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About verticals
How less efficient is a short vertical than a 1/4 vertical?
I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. Assume a source at the base. The type of source is your choice. EZNEC defaults to one amp, but can be changed to a constant power of your choice. I'm sure I've left out additional requirements, but maybe this will be a healthy discussion even so. Suggestions are welcome. |
About verticals
On 10/4/2015 10:05 AM, John S wrote:
How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. Assume a source at the base. The type of source is your choice. EZNEC defaults to one amp, but can be changed to a constant power of your choice. I'm sure I've left out additional requirements, but maybe this will be a healthy discussion even so. Suggestions are welcome. Don't you need to define all the characteristics of the antenna? I guess an impedance specification will suffice. I don't know what electrical model EZNEC uses for the transmitter, but won't you need to deal with impedance mismatch at that point? Or does the model use a current drive with infinite impedance (or conversely a voltage drive with zero impedance)? -- Rick |
About verticals
rickman wrote:
On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. Perhaps, but the post to which you reply is barely a "1 Bottle" on the "Meths Scale". I don't think that Gareth has posted less than a "2 Bottle" grade message in the 20 years he's been abusing Usenet. -- STC // M0TEY // twitter.com/ukradioamateur |
About verticals
rickman wrote:
On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. Assume a source at the base. The type of source is your choice. EZNEC defaults to one amp, but can be changed to a constant power of your choice. I'm sure I've left out additional requirements, but maybe this will be a healthy discussion even so. Suggestions are welcome. Don't you need to define all the characteristics of the antenna? I guess an impedance specification will suffice. It doesn't work that way. You define the physical structure, including the material size and type as well as the environment and EZNEC calculates the impedance, material loss, voltages, currents, near and far fields. I don't know what electrical model EZNEC uses for the transmitter, but won't you need to deal with impedance mismatch at that point? Or does the model use a current drive with infinite impedance (or conversely a voltage drive with zero impedance)? Like all circuit analysis programs, EZNEC uses ideal sources; you select the type. The default reference impedance is 50 Ohms, but can be set to anything. Is the material some real material or lossless? What you will find is that the only loss in the ANTENNA in free space is the I^2R loss of the material. -- Jim Pennino |
About verticals
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:
How less efficient is a short vertical than a 1/4 vertical? Are you talking about radiation efficiency or total efficiency? Are you including the losses in the matching system (loading coil or antenna tuna losses) needed to match a shortened antenna? http://www.antennex.com/w4rnl/col0504/amod75.html http://www.antenna-theory.com/basics/gain.php I would like to see some numbers. http://802.11junk.com/jeffl/antennas/Monopole/index.html This is a study of what various monopoles, over a perfect ground, look like in terms of gain, impedance, efficiency etc. I should probably make a summary table, but I'm busy today. Note that the shortest antenna (0.050 wavelengths) still has 100% efficiency: http://802.11junk.com/jeffl/antennas/Monopole/monopole_0_050/slides/monopole_0_050.html That's because there are no dissipative components anywhere in the antenna system. If you shove 100 watts of RF into this ideal antenna, it will either radiate or reflect 100 watts, with no losses anywhere. Well, an antenna with a 6594:1 VSWR isn't terribly useful, but if you could find a suitable ideal matching network, it would work as well as the ideal 1/4 wave monopole. Notice that I said "ideal" as in a loss less matching network. That's not going to happen. The reason short monopoles are a problem (such as an HF antenna on a vehicle) is that the matching losses are ummm... lossy. As the antenna becomes longer, the mismatch is less, the matching network less critical, and the overall losses are less. If you look again at the various results, you'll notice that the shorter antennas have far more current going through them than the longer antennas. If there are resistances in the elements (such as in a loop antenna), the higher currents will result in higher losses for shortened antennas. This may be a consideration for your less efficient shortened vertical. It is a ground plane with 4 radials (typical). Free space. Assume a source at the base. The type of source is your choice. EZNEC defaults to one amp, but can be changed to a constant power of your choice. I'm sure I've left out additional requirements, but maybe this will be a healthy discussion even so. Suggestions are welcome. Well, I do have a suggestion. Monopole antennas are very sensitive to changes in the counterpoise, earth ground characteristics, number of radials, elevation, etc. There is no univesal monopole model that works for all frequencis, all conditions, and all applications. Usefulness of the antenna also depends on the radiation angle and ability to be matched to 50 ohms. I don't think a discussion that bounces around all these parameters is going to be very useful. Perhaps if you could provide a more specific set of conditions, we might be able to analyze the situation in realistic terms, and possibly provide recommendations and alternatives. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
