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#1
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Opinions of the many individuals depend on geographic lattitude, World
population densities, what bands happen to be favourites, G5RV's and how much money there is in the bank. Let's try to remove these distracting factors. I'll put it in somewhat different "simplistic" terms. Everything else being equal, the deciding factors are geometry and trigonometry. The performance of a dipole is better at elevation angles greater than about 45 degrees and the performance of a vertical is better at lower angles. That's because the vertical and horizontal antenna types are oriented at 90 degrees to each other. At elevation angles around 45 degrees performance is about the same for both types. The ground path distance corresponding to 45 degrees depends on height of the ionospheric reflecting layers. Layer height depends on which layer, mainly E or F2, day or night, summer or winter, and the solar sunspot cycle. (None of these important factors are taken into account by antenna modelling programs. Propagation prediction programs DO take them into account but, with them, geometry is also an essential factor.) The range of distances at which vertical and horizontal antennas have similar performances in daylight is from 140 miles (E-layer) to 500 miles (F2-layer), which falls to 370 miles at night. But what decides whether a transmiiting antenna will be used or not is NOT the distance to the receiver - it is the MUF (maximum usable frequency) The MUF is geometrically-derived which increases with distance and with a decreasing elevation angle. It also changes with geographical lattitude and sun angle. With the F2-layer the MUF can increase by 3 times the vertical critical frequency Fcrit. Thus, by using a vertical low-angle antenna there are more bands and potentially more listeners available. Fcrit is the highest frequency which is reflected from a layer at vertical incidence. At higher frequencies the wave passes straight through. The MUF for high radiation angles and short distances is therefore low. It does not increase very fast as the radiation angle falls. It varies with night and day and the solar 11-year cycle. For the E-layer in summer daylight Fcrit is about 3.5 MHz. For the F2-layer in summer daylight it is about 6.5 MHz and about 5.5 MHz at night. On winter nights Fcrit for the F2-layer is about 3.5 MHz. Fcrit and high angle MUF's are subject to variation due to solar activity. But in general only the 80m and 160m bands, and sometimes 40m, are open for short distance rag-chews. This restricts the advantages of high-angle horizontal dipoles. Finally, a horizontal dipole radiates best when broadside on. Unless it is rotateable it has weaknesses in its service area. If I had to choose, I'd always choose a half-wave 80m vertical in preference to a half-wave dipole. ---- Reg. |
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#2
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On Wed, 1 Feb 2006 15:03:10 +0000 (UTC), "Reg Edwards"
wrote: [bafflegab snipped] If I had to choose, I'd always choose a half-wave 80m vertical in preference to a half-wave dipole. Me too, except that even with two acres, I can't meet the zoning setback requirements for a 135 foot tall tower. |
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#3
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Finally, a horizontal dipole radiates best when broadside on. Unless
it is rotateable it has weaknesses in its service area. If I had to choose, I'd always choose a half-wave 80m vertical in preference to a half-wave dipole. ---- Reg.[/quote] all antennas are a trade off no antenna is better than some other antenna at everything what is better can be very subjective can you make it, do you half to buy it, can you aford it, do you have room for it, half to hide it from the neighbors, how high can you put it up, any big trees handy for hanging wires must your antenna work all bands from 80 to 10 or just be great on one or two bands what band, what use, rag chew, dxing, contest, what kind of test Cal. qso party is quite diffrent from CQ wpx 80 meter 1/2 wave vert is 130 ft high how many ops can put up a 130 ft vertical in their back yard store bought ground mounted multiband verticals good ones are expensive, nearly none are close to 1/4 wave high, and a good ground system is a must always lusted after a high gain high tower vert but they now sell for about 875 dollars u.s. and my xly is not about to let me tear up her flower gardens to lay out a ground system on 75/80 out to 750 miles a 1/4 wave vert is about as good as a dummy load good in the clear, big vertical is a great dx antenna but if you are going to dx with it on 160, 80, or 40 you are going to half to also put up a receive antenna verticals are horrid receive antennas on low bands as they pick up every bit of man made qrn 20 meter ground plane feed point at 35 or 40 ft is a wonderfull dx antenna lower bands horizontal pattern of horizontal half wave dipole do not come in to play unless at least 1/2 wave above ground dipole has been the most popular amateur radio antenna for over 60 years reason easy to make, easy to put up and keep up, for most general purpose use work very well which is better dipole or vertical, is a question that has no answer best antenna is the one you have up right now mac w8znx |
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#4
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If I had to choose, I'd always choose a half-wave 80m vertical in
