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#1
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Following is a posting similar to what I made on QRZ.com in reply to a guy who
was asking what kind of antenna to use out west in the mountains surrounded by tall pines. It summarizes my recent experiences with a vertical on 80 m here in central New Jersey: Often you will hear the advice "Use a vertical. You will get the low angle of radiation which you need for DX." Be very careful. Although this statement may be true, you could still be disappointed, especially if you are surrounded by trees, and being in the mountains, might have poor soil, which is necessary for good vertical performance. I speak from experience. I have been building and improving my 80 meter vertical recently, with disappointing results. It is a full size quarter wave wire vertical, hung from a rope that goes from my 72 ft tower to a tree. I have 18 radials, 60 feet long. Now that is a pretty good vertical, with no loading coils, with not very much that can be done to improve it except maybe double the number of radials. I am located in central New Jersey on sandy soil. I have used this antenna for the past several weeks, mostly checking it out on DX. In no case has the vertical beaten out the inverted vee at 60 feet. In nearly every case the antennas are virtually identical. Even on DX to VK6 during CQWW this vertical should be kicking major butt, but it is not. Ok, so a few days ago I modelled both antennas with 4NEC2, and I made sure to include the appropriate parameters in the model for my soil conditions (poor). And I overlaid both antenna patterns on the same chart. Voila! There it is, the inverted vee beats the vertical at all angles above 10 degrees, and is equal below 10 degrees. The moral of the story, be careful about making assumptions regarding antenna performance without having an A-B switch! And maybe the other lesson to be learned is how meaningful the antenna modeling programs are. So my conclusion is that even though the vertical might have the low angle pattern, the losses in the soil do not allow the advantages to be realized. Phased arrays of similar antennas over lossy soil may show the nice pattern and f/b but the absolute value of gain expected may not be realized. 73 Rick K2XT |
#2
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![]() "Rick" wrote in message ... Following is a posting similar to what I made on QRZ.com in reply to a guy who was asking what kind of antenna to use out west in the mountains surrounded by tall pines. It summarizes my recent experiences with a vertical on 80 m here in central New Jersey: Often you will hear the advice "Use a vertical. You will get the low angle of radiation which you need for DX." Be very careful. Although this statement may be true, you could still be disappointed, especially if you are surrounded by trees, and being in the mountains, might have poor soil, which is necessary for good vertical performance. I speak from experience. I have been building and improving my 80 meter vertical recently, with disappointing results. It is a full size quarter wave wire vertical, hung from a rope that goes from my 72 ft tower to a tree. I have 18 radials, 60 feet long. Now that is a pretty good vertical, with no loading coils, with not very much that can be done to improve it except maybe double the number of radials. I am located in central New Jersey on sandy soil. I have used this antenna for the past several weeks, mostly checking it out on DX. In no case has the vertical beaten out the inverted vee at 60 feet. In nearly every case the antennas are virtually identical. Even on DX to VK6 during CQWW this vertical should be kicking major butt, but it is not. Ok, so a few days ago I modelled both antennas with 4NEC2, and I made sure to include the appropriate parameters in the model for my soil conditions (poor). And I overlaid both antenna patterns on the same chart. Voila! There it is, the inverted vee beats the vertical at all angles above 10 degrees, and is equal below 10 degrees. The moral of the story, be careful about making assumptions regarding antenna performance without having an A-B switch! And maybe the other lesson to be learned is how meaningful the antenna modeling programs are. So my conclusion is that even though the vertical might have the low angle pattern, the losses in the soil do not allow the advantages to be realized. Phased arrays of similar antennas over lossy soil may show the nice pattern and f/b but the absolute value of gain expected may not be realized. 73 Rick K2XT It would be interesting to see what 4NEC does if you raise the feedpoint, and centers of the radials, about 10 feet. Tam/WB2TT |
#3
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#4
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On Nov 6, 4:27 pm, (Rick) wrote:
So my conclusion is that even though the vertical might have the low angle pattern, the losses in the soil do not allow the advantages to be realized. Phased arrays of similar antennas over lossy soil may show the nice pattern and f/b but the absolute value of gain expected may not be realized. 73 Rick K2XT I saw pretty much the same thing. If you want truly top notch performance ground mounted, you have to lay out the wire. Well, unless you are at the beach or something.. :/ I ran mostly 40m using full size verticals, and even with 32 full length radials, I saw mediocre results at best. And I'm on a high rated ground as far as conductivity. When I elevated the antenna to 36 ft at the base is when I finally saw decent performance. Of course, it's not going to be easy to run a full size elevated ground plane on 80m.. ![]() The only way you are going to see the performance you should is by coughing up more wire. ![]() But according to some I read, 60 will do the trick rather than having to do the full blown 120.. Not a whole lot of difference between the two in theory. Even elevated at 1/8 wave, a ground plane needs appx sixty radials to equal a ground plane at 1/2 wave , using four radials. And about 120 may well be needed if you really want to equal the losses of the high ground plane. Ground clutter can be another problem, although usually not huge. But, it's just another reason why I prefer an elevated vertical if at all possible. As far as the modeling, I have to adjust the programs to "very good" ground to have it equal what I see in the real world at this QTH. If they are set to default "average" ground, the verticals get shortchanged. ![]() But on the other hand, maybe that just tells me the ground here is better than average, which actually it is... :/ I'm on the gulf coast, and most of the area rates a "30" on the conductivity maps. Thats no sure thing though.. Even though the ground is decent here, I never had better than mediocre results using a ground mounted vertical with 32 full length radials. I had very good results with the 36 ft high ground plane though. Was like day and night.. MK |
