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Dipoles, why height matters
Jerry Stuckle wrote:
On 11/21/2014 8:19 PM, wrote: Jerry Stuckle wrote: snip I've also run dipoles - I got WAS on 75 meters from Iowa with an inverted VEE running from 50' to near ground. And I had a strong signal on the Iowa 75M SSB net. I have lots of strong signal reports from around the country on 6M AM running 3W into a 2 foot collapsible whip. Of course it was at the height of sunspot cycle 19 and says NOTHING about the effectiveness of the antenna. Which has absolutely nothing to do with your comment about a dipole on 75 meters. But you're too stoopid to understand that. But it has EVERYTHING to do with your comment about WAS. But you are so enraged about being correct you can not understand that. -- Jim Pennino |
Dipoles, why height matters
Jerry Stuckle wrote:
On 11/21/2014 8:22 PM, wrote: Jerry Stuckle wrote: On 11/21/2014 5:22 PM, Wayne wrote: snip Along the lines of a "testimonial"... I once lived in the center of a state that had an active 75 meter net. At one point I was asked to be one of the net control stations because of my consistent strong signals within the net. The secret? A 75 meter dipole at 20 feet with 100 watts. On longer paths, of course, the "big boys" kicked my butt big time. Gee, according to jimp, your antenna should have "sucked". Which shows you are incapapble of understanding the difference between NVIS propagation and skywave propagation or anything else that I wrote. Nope, I understand them a lot better than you do. And his comments had NOTHING to do with what you said. According to you, his antenna "sucked". Period. No qualification. My god you are delusional when you are raging. If you did understand it, you would know that what he said is TOTALLY consistant with what I wrote. And once again you are trying to weasel out of what you said. Just like a troll. My god you are delusional when you are raging. -- Jim Pennino |
Dipoles, why height matters
"Ian Jackson" wrote in message ... In message , Wayne writes wrote in message ... For those that do not have a firm understanding of what the chart of dipole height over ground shows, I offer the following explanation. The charts show, for a dipole antenna at various heights in wavelengths over perfect, very good, average, and extremely poor ground, the gain and elevation angle of the antenna main lobe. The main lobe is where the majority of the energy is radiated. To understand what the charts mean in the real world, first you have to understand a little bit about propagation of RF. For a dipole antenna, there are two modes of propagation that are relevant, and those are NVIS (Near Vertical Incidence Skywave) and skywave which is sometimes called skip. Both modes depend on the RF being reflected or refracted back toward Earth by the ionosphere. For NVIS mode, the RF is directed straight up, that is an elevation angle close to 90 degrees is desired. The range of NVIS communications is on the order of 50 - 650 km, depending on the state of the ionosphere. The amateur bands where this is effective is limited primarily to the 160M to 40M band, again depending on the state of the ionosphere. It is not impossible to have NVIS communications on the higher bands, just much less probable to happen. For skywave mode, a low elevation mode is desired. Most of the literature recommends angles of 30 degees or less. In this mode the RF "bounces" at more obtuse angles, and with good conditions in the ionosphere, more than once, providing communication over global distances. Skywave depends heavily on the condition of the ionosphere and during sunspot peaks often occurs well past 10M. Now since a dipole with a main lobe at 90 degrees still has some gain at low angles, though it can be 20 to 60 dB down from the main lobe, when conditions are very good some stations can still be heard by skywave mode, though it is a rarity and can not be depended on. Conversely a dipole with a low elevation angle of the main lobe has some gain at very high angles and can occasionly hear stations by NVIS mode, but again it is a rarity. The bottom line of all this is that if you desire NVIS communications, you should mount your dipole at a height where the elevation angle is close to 90 degrees while if you desire long distance communications you should mount your dipole at a height where the elevation angle is less than 30 degrees, or higher if possible. If the required height is impractical at your location, then the alternative is a ground mounted vertical or a close to ground mounted ground plane antenna, which will have an elevation angle in the 20 degree range. Along the lines of a "testimonial"... I once lived in the center of a state that had an active 