About verticals
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote:
I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. I just noticed the contradiction. You can't have a grounded antenna, or a ground plane in free space, where there is no ground. Also, as Jim mentioned, ideal antennas in free space have no dissipative losses. Try again please. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
About verticals
On Sun, 4 Oct 2015 12:29:28 -0400, rickman wrote:
On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. That's because he IS that someone else. Check his headers! Gareth strikes again. Typical troll tactic to change user name to thwart filters. |
About verticals
"Renee" wrote in message
... On Sun, 4 Oct 2015 12:29:28 -0400, rickman wrote: On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. That's because he IS that someone else. Check his headers! Gareth strikes again. Typical troll tactic to change user name to thwart filters. You stupid boy. |
About verticals
Renee wrote:
On Sun, 4 Oct 2015 12:29:28 -0400, rickman wrote: On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. That's because he IS that someone else. Check his headers! Gareth strikes again. Typical troll tactic to change user name to thwart filters. John S is NOT Gareth as can easily be seen from the contents of his posts, i.e. they are NOT random, babbling gibberish NOR are they extended whinning about manners. -- Jim Pennino |
About verticals
Jeff Liebermann wrote:
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote: I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. I just noticed the contradiction. You can't have a grounded antenna, or a ground plane in free space, where there is no ground. Also, as Jim mentioned, ideal antennas in free space have no dissipative losses. Try again please. What do you mean you can't have a ground plane in free space? There are no ground losses in free space, but ground plane antennas, i.e. a radiator with radials, work just fine. -- Jim Pennino |
About verticals
On 10/4/2015 1:47 PM, Renee wrote:
On Sun, 4 Oct 2015 12:29:28 -0400, rickman wrote: On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. That's because he IS that someone else. Check his headers! Gareth strikes again. Typical troll tactic to change user name to thwart filters. Now you have lost it. John S is a different person and his post looks nothing like one from someone else. -- Rick |
About verticals
On 10/4/2015 1:36 PM, Jeff Liebermann wrote:
On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote: I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. I just noticed the contradiction. You can't have a grounded antenna, or a ground plane in free space, where there is no ground. Also, as Jim mentioned, ideal antennas in free space have no dissipative losses. Try again please. Why not? Is not the ground just the other terminal on the antenna connected to the radials? Ground doesn't have to be earth ground or anything else. It is just a defined reference point. -- Rick |
About verticals
On Sun, 4 Oct 2015 15:24:39 -0400, rickman wrote:
On 10/4/2015 1:36 PM, Jeff Liebermann wrote: On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote: I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. I just noticed the contradiction. You can't have a grounded antenna, or a ground plane in free space, where there is no ground. Also, as Jim mentioned, ideal antennas in free space have no dissipative losses. Try again please. Why not? Because a free space model is defined as the absence of a "real ground", "earth ground", or something sufficiently away from the rock that you're standing on so that its influence is very small on the model. That's usually measured in wavelengths. Offhand, anything at least 10 wavelengths above the nearest ground structure (ground, trees, buildings, etc) can be ignored. For VHF/UHF, that's a fairly small distance. For HF, much longer. Is not the ground just the other terminal on the antenna connected to the radials? Nope. Which radials? The radials in a common "ground plane" antenna are certainly not considered an "earth ground". However, the buried counterpoise that forms the other half of a monopole antenna is certainly an earth ground. Note that I would need an NEC4 runtime to model a below ground radial counterpoise system. Ground doesn't have to be earth ground or anything else. It is just a defined reference point. I think the problem is too many definitions of ground here. In my world, "earth ground" means just that. It's the rock you're standing on. A "grounded" antenna, is one that uses the earth as the counterpoise. A "safety or lightning ground" is a path for atmospheric electricity and does not usually enter in the calculations. Maybe some examples might help. 1. I want to model a UHF (440 MHz) vertical "ground plane" antenna mounted on a pole on my roof. The roof is 20ft high and the antenna is mounted on top of a 10ft pole. How high above "ground" do I make my antenna model? 