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OK, let's discuss dipoles vs length
The thread about a new philosophy was about 246 posts long including the
drift into mechanisms of photons and quarks. I wish to start this thread by discussing the merits of dipoles with respect to length. I really don't want to start another thread of flames. Please help me do this. Let's confine the discussion to... * It is a wire dipole (keep the wire AWG to practical values, please). * The dipole's length is variable. * It may or may not have wire resistance (state your value). * The source is placed at the center of the antenna. * There is no transmission line. * There are no matching devices. * This is a theoretical discussion but may include practical parameters. EZNEC or NEC, provides answers to these questions, I think. I will do some modeling and I'd like to compare my results to other results. Let's kick them around. Cheers, John KD5YI |
OK, let's discuss dipoles vs length
John S wrote:
The thread about a new philosophy was about 246 posts long including the drift into mechanisms of photons and quarks. I wish to start this thread by discussing the merits of dipoles with respect to length. I really don't want to start another thread of flames. Please help me do this. Let's confine the discussion to... * It is a wire dipole (keep the wire AWG to practical values, please). * The dipole's length is variable. * It may or may not have wire resistance (state your value). * The source is placed at the center of the antenna. * There is no transmission line. * There are no matching devices. * This is a theoretical discussion but may include practical parameters. EZNEC or NEC, provides answers to these questions, I think. I will do some modeling and I'd like to compare my results to other results. It does. Let's kick them around. There is nothing to kick around unless you want to argue about whether the various NEC implementations provide valid results. What NEC will tell you is that as the .5 wave dipole gets shorter and shorter, the resistive part of the antenna impedance decreases and the capacitive part increases and the patern and maximum gain changes very slightly. As the ratio of resistive input impedance to the wire resistance get smaller, the I^2R losses increase. But don't let that stop you from doing it. People often learn much better from actual doing then they do from lectures. BTW, you have to pay some attention to segmentation and as you get smaller and smaller the segmentation limits just how accurate the simulation is. -- Jim Pennino |
OK, let's discuss dipoles vs length
On 10/10/2014 1:15 PM, John S wrote:
The thread about a new philosophy was about 246 posts long including the drift into mechanisms of photons and quarks. I wish to start this thread by discussing the merits of dipoles with respect to length. I really don't want to start another thread of flames. Please help me do this. Let's confine the discussion to... * It is a wire dipole (keep the wire AWG to practical values, please). * The dipole's length is variable. * It may or may not have wire resistance (state your value). * The source is placed at the center of the antenna. * There is no transmission line. * There are no matching devices. * This is a theoretical discussion but may include practical parameters. EZNEC or NEC, provides answers to these questions, I think. I will do some modeling and I'd like to compare my results to other results. Let's kick them around. Cheers, John KD5YI I forgot to add to the second * item, that we could use .5 wavelengths, ..25 wavelengths, .1 wavelengths and .05 wavelengths for comparison purposes. |
OK, let's discuss dipoles vs length
* It is a wire dipole (keep the wire AWG to practical values, please).
* The dipole's length is variable. I forgot to add to the second * item, that we could use .5 wavelengths, .25 wavelengths, .1 wavelengths and .05 wavelengths for comparison purposes. In many of the antenna discussions I've read, the term "dipole" is often reserved for antennas which are of approximately half-wavelength resonance at the frequency in question. "Doublet" is used for a center-fed dipole-like antenna of other lengths... for example, a 40-meter dipole which is actually being used on 15 meters would be referred to as a doublet. In this sort of terminology, one could consider a "dipole" to be a particular special case of a "doublet". Of course, there's the other school of thought which calls *all* of these antennas "dipoles" (e.g. a "short dipole" or a "5/4-wave center-fed dipole". |
OK, let's discuss dipoles vs length
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OK, let's discuss dipoles vs length
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OK, let's discuss dipoles vs length
"John S" wrote in message
... No. I do not want to argue. If you do not want to participate, please feel free to not post in this thread. I'm sure that your knowledge will be gratefully accepted when you post if you can do so in a gentlemanly manner. A great pity that you did not apply the same to yourself when contributing to my thread about the medium. |
OK, let's discuss dipoles vs length