#5
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![]() You are simply comparing two verticals. I don't see why you say that. One is mounted on the ground with 16 radials, the other is simply 2 pcs of wire up 60 feet, with 120 degree included angle in my example, although I can change the angle just by typing over top of the 120 I can make it anything I want. My point was, a lot of people think that if they put up a vertical, even taking care to put a good radial field under it, and they get a low angle of radiation, they have the ultimate single element DX antenna. In fact, when you take losses into consideration a simple inverted vee beats it at all angle over 10 degrees and equals it below 10 degrees. I think that is a pretty significant statement. Rick K2XT |
#6
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Rick wrote:
. . .The moral of the story, be careful about making assumptions regarding antenna performance without having an A-B switch! . . I'd like to add, use receiving signal strength for comparison. I have a friend who occasionally entertains himself by asking for comparative reports for two antennas. The differences are sometimes striking, especially if the two antennas are described as being very different. But in reality they're the same antenna. There are at least two other good reasons for using received signals for comparison. First, you can average out the effects of QSB, which can be tens of dB, and can be different or even opposite for two different antennas. And second, you can, with a step attenuator or an S-meter calibrated with a step attenuator, accurately tell just how great the difference is. If someone else truthfully reports a two S unit difference, you don't have any way to know whether it's 4 dB or 12. Roy Lewallen, W7EL |
#7
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Rick wrote:
In fact, when you take losses into consideration a simple inverted vee beats it at all angle over 10 degrees and equals it below 10 degrees. The average gain of a 1/4WL vertical monopole with ground-mounted radials is in the ballpark of 0 dB in all directions. The average gain of a horizontal 1/2WL dipole is in the ballpark of 6 dB in two directions. It is extremely difficult, if not impossible, for a vertical monopole to achieve 6 dB gain in any direction. It is extremely difficult, if not impossible, for a horizontal dipole to achieve 0 dB gain in all directions. Comparing omnidirectional antennas to directional antennas is like comparing apples and oranges. Decide which characteristics are desirable and erect whatever antenna works best for you. Hint#1: A five-element Yagi makes a lousy net control antenna. Hint#2: A monopole with 120 radials has a lousy front-to-back ratio. -- 73, Cecil http://www.w5dxp.com |
#8
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On Nov 6, 6:05 pm, (Rick) wrote:
My point was, a lot of people think that if they put up a vertical, even taking care to put a good radial field under it, and they get a low angle of radiation, they have the ultimate single element DX antenna. In fact, when you take losses into consideration a simple inverted vee beats it at all angle over 10 degrees and equals it below 10 degrees. I think that is a pretty significant statement. Rick K2XT The only thing is 16 radials is not really what I'd call a good radial field. After what I saw here, I don't even consider 32 radials as a very good radial field.. But when I elevated the antenna I did the see good DX performance. It greatly lowers the ground losses to the point just a few radials will do the job. It smoked my dipole on long paths. And as Roy says, I use mainly the receiver to check, and also I do use an A/B switch.. But I also got plenty of checks on my signal, and of course they matched the margins I saw on receive. My dipole was not at 60 ft, but at 36 ft. But to VK land the GP always beat the dipole by 4 S units. And I really doubt raising my dipole to 60 ft would have been enough to even the score. In theory, the ground losses of my GP at 36 ft with four radials should have been appx equal to a ground mount with 60 radials. This on top of the decent ground conditions. But I also have the advantage of having a clear shot at the horizon with no clutter in the way. I know the ground/space wave greatly increased when I elevated the vertical. I could work ground wave on 40m about 90-100 miles or so. Nearly half way from Houston to San Antonio. I'd be lucky to do 20 on the dipole. But another thing... And this may surprise you.. My 40m mobile antenna is better than my 36 ft high dipole at night if the path is over 800-1000 miles.. Tested it many times to make sure it wasn't a fluke. I don't know how it would fare on 80m to dx vs the dipole.. Never really tested it. I really don't work that much dx on 80m for some reason.. I'm usually working NVIS.. MK |
#9
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#10
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On Wed, 7 Nov 2007 00:51:07 -0500, "Stefan Wolfe"
wrote: A third antenna, not discussed here, would be a real 1/4 W monopole that is truely connected to earth ground and uses no radial conductive elements. Here, the monopole functions as a dipole but 1/2 of the radiation pattern exists as a mathematical image reflecting against true ground (not a good conductor of electrons like radials, merely a zero voltage reference point). This confused example attempts to pull together disparate characteristics for using ground/radials by extending the problematic metaphor of an antenna image. It takes very little effort to answer all objections raised by this confusion, but it takes very much effort to implement the solution to this confusion that is the answer = push the radials out to the radio horizon. Anyway, the confused example has no bearing on my preceding responses; the two, the vertical and the vee (as described) are poor performers below 10 degrees. 73's Richard Clark, KB7QHC |
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