preference to a half-wave dipole. In general, I'd prefer the dipole on 80m. But I work mostly close in within say 600 miles on average. A dipole will smoke most verticals at those short distances. If the dipole is at least 30-40 ft off the ground, it will still be capable of dx. If I worked all dx on 80, I'd rather have the vertical, but being I don't, I prefer the dipole. Each band is different, and it always depends on what path/distance etc, I want to work as far as the preferred antenna. In general, I'd prefer the vertical on 160m. Dipole for 80 and 40, and usually 20. I've tried both a 1/4 GP and a dipole on 20m for average use, and found I prefer the dipole. Probably ditto for 17,15. But on 10m, I prefer a 1/2, 5/8 vertical if I can't have a beam. On 10m, you see quite a bit of local chatter, and most tend to run vertical if they want a decent ground/space wave. It also gives them a good dx signal. If you run a dipole on 10m, your long haul will be good, but local operation fairly poor. There really is no best type antenna except to suit the job at hand. If I'm on 40m in the day, give me me a good dipole, loop, etc . But 40m at night 800-1000 miles to the coasts? I'd rather be sitting in my truck running the mobile. No joke. It will do a better job vs my appx 40 ft tall dipole. That was tested over and over again. No fluke of the band cdx. On 40 at night, which is best will nearly always be distance determined. Look at the lowly efficiency of the mobile vs the dipole. At night, it doesn't really mean squat. What matters is that you have radiation at the angle you need to make that hop. My mobile spits more rf at the desired angle than my 40 ft high dipole does at those semi low angles despite being half crippled as far as efficiency vs a full size antenna. So polarization is nothing to ignore if you want the best bang for the buck. I bet my mobile ant sitting sideways would be pretty lame in that case. Or say take two like mobile antennas and make a short dipole. It would stink up the place on those long hauls vs the normal vertical mobile antenna. But it might be slightly better in the day working 200 miles away. The best is to have both. And use a switch to be able toquickly compare. You will see some interesting things as far as band cdx, signal fluctuations, etc over time. It really boils down to using experience working the various bands, at the various times of day, season, to know which will likely be the best at a given time. It's 1.49 in the AM here right now. If I had to get on 40m right now, give me the vertical any day. That would change in a few hours though when I started losing the long haul stuff and had it replaced by the various old farts and rednecks I work on a more local scale. :/ I'd then be on the dipole. MK |
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#6
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This is an early stage of the experiment, but
I believe that there is a lot to say with the lower noise on the horizontal antenna station Probably has a lot to do with the particular sites though. It's quite possible to be near a noise source that is mainly vertical polarized. In a case like that, it's possible it could be a problem. But I never saw the difference in noise levels you are seeing. At the worst, I might see appx 2 S units, but sometimes it might only be one, or even other times , nearly no difference at all. Most of the noise I would see at this location is power line noise. It seems to effect both horizontal and vertical nearly equally. ![]() Probably cuz much is radiated by horizontal power lines. I've never tested it, but I think if you are in a noiseless location, the difference would be fairly small as far as meter readings just measuring the average atmospheric noise. The reason I say this is because sometimes I would see little difference in noise between the two. But other times I might see more. But you could see small differences just from the increase in strength of dx signals. IE: if you had T-storms 1500 miles away, it's quite likely the vertical will receive them stronger than the horizontal due to the normal operation of the antennas. Anyway, I don't totally consider what you see as the norm. "4 s units" You probably have a local vertical noise source nearby. If it's power line, etc, you might be able to track it down and get it fixed. ![]() I'd be curious to see if you see the same 4 S unit noise difference over a period of time. Like I say, mine would vary. But noise never was much of a concern on mine. Never gave it much thought at all. Kinda weird too being I'm in a big city, in a residential area. Being mine was elevated at 36 ft at the base, I also had a pretty good line of sight to any potential noise sources. The tip of the radiator was at about 68 ft. As far as the VE being better on the wire, that's probably fairly normal, being he wasn't dx. Also, as a final note, while your butternut with 20 radials is ok, it still isn't quite up to the performance I saw with mine at 36 ft, using a full size antenna. So I saw a larger signal increase on the dx than you I bet. Mine was appx equal to a full length monopole with 60 radials, if ground mounted. I'd have to look, but my ground may be a bit better too. I'm right on the edge of being in a "30" zone. Of course, raising efficiency raises s/n equally, but I noticed that I never saw the same performance I had with the ground plane, when I ran the same full size vertical on the ground with 32 radials. That antenna was about equal to my dipoles at 1500 miles. Maybe a small bit better, but not any 2 S units worth like the GP was. So regardless of some saying the number of radials is not too important, it must be, if you want the best performance. Sure made a difference here... Either that, or elevating it above the surroundings makes the difference. Myself, I think it's about 75% the first, and 25% the second... Elevating the antenna for sure increased my local ground wave. I could work 50 miles away ground wave easy. I'd have cases in the daytime where I'd lose locals due to the band stretching out. But I could still nail them at S 9 using the GP, where the dipole would be hard to read backscatter. Of course, if the band was open short, I'd be 10-20-30 over 9 on the dipole to the same location. Anyway, I guess you gotta use what works, but I don't think it's totally normal to see a huge difference in noise between vertical and horizontal unless something local is the culprit. MK |
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#7
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My geometric argument that beyond distances of several hundred,