John S wrote:
On 10/10/2014 1:50 PM, wrote: John S wrote: The thread about a new philosophy was about 246 posts long including the drift into mechanisms of photons and quarks. I wish to start this thread by discussing the merits of dipoles with respect to length. I really don't want to start another thread of flames. Please help me do this. Let's confine the discussion to... * It is a wire dipole (keep the wire AWG to practical values, please). * The dipole's length is variable. * It may or may not have wire resistance (state your value). * The source is placed at the center of the antenna. * There is no transmission line. * There are no matching devices. * This is a theoretical discussion but may include practical parameters. EZNEC or NEC, provides answers to these questions, I think. I will do some modeling and I'd like to compare my results to other results. It does. Let's kick them around. There is nothing to kick around unless you want to argue about whether the various NEC implementations provide valid results. No. I do not want to argue. If you do not want to participate, please feel free to not post in this thread. I'm sure that your knowledge will be gratefully accepted when you post if you can do so in a gentlemanly manner. A bit sensitive, are we? What NEC will tell you is that as the .5 wave dipole gets shorter and shorter, the resistive part of the antenna impedance decreases and the capacitive part increases and the patern and maximum gain changes very slightly. Not concerned about the pattern. You should at least be concerned about the maximum gain if for no other reason than to address claims that very short antennas "do not perform". As the ratio of resistive input impedance to the wire resistance get smaller, the I^2R losses increase. Yes, of course. Which changes faster? I can't say as I have never plotted the data but it would be informative if you were to do so if you are going to do this. I would think a plot of I^2R loss versus length in wavelength for at least two different wire sizes would be instructive, e.g. #8 and #18. But don't let that stop you from doing it. I have never let other people's opinions stopped me from exploring and learning. People often learn much better from actual doing then they do from lectures. True. Today, however, it is nice to be able to explore so many configurations without spending a lifetime of climbing trees or erecting support poles or installing towers, or.... Yes, simulations prevent a lot of wasted effort. I once got a hare brained idea for an antenna and modeled it first. It turned out to be easy to construct with good gain, but an input impedance in the order of an Ohm and impractical to feed. Oh well... BTW, you have to pay some attention to segmentation and as you get smaller and smaller the segmentation limits just how accurate the simulation is. I know how that is done. Is this information for me or the other readers? For whoever is not aware that such limitations exist. -- Jim Pennino |
OK, let's discuss dipoles vs length
David Platt wrote:
* It is a wire dipole (keep the wire AWG to practical values, please). * The dipole's length is variable. I forgot to add to the second * item, that we could use .5 wavelengths, .25 wavelengths, .1 wavelengths and .05 wavelengths for comparison purposes. In many of the antenna discussions I've read, the term "dipole" is often reserved for antennas which are of approximately half-wavelength resonance at the frequency in question. That is the amateur radio convention, but not so for a physicist. When a physicist is talking about 1/2 wave dipoles it is either stated explicitly or obvious from the context. "Doublet" is used for a center-fed dipole-like antenna of other lengths... for example, a 40-meter dipole which is actually being used on 15 meters would be referred to as a doublet. In this sort of terminology, one could consider a "dipole" to be a particular special case of a "doublet". Again, this is amateur radio convention. I don't think I have ever seen the term doublet in a "science" publication. Of course, there's the other school of thought which calls *all* of these antennas "dipoles" (e.g. a "short dipole" or a "5/4-wave center-fed dipole". Yep, like you find in physics books, which BTW will always be center fed unless otherwise specified. All this language stuff becomes important if you concider the reading audience can consist of anyone from someone with a passing interest and little education to a Sheldon Cooper theoretical physicist. -- Jim Pennino |
OK, let's discuss dipoles vs length
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OK, let's discuss dipoles vs length
On Fri, 10 Oct 2014 20:08:51 -0000, wrote:
