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Vertical on a tower
I'm putting a vertical back up for transmitting and will
probably receive on my horizontal dipole. The vertical will be mounted on the top of a 30 foot Rohn 25G tower with the base grounded in cement. The question arose in my mind whether to connet the drooping elevated radials to the tower or not. To my surprise, EZNEC says that RF current flows in the tower whether the radials are connected to the tower or not. I'm using mininec ground for the simulation. The radial fields are obviously inductively coupling to the tower. Does anyone else worry about such things? -- 73, Cecil http://www.qsl.net/w5dxp |
Vertical on a tower
Cecil Moore wrote:
The question arose in my mind whether to connet the drooping elevated radials to the tower or not. To my surprise, EZNEC says that RF current flows in the tower whether the radials are connected to the tower or not. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There's no reason for the tower to be part of the antenna, so I would suggest not connecting them. Some current will flow in the tower due to close proximity induction, but don't make it worse than necessary. Hopefully the tower is not resonant on any band to avoid additional losses. Bill, W6WRT |
Vertical on a tower
Bill Turner wrote:
There's no reason for the tower to be part of the antenna, so I would suggest not connecting them. Some current will flow in the tower due to close proximity induction, but don't make it worse than necessary. Hopefully the tower is not resonant on any band to avoid additional losses. Unfortunately, the tower is close to resonance on 40m, my favorite band. Even with elevated radials at 30 feet, it is 0.8 dB down from a ground mounted vertical, according to EZNEC. Guess I'll go back to my 2x4 support system. Darn! -- 73, Cecil http://www.qsl.net/w5dxp |
Vertical on a tower
"Cecil Moore" wrote I'm putting a vertical back up for transmitting and will probably receive on my horizontal dipole. The vertical will be mounted on the top of a 30 foot Rohn 25G tower with the base grounded in cement. The question arose in my mind whether to connet the drooping elevated radials to the tower or not. To my surprise, EZNEC says that RF current flows in the tower whether the radials are connected to the tower or not. I'm using mininec ground for the simulation. The radial fields are obviously inductively coupling to the tower. Does anyone else worry about such things? ============================================ Cec, I'm curious but not surprised. What are the approximate dimensions? Height of tower. Length of vertical radiator. Number and length of radials. Any loading coils? Your discovery of current in the tower should not be surprising. It is just another radial. It seems to me there should be negligible loss in the tower. There may be a very small loss in the ground. The tower is just another radiator. There will be some effect on the radiation pattern in the vertical plane. It will affect the so-called take-off angle. It may be advantageous. Imagine what might happen if the radials were removed. ---- Reg, G4FGQ |
Vertical on a tower
Cecil Moore wrote:
Guess I'll go back to my 2x4 support system. Darn! ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 2x4s have served well for years. :-) Bill, W6WRT |
Vertical on a tower
I'm putting a vertical back up for transmitting and will
probably receive on my horizontal dipole. Why? Doesn't make sense. If the vertical is best for transmit, it should be the best for receive 98% of the time. And visa versa.. When I ran both a dipole, and a GP, I almost always transmitted on the antenna that I received the best signal to whatever path I wanted to work. If you run a good vertical for DX, and receive on the dipole you will lose half the advantage of running the vertical the way I see it. The vertical will be mounted on the top of a 30 foot Rohn 25G tower with the base grounded in cement. The question arose in my mind whether to connet the drooping elevated radials to the tower or not. Does anyone else worry about such things? I don't think it matters too much as far as the operation of the antenna. Either will work. But almost all my GP's had the radials attached to the mounting plate, which in turn was mounted to the mast. So all mine had the radials connected to the top of the mast via the mounting. Same as most any commercial ground plane... MK |
Vertical on a tower
Cecil Moore wrote:
Bill Turner wrote: There's no reason for the tower to be part of the antenna, so I would suggest not connecting them. Some current will flow in the tower due to close proximity induction, but don't make it worse than necessary. Hopefully the tower is not resonant on any band to avoid additional losses. Unfortunately, the tower is close to resonance on 40m, my favorite band. Even with elevated radials at 30 feet, it is 0.8 dB down from a ground mounted vertical, according to EZNEC. Guess I'll go back to my 2x4 support system. Darn! To fix a problem on a single band, you could de-tune the tower with a loop trap - a wire running alongside the tower for part of its height, with a capacitor to bring the whole thing to parallel resonance. It's described in the antenna books by ON4UN and G6XN (and possibly also in the ARRL Antenna Handbook). 73 from Ian GM3SEK -- 73 from Ian GM3SEK |
Vertical on a tower
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Vertical on a tower