75 meter net. At one point I was asked to be one of the net control stations because of my consistent strong signals within the net. The secret? A 75 meter dipole at 20 feet with 100 watts. On longer paths, of course, the "big boys" kicked my butt big time. # 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! A 20 foot high 75 meter dipole wouldn't be my first choice for an antenna. At the time, that was the highest supports I had available. I just dusted off EZNEC and out of curiosity ran the plot for a 75 meter dipole at 20 feet over "real" ground. The max lobe was 9.36 dbi straight up at 90 degrees and a 3 db down beamwidth of 99.4 degrees. The 3 db down points were at 40.3 degrees and 139.7 degrees. So at least according to EZNEC, and my own personal experience for short range HF communication on 75 meters, a low dipole is a pretty good choice. |
Dipoles, why height matters
On 11/21/2014 8:56 PM, wrote:
Jerry Stuckle wrote: On 11/21/2014 8:19 PM, wrote: Jerry Stuckle wrote: snip I've also run dipoles - I got WAS on 75 meters from Iowa with an inverted VEE running from 50' to near ground. And I had a strong signal on the Iowa 75M SSB net. I have lots of strong signal reports from around the country on 6M AM running 3W into a 2 foot collapsible whip. Of course it was at the height of sunspot cycle 19 and says NOTHING about the effectiveness of the antenna. Which has absolutely nothing to do with your comment about a dipole on 75 meters. But you're too stoopid to understand that. But it has EVERYTHING to do with your comment about WAS. But you are so enraged about being correct you can not understand that. Nope. It has NOTHING to do with a dipole on 75 meters - which is the subject of this thread. You're just trying to derail the conversation so you don't have to admit you're wrong. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Dipoles, why height matters
On 11/21/2014 8:58 PM, wrote:
Jerry Stuckle wrote: On 11/21/2014 8:22 PM, wrote: Jerry Stuckle wrote: On 11/21/2014 5:22 PM, Wayne wrote: snip Along the lines of a "testimonial"... I once lived in the center of a state that had an active 75 meter net. At one point I was asked to be one of the net control stations because of my consistent strong signals within the net. The secret? A 75 meter dipole at 20 feet with 100 watts. On longer paths, of course, the "big boys" kicked my butt big time. Gee, according to jimp, your antenna should have "sucked". Which shows you are incapapble of understanding the difference between NVIS propagation and skywave propagation or anything else that I wrote. Nope, I understand them a lot better than you do. And his comments had NOTHING to do with what you said. According to you, his antenna "sucked". Period. No qualification. My god you are delusional when you are raging. Read your own words. YOU said it - not me. If you did understand it, you would know that what he said is TOTALLY consistant with what I wrote. And once again you are trying to weasel out of what you said. Just like a troll. My god you are delusional when you are raging. Once again you refuse to discuss the topic. Instead of admitting you are wrong, you are making ad hominim attacks. How like a troll. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
Dipoles, why height matters
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'). -- Ian |
Dipoles, why height matters
El 22-11-14 3:01, Wayne escribió:
"Ian Jackson" wrote in message ... In message , Wayne writes wrote in message ... For those that do not have a firm understanding of what the chart of dipole height over ground shows, I offer the following explanation. The charts show, for a dipole antenna at various heights in wavelengths over perfect, very good, average, and extremely poor ground, the gain and elevation angle of the antenna main lobe. The main lobe is where the majority of the energy is radiated. To understand what the charts mean in the real world, first you have to understand a little bit about propagation of RF. For a dipole antenna, there are two modes of propagation that are relevant, and those are NVIS (Near Vertical Incidence Skywave) and skywave which is sometimes called skip. Both modes depend on the RF being reflected or refracted back toward Earth by the ionosphere. For NVIS mode, the RF is directed straight up, that is an elevation angle close to 90 degrees is desired. The range of NVIS communications is on the order of 50 - 650 km, depending on the state of the ionosphere. The amateur bands where this is effective is limited primarily to the 160M to 40M band, again depending on the state of the ionosphere. It is not impossible to have NVIS communications on the higher bands, just much less probable to happen. For skywave mode, a low elevation