(...) This group is the only one that I read where topic drift ocurrs almost immediately, often on the first or second followup posting. In other groups, it usually takes 5 to 7 messages in a thread to produce the same result. The problem is that everyone (including me) tends to post about things that they are familiar with, know something about, or are passionate about the topic (even if they know nothing about it). If the initial question or request for comments does not fit these criteria, many people will simply warp the discussion until it does. For example, I know something about the mecahanics of antennas, something about using NEC models, and have a fair collection of anecdotes and photos from my days in the 2way radio biz. However, this thread is allegedly about antenna theory, where I am seriously lacking. Since I don't want to twist the topic away from theory and into reality, I haven't said anything worth reading (including this rant). On the contrary, I think it is quite a worthwile effort especially if you summarize and publish the results for the benefit of all the arm wavers saying things like "short antennas are poor radiators". Good idea. I'm curious, but not curious enough to dig through several hundred off topic comments to excavate relevent information. Then you can discuss real data instead of arguing about what some naif pulled out of his ass. "Data is free. Information must be fought for" (Former statistics instructor in college about 1968). Speaking of dipole antennas, I did this study a while back: http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html Animated version: http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html It's a 1/2 wave dipole at various heights above a real ground. Any semblance to textbook dipole pattern is long gone. I also did a study of monopoles of various lengths above a ground. There are a few that are less than 1/4 wave long which should help with some short antenna phenomenon. http://802.11junk.com/jeffl/antennas/Monopole/index.html Length Gain wl dBi 0.050 4.75 0.125 4.85 0.250 5.19 0.500 6.96 0.625 8.01 Notice that the gain doesn't really drop very much when the monopole is shorter than 1/4 wavelength long. A 1/2 wave dipole exhibits a similar lack of gain loss for short antennas. So, why are short antennas generally frowned upon? Lots of reasons but the big one are losses in the matching networks. the 0.050 wavelength antenna looks like about 700 ohms impedance. The 0.125 antenna is about -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
OK, let's discuss dipoles vs length
On 10/10/2014 3:08 PM, wrote:
John S wrote: On 10/10/2014 1:50 PM, wrote: John S wrote: The thread about a new philosophy was about 246 posts long including the drift into mechanisms of photons and quarks. I wish to start this thread by discussing the merits of dipoles with respect to length. I really don't want to start another thread of flames. Please help me do this. Let's confine the discussion to... * It is a wire dipole (keep the wire AWG to practical values, please). * The dipole's length is variable. * It may or may not have wire resistance (state your value). * The source is placed at the center of the antenna. * There is no transmission line. * There are no matching devices. * This is a theoretical discussion but may include practical parameters. EZNEC or NEC, provides answers to these questions, I think. I will do some modeling and I'd like to compare my results to other results. It does. Let's kick them around. There is nothing to kick around unless you want to argue about whether the various NEC implementations provide valid results. What NEC will tell you is that as the .5 wave dipole gets shorter and shorter, the resistive part of the antenna impedance decreases and the capacitive part increases and the patern and maximum gain changes very slightly. As the ratio of resistive input impedance to the wire resistance get smaller, the I^2R losses increase. But don't let that stop you from doing it. People often learn much better from actual doing then they do from lectures. BTW, you have to pay some attention to segmentation and as you get smaller and smaller the segmentation limits just how accurate the simulation is. Ok, I guess I had hoped to have a good conversation concerning the subject. Jim has convinced me that it is not a worthwhile effort. Cheers. On the contrary, I think it is quite a worthwile effort especially if you summarize and publish the results for the benefit of all the arm wavers saying things like "short antennas are poor radiators". Then you can discuss real data instead of arguing about what some naif pulled out of his ass. |
OK, let's discuss dipoles vs length
On 10/10/2014 3:08 PM, wrote:
John S wrote: On 10/10/2014 1:50 PM, wrote: John S wrote: The thread about a new philosophy was about 246 posts long including the drift into mechanisms of photons and quarks. I wish to start this thread by discussing the merits of dipoles with respect to length. I really don't want to start another thread of flames. Please help me do this. Let's confine the discussion to... * It is a wire dipole (keep the wire AWG to practical values, please). * The dipole's length is variable. * It may or may not have wire resistance (state your value). * The source is placed at the center of the antenna. * There is no transmission line. * There are no matching devices. * This is a theoretical discussion but may include practical parameters. EZNEC or NEC, provides answers to these questions, I think. I will do some modeling and I'd like to compare my results to other results. It