perhaps 500 miles, the vertical puts down a stronger signal and receives stronger signals than the horizontal dipole cannot be disputed. If you can't be heard at 1000 miles or more using a dipole, you are more likely to be heard using a vertical regardless of what antenna the other fellow is using to receive. At great distances you are much more likely to be heard using a vertical at the same average height above its surroundings. Signal to noise ratio does matter of course. Local noise level is much greater than received from distance sources for obvious reasons. Local noise is vertically polarised. It comes in via groundwave. Noise from a distance is randomly polarised. It comes in via the ionosphere. So in towns and cities, with buildings wiring, overhead power and phone lines, where most of us live, the vertical collects more local noise. In the wide open countryside both types of antenna tend to perform equally well on randomly polarised, distant noise levels. With distant noise and interference and distant signals, both types of antenna result in the same signal to noise ratio in the receiver. But the vertical antenna receives the stronger signal plus noise. If the internal receiver noise is greater than the received signal plus noise then the vertical antenna will win the contest. However, there is another effect which sometimes gives the dipole the advantage. It is multi-hop propagation. The angle of elevation of the radio path increases with the number of hops involved. The number of hops depends on the sun-angle and day or nighttime. Across the States or across the Pacific, for example, the propagation loss can be much less with 2 or 3 hops than it is with one or two hops. Waves sometimes bounce between the F2 and E layers. The increase in elevation angle favours the horizontal dipole. And how many amateurs know the number of hops involved at any point in time? But what eventually favours the vertical over the dipole is their respective service areas. The service area covered by the vertical is many times, far greater than the dipole and so is the world wide distribution of radio amateurs and short-wave listeners. We have now returned to the simplistic but precise Geometry of the ancient Egyptians and Greeks. ;o) ---- Reg, G4FGQ. |
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#8
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Reg wrote:
"If you can`t be heard at 1000 miles or more using a dipole, you are more likely to be heard using a vertical regardless of what the other fellow is using to receive." That must not always be the case. Otherwise all the shortwave broadcast stations I`ve worked in, and seen for that matter, would not use horizontal antennas. They have no way of knowing what their audience will use for antennas, and it does not make much difference as following ionospheric reflection, all wave polarizations are available and may be received. At the equator, a time zone is about 1000 miles wide. at the poles (a bad place for shortwave propagation) the width of a time zone is insignificant. All the stations I refer to are in the temperate zone and their targets are likely 1000 miles or so away, though some targets of some stations are only a few hundred miles away. Antennas at these shortwave broadcast stations are a product of studying successful antennas and carefully designing new antennas anf testing their performance in and around their intended targets. They are proved to be effective. Why would a vrtical antenna be better? From Arnold B. Bailey`s giant antenna catalog in his "TV and Other Receiving Antennas", the free-space gain is the same for a ground plane as it is for a center-fed 1/2-wave dipole. An antenna`s proximity to the earth may change the balance between horizontal and vertical antennas. Terman writes on page 886 of his 1955 edition: "Consider an antenna that is far enough from ground so that the total power radiated by a given set of antenna currents is independent of the presence of the ground. Then a ground reflection that reinforces the main lobe will double the field strength of the main lobe, and so will increase directive gain of the antenna system by a factor of 4. This condition corresponds to an antenna height great enough to make the mutual impedance between the antenna and its image small (see page 894).With horizontally polarized systems this will be the case if the center of the antenna is at least one wavelength above ground; with vertically polarized systems it is true even at lower heights. However. when the antenna is sufficiently close to the ground the effect of the ground reflection is to cause the directive gain to differ from 4. Thus , for a vertical doublet close to the ground, the directive gain is twice the free-space value, since the presence of the ground does not alter the directional pattern and there is no energy radiated in the direction of the hemisphere occupied by the ground. In contrast, the directive gain of a horizontal antenna very close to the ground can be more than 4 as compared with the same antenna in free space, as discussed below in connection with Fig. 23-36." Seems horizontal antenna users are not fools after all. Best wishes, Richard Harrison, KB5WZI |
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#9
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#10
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Mike Coslo wrote:
. . . I gotta get these two meters calibrated against each other. . . . If you don't have a signal generator with variable output, connect the two feedlines through a DPDT switch so it swaps the antenna to each receiver when you switch it back and forth. Write down the meter reading on each receiver for the same signal from the same antenna. It probably won't take long to accumulate a decent cross reference. Of course, you still won't have a clue as to how many dB each meter unit represents. That'll take an investment of a few dollars and an evening to make a step attenuator. Roy Lewallen, W7EL |
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