Reg Edwards wrote:
Height of tower. Approximately 30 feet. Length of vertical radiator. 22 feet. Number and length of radials. 4 x 22 feet. Any loading coils? No, an SGC-230 at the base. Imagine what might happen if the radials were removed. I imagined that and got very high angle radiation on some bands. The tower becomes part of the radiator. -- 73, Cecil http://www.qsl.net/w5dxp |
Vertical on a tower
That's certainly not true at my QTH. The vertical has two
extra S-units of noise on receive compared to my dipole. I'm assuming the two extra S-units of noise on receive won't affect my transmitted signal. When I had my 40m vertical up, I never heard any signal that was better received on the vertical. +12 dB of noise is virtually impossible to overcome in actual practice. If you get two extra units of noise, but the signal comes up four.... Well, you get it... I didn't get much extra noise going vertical at this location. The stronger signals always overrode it. The noise should be a non issue in most cases. But this also leads to an important question. Do you actually work long haul paths? If you don't , you probably won't see much advantage to a vertical. If you listened to long haul dx paths, and the vertical never beat the dipole, you didn't have a very good vertical. Actually, I've already pondered on that in the past. Yours was pretty low, with not many radials the last time around. The combo of mediocre antenna, and not using it for long paths is why yours was never better than the dipole. If I remember right, you weren't even talking over 1000 miles most times. But almost all my GP's had the radials attached to the mounting plate, which in turn was mounted to the mast. Conductive mast? Sure. Grounded at the base too. MK |
Vertical on a tower
Nope. Verticals are notorious for picking up local man-made noise.
Man-made noise starts out with random polarization but the horizontal component is quickly "shorted out" by the earth's conductivity, leaving only the vertical polarized component. This is why AM broadcast stations universally use vertical polarization; better groundwave coverage. They are not concerned with skywave or local noise. For skywave, either one works fine, but a horizontal antenna is quieter. They don't pick up *that* much more noise. Sometimes the difference would be fairly small. When I ran both the elevated GP, and the dipole, the antenna that received best, transmitted best nearly all the time. If there were exceptions, they were so rare as not to really remember them. If you are working long haul DX paths, the signal increase of the vertical will override any extra noise. And the increase is almost always higher than the increase of noise. Noise on the vertical was never really an issue here. And I'm in the big city of Houston to boot. When I talked to VK land using both antennas, the vertical would beat the dipole by appx four S units. Both transmit and receive. If the noise came up an S unit or two, it's a non issue. When working from here to the west coast, ditto, except the difference would be two S units instead of four. Even in those cases, the noise was never high enough to make the dipole the preferred receive antenna. Dunno..I think all this "noisy on a vertical" talk is greatly overstated. Also consider that most of my local noise here is random, and often effects both antennas nearly equally. If you are working long DX and receive on a low dipole, you could be robbing yourself of a lot of received signal to be had. In my case, 4 S units worth to any long haul dx. You telling me I'm gonna see 4 S units of extra noise? Never here at this QTH... Maybe 1 or 2 at best. I *never* wanted to receive on my dipole if I was working long haul off the vertical. Would be like shooting myself in the foot. MK |
Vertical on a tower
wrote:
If you listened to long haul dx paths, and the vertical never beat the dipole, you didn't have a very good vertical. The vertical was 2 S-units noiser than the dipole. There's no evidence that, with the same height limits, a monopole vertical could ever beat a dipole's broadside performance by 12 dB at any angle. -- 73, Cecil http://www.qsl.net/w5dxp |
Vertical on a tower
wrote:
I *never* wanted to receive on my dipole if I was working long haul off the vertical. Would be like shooting myself in the foot. Sounds like your dipole was not a very good dipole. With the same height limitation, EZNEC says the vertical will NEVER be 4 S-units (24 dB) better than the dipole's broadside performance at any angle. At http://www.qsl.net/w5dxp/dipvsver.htm is a comparison of my 130 ft. dipole at 40 ft. with my 33 ft. vertical with the feedpoint at 20 ft, both on 40m. There's only a tiny sliver where the vertical beats the dipole broadside and isn't even close to 24 dB. -- 73, Cecil http://www.qsl.net/w5dxp |
Vertical on a tower
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Vertical on a tower
wrote:
Conductive mast? Sure. Grounded at the base too. I am somewhat surprised at the effect of a grounded conductive mast upon the feedpoint impedance predicted by EZNEC. On 40m, with the radials attached to the mast, the feedpoint impedance is 7.8 - j255. With the radials not attached to the mast the feedpoint impedance is 81 - j219. With no radials and using the mast as a counterpoise, the feedpoint impedance is 2044 + j1461. -- 73, Cecil http://www.qsl.net/w5dxp |
Vertical on a tower
Sounds like your dipole was not a very good dipole...