does. Let's kick them around. There is nothing to kick around unless you want to argue about whether the various NEC implementations provide valid results. What NEC will tell you is that as the .5 wave dipole gets shorter and shorter, the resistive part of the antenna impedance decreases and the capacitive part increases and the patern and maximum gain changes very slightly. As the ratio of resistive input impedance to the wire resistance get smaller, the I^2R losses increase. But don't let that stop you from doing it. People often learn much better from actual doing then they do from lectures. BTW, you have to pay some attention to segmentation and as you get smaller and smaller the segmentation limits just how accurate the simulation is. Ok, I guess I had hoped to have a good conversation concerning the subject. Jim has convinced me that it is not a worthwhile effort. Cheers. On the contrary, I think it is quite a worthwile effort especially if you summarize and publish the results for the benefit of all the arm wavers saying things like "short antennas are poor radiators". Then you can discuss real data instead of arguing about what some naif pulled out of his ass. Apologies for the blank post. I hit the wrong button. OK, so lets analyze my results: Conditions are free space, wire is #14 gauge but may have zero ohms where noted. The antenna is a dipole with the source connected at the center, F=7MHz. I'm using EZNEC with a source of 1 watt. Antenna resonance plays no part in this. # segments = 99 unless otherwise noted. Lambda Wire Rin Gavg(dbi) Gmax(dbi) Efficiency 0.5 zero 80 0 2.16 100% 0.5 #14 73.6 -.09 2.08 98% 0.25 zero 13.2 0 1.85 100% 0.25 #14 13.7 -.17 1.69 96% 0.125 zero 3 0 1.78 100% 0.125 #14 3.25 -.33 1.45 93% 0.05 zero .464 0 1.76 100% 0.05 #14 .556 -.78 0.98 83% Rin is the terminal resistance only. Gave is the average gain integrated over the pattern, Gmax is the highest gain detected. Unless I have done something wrong, I see that a dipole that is .05 wavelengths long is within 20% of being as efficient as a half-wave dipole. Even including wire resistance. I invite discussion in any case. |
OK, let's discuss dipoles vs length
John S wrote:
snip OK, so lets analyze my results: Conditions are free space, wire is #14 gauge but may have zero ohms where noted. The antenna is a dipole with the source connected at the center, F=7MHz. I'm using EZNEC with a source of 1 watt. Antenna resonance plays no part in this. # segments = 99 unless otherwise noted. Lambda Wire Rin Gavg(dbi) Gmax(dbi) Efficiency 0.5 zero 80 0 2.16 100% 0.5 #14 73.6 -.09 2.08 98% 0.25 zero 13.2 0 1.85 100% 0.25 #14 13.7 -.17 1.69 96% 0.125 zero 3 0 1.78 100% 0.125 #14 3.25 -.33 1.45 93% 0.05 zero .464 0 1.76 100% 0.05 #14 .556 -.78 0.98 83% Rin is the terminal resistance only. Gave is the average gain integrated over the pattern, Gmax is the highest gain detected. Unless I have done something wrong, I see that a dipole that is .05 wavelengths long is within 20% of being as efficient as a half-wave dipole. Even including wire resistance. I invite discussion in any case. The diameter of #14 solid wire is 0.0641"; how about a line for #8, which is 0.1285"? -- Jim Pennino |
OK, let's discuss dipoles vs length
Jeff Liebermann wrote:
snip Speaking of dipole antennas, I did this study a while back: http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html Animated version: http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html It's a 1/2 wave dipole at various heights above a real ground. Any semblance to textbook dipole pattern is long gone. Yep, ground has a huge effect on some types of antennas. An instructive slide show would be the vertical pattern of a horizontal 1/2 dipole at .1, .2, ... .5 wavelengths over ground. Another one would be a 3 element beam at those heights. I also did a study of monopoles of various lengths above a ground. There are a few that are less than 1/4 wave long which should help with some short antenna phenomenon. http://802.11junk.com/jeffl/antennas/Monopole/index.html Length Gain wl dBi 0.050 4.75 0.125 4.85 0.250 5.19 0.500 6.96 0.625 8.01 Notice that the gain doesn't really drop very much when the monopole is shorter than 1/4 wavelength long. A 1/2 wave dipole exhibits a similar lack of gain loss for short antennas. So, why are short antennas generally frowned upon? Lots of reasons but the big one are losses in the matching networks. the 0.050 wavelength antenna looks like about 700 ohms impedance. The 0.125 antenna is about Nope, the vertical does the same thing when shortened from 1/4 as a dipole shortened from 1/2 wave. -- Jim Pennino |
OK, let's discuss dipoles vs length
On Sat, 11 Oct 2014 11:47:22 -0500, John S