2. Same antenna, but with a #12 solid ground wire running to a ground rod pounded into the ground. How high above "ground" do I make my antenna model? 3. Assuming the pole is made from fiberglass, and RF power amp is mounted at the antenna (common for cellular TMA installs), will a free space model work? 4. If the 10ft pole it transplanted to the ISS, is there an "earth ground" and how high? Scroll down for my answers. Looks like I'll be busy for a few days, so I might as well answer my own questions now: 1. 10 ft. At UHF, the house is considered part of the earth ground especially if the roof is corrugated steel or full of chicken wire. Same with any LARGE mounting structure (in terms of wavelengths). 2. 10 ft. The ground wire is presumably not part of the radiating parts of the antenna and can be ignored if shielded by the ground plane wires. If long enough, it looks more like an RF choke (inductor) than an antenna element. 3. Yes, free space will work, although nearby metal structures and wires need to be considered if they can be "seen" by the radiating elements. 4. Toss a coin and 10 ft. The ISS is large enough (in terms of wavelengths at UHF) to be considered a perfect ground, as in my monopole examples. However, if you need an accurate model, the ISS has enough complex shapes that can re-radiate RF, and should probably be modeled as part of the antenna system, in free space and without any influence from the planetary rock. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
About verticals
Jeff Liebermann wrote:
On Sun, 4 Oct 2015 18:56:18 -0000, wrote: Jeff Liebermann wrote: On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote: I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. I just noticed the contradiction. You can't have a grounded antenna, or a ground plane in free space, where there is no ground. Also, as Jim mentioned, ideal antennas in free space have no dissipative losses. Try again please. What do you mean you can't have a ground plane in free space? There are no ground losses in free space, but ground plane antennas, i.e. a radiator with radials, work just fine. I'll stand my ground and defend my assertions on good grounds. Permit me to explain from the ground up. If you mount a monopole on the ISS, the NEC model would probably use the space station surface as a ground. That's not exactly what I would call "free space" because it costs so much to get into space, but that doesn't enter into the calculations. The space station would form a suitable ground plane where its presence in outer space is an incidental coincidence. However, that's not the same as an "earth ground", which is what I mean by a "real ground". Also, If I fire up 4NEC2, and setup the antenna in free space, the various grounding options become grayed out. That would suggest that there ain't no such thing as a ground or "earth ground" in expensive, errr... free outer space. Of course, I could design what is commonly called a "ground plane antenna", which would rhetorically have a "ground plane". However, that's not the same as an "earth ground". For example, if you actually model a "ground plane antenna" over an earth ground, you might end up with two grounds, which make little sense. Also, adjusting the height above ground in a "ground plane antenna" make equally little sense. The radials that form a "ground plane" should be renamed to something more definitive, such as a conical counterpoise or conical grounded sleeve antenna. Don't know about 4NEC2, but EZNEC has no problem with a ground plane antenna in free space. The ground plane in a ground plane antenna usually refers to the radial elements attached to the bottom end of the radiator, so I don't see any problem with such a configuration. Now whether or not a ground plane antenna is a usefull design to use in space is a separate issue. But what is interesting is to model a ground plane over real ground and step the height above real ground and observe what happens to the pattern as the height goes from zero to a couple of wave lengths. While getting a 40M ground plane up a half wave length would be a challenge, at 12M and above it is not, and at 6M, most ARE mounted at about 1 wavelength. Ummm... how do I model coffee grounds or has this discussion ground to a halt? Depends on whether or not I have intrigued you enough to grind the numbers for a ground plane at various heights. -- Jim Pennino |
About verticals
Jeff Liebermann wrote:
Maybe some examples might help. 1. I want to model a UHF (440 MHz) vertical "ground plane" antenna mounted on a pole on my roof. The roof is 20ft high and the antenna is mounted on top of a 10ft pole. How high above "ground" do I make my antenna model? About 30 feet, i.e. the height of the radials. 2. Same antenna, but with a #12 solid ground wire running to a ground rod pounded into the ground. How high above "ground" do I make my antenna model? For the same antenna, the same height. 3. Assuming the pole is made from fiberglass, and RF power amp is mounted at the antenna (common for cellular TMA installs), will a free space model work? Depends on the actual height above the ground in wave lengths and what else is around. 4. If the 10ft pole it transplanted to the ISS, is there an "earth ground" and how high? The ground would be free space, but for accuracy you would need to model the ISS. Scroll down for my answers. Looks like I'll be busy for a few days, so I might as well answer my own questions now: 1. 10 ft. At UHF, the house is considered part of the earth ground especially if the roof is corrugated steel or full of chicken wire. Same with any LARGE mounting structure (in terms of wavelengths). My roof is all non-conductive so I can ignore it. Your milage may vary. 2. 10 ft. The ground wire is presumably not part of the radiating parts of the antenna and can be ignored if shielded by the ground plane wires. If long enough, it looks more like an RF choke (inductor) than an antenna element. Having actually modeled such, I can say that such a wire will have little to no effect on the antenna unless it happens to be about 1/4 wavelength long. 3. Yes, free space will work, although nearby metal structures and wires need to be considered if they can be "seen" by the radiating elements. We agree totally on this one. 4. Toss a coin and 10 ft. The ISS is large enough (in terms of wavelengths at UHF) to be considered a perfect ground, as in my monopole examples. However, if you need an accurate model, the ISS has enough complex shapes that can re-radiate RF, and should probably be modeled as part of the antenna system, in free space and without any influence from the planetary rock. I would think that the shape of the ISS is such that you would need to model it and take into concideration the location relative to the solar panels and their orientation. -- Jim Pennino |
About verticals
On 10/4/2015 5:08 PM, Jeff Liebermann wrote:
On Sun, 4 Oct 2015 15:24:39 -0400, rickman wrote: On 10/4/2015 1:36 PM, Jeff Liebermann wrote: On Sun, 4 Oct 2015 09:05:57 -0500, John S wrote: I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. I just noticed the contradiction. You can't have a grounded antenna, or a ground plane in free space, where there is no ground. Also, as Jim mentioned, ideal antennas in free space have no dissipative losses. Try again please. Why not? Because a free space model is defined as the absence of a "real ground", "earth ground", or something sufficiently away from the rock that you're standing on so that its influence is very small on the model. That's usually measured in wavelengths. Offhand, anything at least 10 wavelengths above the nearest ground structure (ground, trees, buildings, etc) can be ignored. For VHF/UHF, that's a fairly small distance. For HF, much longer. I don't know why you are talking about "a real ground" when the context was a ground plane antenna. "It is a ground plane with 4 radials (typical). Free space." Clearly that can exist. You said you can't have a "ground plane". The antenna has a ground plane no matter where it is. Is not the ground just the other terminal on the antenna connected to the radials? Nope. Which radials? The radials in a common "ground plane" antenna are certainly not considered an "earth ground". No one but you is talking about an "earth ground". The comment was simply about a ground plane antenna in free space. I don't think the name "ground plane antenna" requires the antenna to have any relation to an earth ground. However, the buried counterpoise that forms the other half of a monopole antenna is certainly an earth ground. Note that I would need an NEC4 runtime to model a below ground radial counterpoise system. Ground doesn't have to be earth ground or anything else. It is just a defined reference point. I think the problem is too many definitions of ground here. In my world, "earth ground" means just that. It's the rock you're standing on. A "grounded" antenna, is one that uses the earth as the counterpoise. A "safety or lightning ground" is a path for atmospheric electricity and does not usually enter in the calculations. But no one said anything about an "earth" ground except you. A "ground plane" antenna is the topic. No one else said anything about a "grounded" antenna. Have you had too much coffee today? -- Rick |
About verticals
On Sun, 4 Oct 2015 19:44:24 -0400, rickman wrote:
I don't know why you are talking about "a real ground" when the context was a ground plane antenna. "It is a ground plane with 4 radials (typical). Free space." Clearly that can exist. You said you can't have a "ground plane". The antenna has a ground plane no matter where it is. Argh. You're right. I misread the original question. Have you had too much coffee today? No. I've been stacking firewood, dragging junk around, and doing other odd jobs around the house today. When I get tired, I sit down at the computah and post wrong information and bad advice at about 1 hr intervals. Maybe I shouldn't do that. Sorry(tm). -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
