-antennas/ http://www.arrl.org/nvis Thanks, I'll certainly have a good read of those articles. But regardless of what they say, in a typical amateur scenario, I still reckon that at (say) 300 miles, an 80m signal from a dipole at 100' is likely to be stronger than one from one at 20' (or even at 60'). As 300 miles is at the upper end of NVIS and the lower end for skywave NVIS IS skywave - only that it's more straight up-and-down than at an angle. It's only a matter (literally) of degree, and there's no real point at which NVIS becomes 'normal' skywave. , it would be a crap shoot. NVIS distance is typically 30-400 miles. OK, let's make it a bit less - say 50 or 100 miles. I still feel that, in practice, a dipole at 100' would be unlikely to be less effective than at 20'. On the other hand, if you only want to lay down a signal out to less than 400 miles, there's no point in going to the trouble of putting the dipole at 100'. Apart from cost etc, this would also unnecessarily cause QRM to reception outside your intended target area. -- Ian |
#5
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Dipoles, why height matters
Ian Jackson wrote:
In message , writes Ian Jackson wrote: In message , writes Ian Jackson wrote: snip Despite the obvious theory, and over 50 years in amateur radio, I still find it hard to believe that, in real life, an 80m dipole at (say) 20' ever really outperforms (at any distance) one at (say) 100'. Given the choice, I know which one I would choose! Try reading these: http://www.qsl.net/wb5ude/nvis/ http://en.wikipedia.org/wiki/Near_ve...idence_skywave http://www.w0ipl.net/ECom/NVIS/nvis.htm http://kv5r.com/ham-radio/nvis-antennas/ http://www.arrl.org/nvis Thanks, I'll certainly have a good read of those articles. But regardless of what they say, in a typical amateur scenario, I still reckon that at (say) 300 miles, an 80m signal from a dipole at 100' is likely to be stronger than one from one at 20' (or even at 60'). As 300 miles is at the upper end of NVIS and the lower end for skywave NVIS IS skywave - only that it's more straight up-and-down than at an angle. It's only a matter (literally) of degree, and there's no real point at which NVIS becomes 'normal' skywave. NVIS is generally defined as aiming the power straight up and the S in NVIS stands for "Skywave". So if you want to be pendatic, you are correct. However, if you look at the links above, the real world DOES make a distinction between NVIS and skywave. it would be a crap shoot. NVIS distance is typically 30-400 miles. OK, let's make it a bit less - say 50 or 100 miles. I still feel that, in practice, a dipole at 100' would be unlikely to be less effective than at 20'. The experience of all the world's militaries and those others who have done actual measurements come to a contrary conclusion. -- Jim Pennino |
#6
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Dipoles, why height matters
On Saturday, November 22, 2014 4:01:08 PM UTC-6,
NVIS is generally defined as aiming the power straight up and the S in NVIS stands for "Skywave". So if you want to be pendatic, you are correct. However, if you look at the links above, the real world DOES make a distinction between NVIS and skywave. I'll have to read through them, but myself, I consider any signal which is reflected off the ionosphere back to the target receiver, as being skywave, no matter if the angle is 90 or 10 degrees. If it doesn't use the ionosphere, it's not skywave. Sometimes you can have a mix of path modes. IE: being able to receive both the skywave, but also the ground or space wave. In most cases like that, the NVIS path will overwhelm the ground or space wave unless the two stations are very close together. |
#7
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Dipoles, why height matters
On 11/22/2014 5:33 PM, wrote:
On Saturday, November 22, 2014 4:01:08 PM UTC-6, NVIS is generally defined as aiming the power straight up and the S in NVIS stands for "Skywave". So if you want to be pendatic, you are correct. However, if you look at the links above, the real world DOES make a distinction between NVIS and skywave. I'll have to read through them, but myself, I consider any signal which is reflected off the ionosphere back to the target receiver, as being skywave, no matter if the angle is 90 or 10 degrees. If it doesn't use the ionosphere, it's not skywave. Sometimes you can have a mix of path modes. IE: being able to receive both the skywave, but also the ground or space wave. In most cases like that, the NVIS path will overwhelm the ground or space wave unless the two stations are very close together. You are correct - NVIS is a form of skywave. And it is considered by experts in the field to be a form of skywave (hence the "S" in NVIS), although for much shorter distances than skywaves utilizing a lower angle of radiation. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
#8
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Dipoles, why height matters
On 11/22/2014 7:21 AM, Ian Jackson wrote:
In message , writes Ian Jackson wrote: snip Despite the obvious theory, and over 50 years in amateur radio, I still find it hard to believe that, in real life, an 80m dipole at (say) 20' ever really outperforms (at any distance) one at (say) 100'. Given the choice, I know which one I would choose! Try reading these: http://www.qsl.net/wb5ude/nvis/ http://en.wikipedia.org/wiki/Near_ve...idence_skywave http://www.w0ipl.net/ECom/NVIS/nvis.htm http://kv5r.com/ham-radio/nvis-antennas/ http://www.arrl.org/nvis Thanks, I'll certainly have a good read of those articles. But regardless of what they say, in a typical amateur scenario, I still reckon that at (say) 300 miles, an 80m signal from a dipole at 100' is likely to be stronger than one from one at 20' (or even at 60'). Yes, intuitively it certainly seems like the higher antenna will perform better. However, I have a chart about loop antennas that rates the 75 meter loop highest in NVIS gain at 25 feet high. I included the pdf file if it comes through. Mine at 33 feet makes a pretty good NVIS antenna. Will never know what it would do at 100 feet. |
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