A dipole is a dipole. You can't go by what eznec says. My modeling didn't match my real world either unless I cranked the ground quality up in the modeling program. My GP was *always* about 4 s units louder than the dipole to VK. Every time I compared. I had a regular sked over there 3 times a week. The GP was always 2 S units louder to the west coast than the dipole. Every time I checked. The dipole was at 36 ft. The base of the GP was at 36 ft. There are factors in comparing the two antennas in the real world, that I don't think modeling takes full account of. Also, my ground is better than yours too. My GP was higher than your last one by nearly double. Don't confuse what you saw with your last one, with what I saw on mine. Mine was a good bit more efficient as far as radial number vs height in wavelength vs the one you ran last time. Of course, S meter readings mean zip as far as actual db improvement, but there is no doubt my GP smoked my dipole on long paths. Day and night...And the difference was reciprical xmit/rcve in almost all cases. Suit yourself, but any serious DXer will tell you there are times when one dB of S/N ratio would make the difference between QSO and no QSO Sure, but the actual signal level increase on a long path is almost always stronger than any increase in noise. I never once felt the need to use my dipole for receive in place of the GP. Would be stepping backwards. Now, on the low bands like 80/160, a beverage, etc, might be better for rcve, but I don't use those on 40m. MK |
Vertical on a tower
wrote:
The dipole was at 36 ft. The base of the GP was at 36 ft. Well, there's the problem. You stopped your dipole where your vertical started so any comparisons are bogus. Your dipole was an NVIS antenna. :-) It's not a fair comparison since the vertical was given a 2x height advantage. (That's like putting my three foot six inch grandson up against Shaquelle O'Neal in basketball. :-) Put the dipole at 70 feet, like the vertical was, and see what happens. The top of my vertical was at 53 ft. and my dipole was one of its upper guy wires at about 50 feet so the two heights were essentially opposite yours. Which brings up another question. If the top of a vertical is at a certain height, what height of dipole would be a fair comparison? It is certainly unfair to compare feedpoints at the same height, like you did. It may also be slightly unfair to compare them at the same maximum heights, like I did. It seems a fair comparison might be made when half the vertical is lower than the dipole and half is higher than the dipole, i.e. the height of the dipole is at the midpoint of the monopole? -- 73, Cecil http://www.qsl.net/w5dxp |
Vertical on a tower
Well, there's the problem. You stopped your dipole where
your vertical started so any comparisons are bogus. Bogus? How so? Your dipole was an NVIS antenna. :-) And I want it to be. It's not a fair comparison since the vertical was given a 2x height advantage. (That's like putting my three foot six inch grandson up against Shaquelle O'Neal in basketball. :-) Put the dipole at 70 feet, like the vertical was, and see what happens. I mounted both as high as they would go. I don't consider the GP as having quite twice the height advantage due to the current distribution. The top of my vertical was at 53 ft. and my dipole was one of its upper guy wires at about 50 feet so the two heights were essentially opposite yours. No , just different.. Which brings up another question. If the top of a vertical is at a certain height, what height of dipole would be a fair comparison? Dunno...But max current on the GP as at the base.. It is certainly unfair to compare feedpoints at the same height, like you did. No, it isn't. I can compare any setup I like. I'm not trying to be fair. I don't want both antennas to act the same. It may also be slightly unfair to compare them at the same maximum heights, like I did. It seems a fair comparison might be made when half the vertical is lower than the dipole and half is higher than the dipole, i.e. the height of the dipole is at the midpoint of the monopole? I don't think it matters a whole heck of a lot. I never intended for my dipole to be a dx antenna. Thats the whole purpose of putting up the GP. The dipole is for NVIS and medium range. The GP is for long range. MK |
Vertical on a tower
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Vertical on a tower
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Vertical on a tower
Cecil Moore wrote:
wrote: I'm not trying to be fair. Nuff said. I'll keep that in mind next time you say a vertical is 24 dB better than a dipole. :-) 24 db *when* for all that matter. I would note that my vertical *is* indeed about 2 S units noisier than my dipole. And some signals come in stronger, and some come in weaker. My guess is that it depends on where the signals originated from, smarter people may know the real reason. - 73 de Mike KB3EIA - |
Vertical on a tower
Nuff said. I'll keep that in mind next time you
say a vertical is 24 dB better than a dipole. :-) ........ Well, of course, I've never said any such thing. But...It is often a large noticable difference. Mike sed... My guess is that it depends on where the signals originated from Thats exactly it. In general, the farther away, the better the vertical vs the low dipole. If you don't work long haul dx, the vertical user may never see much advantage. At night on 40m, if the distance is less than 1000 miles, often the dipole and vertical would be about the same. In my case, I had to get over a 1000 miles to see much vertical advantage. At 1500 miles, it's fairly obvious. "appx 2 S units worth". In the long hauls to VK, JA, etc, often 3-4 S units worth. That will be a larger increase than your 2 s units noise increase. Modeling won't tell the whole story in a case like this. Just ask W8JI about his 300+ feet dipoles on 160m. In theory , they were supposed to beat his vertical towers. But , they usually don't on long paths where the angle is very low. I once yakked with this guy in Tokyo for a while. On the dipole at 1kw, I'd be S 8-9... On the GP with 1 kw, I'd be a solid 20 over 9. And it's reciprical as far as xmit/rcve. So I'd always be listening on the vertical if I wanted to see the same increase on my end. The only exception would be if I had something better like a beverage, etc, but that applies more to 80 and 160, than 40. Thats the real point of my comments, not which is better. To me, installing a good vertical for dx, and then listening on a low dipole to same is kinda silly being the benefits are reciprical. Also...Building a good vertical, but not using it for long hauls is kinda silly too... :/ It's the wrong tool for working 500-800 miles away. If it's never better than the dipole in that case, don't fret too much, as it's perfectly normal. MK |
Vertical on a tower
wrote:
Nuff said. I'll keep that in mind next time you say a vertical is 24 dB better than a dipole. :-) ... Well, of course, I've never said any such thing. ... Please note the smiley face. In the long hauls to VK, JA, etc, often 3-4 S units worth. Well, of course, you just said it again. :-) The standardized S-unit is 6 dB. Therefore, "4 S units" over a dipole is 24 dBd gain for your omnidirectional vertical monopole. (That's ~17 dB more gain than a three element Yagi has over a dipole.) -- 73, Cecil http://www.qsl.net/w5dxp |
Vertical on a tower
Cecil Moore wrote:
SNIPPED Well, of course, you just said it again. :-) The standardized S-unit is 6 dB. Therefore, "4 S units" over a dipole is 24 dBd gain for your omnidirectional vertical monopole. (That's ~17 dB more gain than a three element Yagi has over a dipole.) Cecil ... you are out of context [again]. The earlier post referred to long haul DX on the lower bands where a three element Yagi at optimum height is not easily within the realm of possibility for us mere mortals. [ Let's see, 1/2 wavelength high on 80 meters is 135 feet, boom length for a three element Yagi at 80 meters will approach 100 feet, You will need a football field of free space and quite a few bucks, and the approval of several engineering firms, the approval of you town building inspector, and the wrath of your neighbors to compete with a simple vertical over a decent ground.] C'mon Cecil!! Cecil ... apples and oranges ... do not enhance your reputation. Many of us use verticals on 160, 80 and 40 meters simply because they blow the pants off of horizontals on those frequencis for long haul DX. |
Vertical on a tower
Cecil, W5DXP wrote:
"I`m putting a vertical back up for transmitting and will probably receive on my horizontal dipole." If your grounded tower is near 1/4-wavelength on your favorite band, why not shunt-feed the tower and use it as your radiator? On the other hand, if you want to support another antenna and eliminate radiation from the supporting tower, outrig a wire from the tower top, hanging parallel to the tower, and connected to the tower top through an L-C network tuned to make current in the outrigged wire equal ond opposite that in the tower. The balanced currents cancel the tower`s radiation. This may be tedious for frequency hopping, but it works. Best regards, Richard Harrison, KB5WZI |
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