mode is desired. Most of the literature recommends angles of 30 degees or less. In this mode the RF "bounces" at more obtuse angles, and with good conditions in the ionosphere, more than once, providing communication over global distances. Skywave depends heavily on the condition of the ionosphere and during sunspot peaks often occurs well past 10M. Now since a dipole with a main lobe at 90 degrees still has some gain at low angles, though it can be 20 to 60 dB down from the main lobe, when conditions are very good some stations can still be heard by skywave mode, though it is a rarity and can not be depended on. Conversely a dipole with a low elevation angle of the main lobe has some gain at very high angles and can occasionly hear stations by NVIS mode, but again it is a rarity. The bottom line of all this is that if you desire NVIS communications, you should mount your dipole at a height where the elevation angle is close to 90 degrees while if you desire long distance communications you should mount your dipole at a height where the elevation angle is less than 30 degrees, or higher if possible. If the required height is impractical at your location, then the alternative is a ground mounted vertical or a close to ground mounted ground plane antenna, which will have an elevation angle in the 20 degree range. Along the lines of a "testimonial"... I once lived in the center of a state that had an active 75 meter net. At one point I was asked to be one of the net control stations because of my consistent strong signals within the net. The secret? A 75 meter dipole at 20 feet with 100 watts. On longer paths, of course, the "big boys" kicked my butt big time. # 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! A 20 foot high 75 meter dipole wouldn't be my first choice for an antenna. At the time, that was the highest supports I had available. I just dusted off EZNEC and out of curiosity ran the plot for a 75 meter dipole at 20 feet over "real" ground. The max lobe was 9.36 dbi straight up at 90 degrees and a 3 db down beamwidth of 99.4 degrees. The 3 db down points were at 40.3 degrees and 139.7 degrees. Maybe you confused directivity (D) with gain (G), or used a wrong simulation paramater. A 20' high half wave dipole for 75m over average soil has about D = 9 dBi. However because of the heat dissipation into the soil below the antenna, the actual gain will be around 3 dBi. In other words about 75% of the RF energy is dissipated into the ground. Is this problem? frequently not, as the link budget on 75/80m has lots of margin under average conditions. Only onder worse conditions (large D-layer absorption and/or high local noise level at the target location) the one with the highest EIRP (=gain*power) will make the QSO. Several years during JOTA we had a better then average NVIS antenna for 80 m (with elevated reflection wires and a well fertilized production field). With 100W input we get complaints about why we were using a PA (we don't have one!). We decided to use a QRP TRX (10W) so the FT101ZD could be used for 40 m. We had no complaints about the signal. So on average there is nothing wrong when using an NVIS antenna with say 6 dB less performance (compared to an optimized one). Nowadays we use a "downgraded version". about 3..4 dB loss of gain, but it can be installed within 20% of the time required for the big one. So at least according to EZNEC, and my own personal experience for short range HF communication on 75 meters, a low dipole is a pretty good choice. -- Wim PA3DJS Please remove abc first in case of PM |
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 |
Dipoles, why height matters
Jerry Stuckle wrote:
On 11/21/2014 8:56 PM, wrote: Jerry Stuckle wrote: On 11/21/2014 8:19 PM, wrote: Jerry Stuckle wrote: snip I've also run dipoles - I got WAS on 75 meters from Iowa with an inverted VEE running from 50' to near ground. And I had a strong signal on the Iowa 75M SSB net. I have lots of strong signal reports from around the country on 6M AM running 3W into a 2 foot collapsible whip. Of course it was at the height of sunspot cycle 19 and says NOTHING about the effectiveness of the antenna. Which has absolutely nothing to do with your comment about a dipole on 75 meters. But you're too stoopid to understand that. But it has EVERYTHING to do with your comment about WAS. But you are so enraged about being correct you can not understand that. Nope. It has NOTHING to do with a dipole on 75 meters - which is the subject of this thread. You're just trying to derail the conversation so you don't have to admit you're wrong. Strawman arguement in an attempt to deflect the arguement from your WAS statements. -- Jim Pennino |
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