About verticals
On 10/4/2015 8:53 PM, Jeff Liebermann wrote:
On Sun, 4 Oct 2015 19:44:24 -0400, rickman wrote: I don't know why you are talking about "a real ground" when the context was a ground plane antenna. "It is a ground plane with 4 radials (typical). Free space." Clearly that can exist. You said you can't have a "ground plane". The antenna has a ground plane no matter where it is. Argh. You're right. I misread the original question. Have you had too much coffee today? No. I've been stacking firewood, dragging junk around, and doing other odd jobs around the house today. When I get tired, I sit down at the computah and post wrong information and bad advice at about 1 hr intervals. Maybe I shouldn't do that. lol -- Rick |
About verticals
On Sunday, October 4, 2015 at 9:05:23 AM UTC-5, John S wrote:
How less efficient is a short vertical than a 1/4 vertical? I would like to see some numbers. It is a ground plane with 4 radials (typical). Free space. Assume a source at the base. The type of source is your choice. EZNEC defaults to one amp, but can be changed to a constant power of your choice. I'm sure I've left out additional requirements, but maybe this will be a healthy discussion even so. Suggestions are welcome. One could spit out numbers for days given all the possibilities. Too vague are the specs.. IE: you state four radials, but model in free space. So would ground losses be an issue or not? Also the height above ground in wavelength makes a large difference. Four radials at 1/2 wave up provide low ground losses, but four radials at 1/10 wave up are not so hot. Much higher ground losses. Being as all short radiators radiate nearly all power fed to them, barring any small resistive losses, the only thing left are the matching losses. And for playing "what if", a program like "vertload" could be used for getting an idea of the efficiency of the various length radiators and spit out the number of turns needed, etc.. Will give the efficiency using whatever ground number you punch in as I recall. That's what I used to use when building mobile whips. I think it also lets you adjust the whip both below and above the coil. So you can vary the location of the coil. The only problem with vertload is it's old and DOS I think, so newer OS's won't run it without a DOS BOX or whatever.. XP will run em as is.. So I can still use them on my old laptop. This box is Win7 64, and it won't run em without the DOS program, which I haven't bothered with yet. But they say it will work.. I forgot the exact name of the DOS emulator, would I'm sure google knows what and where it is. |
About verticals
On 10/4/2015 11:29 AM, rickman wrote:
On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. Sorry guys. I didn't mean to sound like someone else. I regret starting this post now. Let's just forget it. |
About verticals
On 10/5/2015 6:51 AM, John S wrote:
On 10/4/2015 11:29 AM, rickman wrote: On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. Sorry guys. I didn't mean to sound like someone else. I regret starting this post now. Let's just forget it. I was just joking... -- Rick |
About verticals
On 10/5/2015 10:55 AM, rickman wrote:
On 10/5/2015 6:51 AM, John S wrote: On 10/4/2015 11:29 AM, rickman wrote: On 10/4/2015 10:05 AM, John S wrote: How less efficient is a short vertical than a 1/4 vertical? You are starting to sound like someone else. Sorry guys. I didn't mean to sound like someone else. I regret starting this post now. Let's just forget it. I was just joking... Well, okay. I like to discuss these things in a gentlemanly manner and learn from them. I like to use EZNEC and a Smith chart to support my thoughts, opinions, findings, confusions, etc. My purpose is purely technical. I like other peoples' input because, without it, there is no constructive thinking about how to approach the problem. Your approach may be different from mine because your brain and background is different from mine. That is a good thing. If I can just view it your way, and you can view it my way, we might gain a new insight into the problem. There are several contributors here whose posts I respect and value very much. I know I can learn a lot here if only we can exclude the protagonist and his followers by ignoring the British posts. Summary: I already know that there are people here who can help me reconcile my questions and investigations regarding technical aspects of antennas, transmission lines, ATUs, and all the fodder we hams eat up. Where else can I go to get this? |
About verticals
On Mon, 5 Oct 2015 12:41:18 -0500, John S wrote:
Summary: I already know that there are people here who can help me reconcile my questions and investigations regarding technical aspects of antennas, transmission lines, ATUs, and all the fodder we hams eat up. Where else can I go to get this? https://www.reddit.com/r/amateurradio/ http://www.eham.net/ehamforum/smf/ http://lists.contesting.com/pipermail/towertalk/ http://lists.contesting.com/archives//html/Towertalk/ etc... -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
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