wrote: Unless I have done something wrong, I see that a dipole that is .05 wavelengths long is within 20% of being as efficient as a half-wave dipole. Even including wire resistance. Sounds about right except that it doesn't include any losses introduced by the necessary matching network and real ground losses at HF frequencies. Expanding my table to include radiation efficiency: http://802.11junk.com/jeffl/antennas/Monopole/index.html Length Gain Radiation wl dBi Efficiency 0.050 4.75 99.09% 0.125 4.85 99.66% 0.250 5.19 99.93% 0.500 6.96 99.97% 0.625 8.01 99.93% In other words, there's nothing inherent in the length of the radiator that would affect radiation efficiency. If there is a drop in radiation efficiency, then it's mostly due to ground losses, material losses I2R, and matching losses). I invite discussion in any case. NEC: Power Efficiency vs. Radiation Efficiency L. B. Cebik, W4RNL http://www.antennex.com/w4rnl/col0504/amod75.html Lots of examples of how "efficiency" calculations work, and how various common antenna configurations affect the results. (I need to re-read the article as there's plenty about this which I don't understand very well). Test cases 5 and 6 are short monopoles, which should have something to do with short dipoles. From the bottom of the page: "Unlike the vertical monopole, the horizontal dipole shows much more regular changes of radiation efficiency with changes of soil type, ranging from 80.01% over very good soil to 65.93% over very poor soil." -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
OK, let's discuss dipoles vs length
Jeff Liebermann wrote:
On Sat, 11 Oct 2014 11:47:22 -0500, John S wrote: Unless I have done something wrong, I see that a dipole that is .05 wavelengths long is within 20% of being as efficient as a half-wave dipole. Even including wire resistance. Sounds about right except that it doesn't include any losses introduced by the necessary matching network and real ground losses at HF frequencies. Expanding my table to include radiation efficiency: There is no feed because it is the ANTENNA that is being analyzed, not an antenna SYSTEM. And while I don't know if the simulation included it, NEC can include the ground losses for the ANTENNA. http://802.11junk.com/jeffl/antennas/Monopole/index.html Length Gain Radiation wl dBi Efficiency 0.050 4.75 99.09% 0.125 4.85 99.66% 0.250 5.19 99.93% 0.500 6.96 99.97% 0.625 8.01 99.93% In other words, there's nothing inherent in the length of the radiator that would affect radiation efficiency. If there is a drop in radiation efficiency, then it's mostly due to ground losses, material losses I2R, and matching losses). Ground and I^2R losses of the antenna are shown by NEC. Matching losses are NOT part of the antenna. I invite discussion in any case. NEC: Power Efficiency vs. Radiation Efficiency L. B. Cebik, W4RNL http://www.antennex.com/w4rnl/col0504/amod75.html Lots of examples of how "efficiency" calculations work, and how various common antenna configurations affect the results. (I need to re-read the article as there's plenty about this which I don't understand very well). Test cases 5 and 6 are short monopoles, which should have something to do with short dipoles. From the bottom of the page: "Unlike the vertical monopole, the horizontal dipole shows much more regular changes of radiation efficiency with changes of soil type, ranging from 80.01% over very good soil to 65.93% over very poor soil." Yep, and once the issue of size versus efficieny is put to rest, it would not be a bad idea to look at the real effects of ground, both in terms of height in wavelengths and soil quality. -- Jim Pennino |
OK, let's discuss dipoles vs length
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OK, let's discuss dipoles vs length
Lostgallifreyan wrote:
wrote in : Yep, and once the issue of size versus efficieny is put to rest, it would not be a bad idea to look at the real effects of ground, both in terms of height in wavelengths and soil quality. Thankyou. This is the bit I am most weak on (though I did not grasp all the previous detail, the ground loss was an issue not lost on me, and is the one I need most to solve in my next efforts). What is this NEC program, and where can I find it? Sorry, but I have to ask, or Google will likely flood me with Nippon Electric Company details. Look at this for an overview of NEC. http://en.wikipedia.org/wiki/Numeric...magnetics_Code At the bottom under External links you will find both free and commercial implementations. EZNEC by W7EL is popular among hams and has a free demo version that is fully functional but limited in how complex a model you can generate. NEC itself just crunches and produces numbers, but there are several versions, including EZNEC, which have graphical interfaces to make it easier to build the model and view the results. I've used EZNEC+ for years. -- Jim Pennino |
OK, let's discuss dipoles vs length
"Lostgallifreyan" wrote in message me, and is the one I need most to solve in my next efforts). What is this NEC program, and where can I find it? Sorry, but I have to ask, or Google will likely flood me with Nippon Electric Company details. Start here for the explination. Near the bottom are some places to download it. There are many versions and variations by slightly differant names. Some free and some you have to buy. http://en.wikipedia.org/wiki/Numeric...magnetics_Code --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
OK, let's discuss dipoles vs length
On Sat, 11 Oct 2014 18:04:07 -0000, wrote:
Jeff Liebermann wrote: snip Speaking of dipole antennas, I did this study a while back: http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html Animated version: http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html It's a 1/2 wave dipole at various heights above a real ground. Any semblance to textbook dipole pattern is long gone. Yep, ground has a huge effect on some types of antennas. An instructive slide show would be the vertical pattern of a horizontal 1/2 dipole at .1, .2, ... .5 wavelengths over ground. Another one would be a 3 element beam at those heights. I can do both of these, but I'm busy/lazy this weekend. I also can't find the program I used to create the annimated GIF file. Argh. It would also be helpful if someone would specify the frequency range of interest. I also did a study of monopoles of various lengths above a ground. There are a few that are less than 1/4 wave long which should help with some short antenna phenomenon. http://802.11junk.com/jeffl/antennas/Monopole/index.html Length Gain wl dBi 0.050 4.75 0.125 4.85 0.250 5.19 0.500 6.96 0.625 8.01 Notice that the gain doesn't really drop very much when the monopole is shorter than 1/4 wavelength long. A 1/2 wave dipole exhibits a similar lack of gain loss for short antennas. So, why are short antennas generally frowned upon? Lots of reasons but the big one are losses in the matching networks. the 0.050 wavelength antenna looks like about 700 ohms impedance. The 0.125 antenna is about Nope, the vertical does the same thing when shortened from 1/4 as a dipole shortened from 1/2 wave. Thanks, that's what I meant to say but never finished the posting. I had to run and clicked "send" before I was finished scribbling the last paragraph. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
OK, let's discuss dipoles vs length
On Sat, 11 Oct 2014 21:49:11 -0000, wrote:
Jeff Liebermann wrote: On Sat, 11 Oct 2014 11:47:22 -0500, John S wrote: Unless I have done something wrong, I see that a dipole that is .05 wavelengths long is within 20% of being as efficient as a half-wave dipole. Even including wire resistance. Sounds about right except that it doesn't include any losses introduced by the necessary matching network and real ground losses at HF frequencies. Expanding my table to include radiation efficiency: There is no feed because it is the ANTENNA that is being analyzed, not an antenna SYSTEM. And while I don't know if the simulation included it, NEC can include the ground losses for the ANTENNA. I used a perfect ground for the monopoles. The NEC deck is shown below the charts on each page. For example: http://802.11junk.com/jeffl/antennas/Monopole/monopole_0_050/slides/monopole_0_050.html http://802.11junk.com/jeffl/antennas/Monopole/monopole_0_125/slides/monopole_0_125.html http://802.11junk.com/jeffl/antennas/Monopole/monopole_0_250/slides/monopole_0_250.html etc. Only the length of the monopole changes. Ground and I^2R losses of the antenna are shown by NEC. Matching losses are NOT part of the antenna. Agreed. I used a perfect ground and ideal conductors in my very simplistic models. The idea was to demonstrate that there is nothing inherent in the length of the antenna that would have a major effect on the gain. I threw in the other losses because I wanted to offer reasons for why short antennas are not particularly popular. It's not the antenna that's the problem. It's all the stuff that goes around the antenna (matching loss, balun loss, combiner loss, tuner loses, resistive losses, height above ground, counterpoise/ground losses, mounting structures, feed line losses, feed line radiation, etc). Yep, and once the issue of size versus efficieny is put to rest, it would not be a bad idea to look at the real effects of ground, both in terms of height in wavelengths and soil quality. Yep. I threw those into the discussion without providing anything in the model to demonstrate their effects. I could/should do that, but I'm busy/lazy this weekend. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
OK, let's discuss dipoles vs length
Jeff Liebermann wrote:
On Sat, 11 Oct 2014 18:04:07 -0000, wrote: Jeff Liebermann wrote: snip Speaking of dipole antennas, I did this study a while back: http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html Animated version: http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html It's a 1/2 wave dipole at various heights above a real ground. Any semblance to textbook dipole pattern is long gone. Yep, ground has a huge effect on some types of antennas. An instructive slide show would be the vertical pattern of a horizontal 1/2 dipole at .1, .2, ... .5 wavelengths over ground. Another one would be a 3 element beam at those heights. I can do both of these, but I'm busy/lazy this weekend. I also can't find the program I used to create the annimated GIF file. Argh. It would also be helpful if someone would specify the frequency range of interest. It doesn't matter if everything is done in wavelengths. I guess there are some who would want to see that a 160 meter dipole at say .2 wavelengths high has the same pattern as a 2 meter dipole at .2 wavelengths if for no other reason than to be assured the effects are frequency independant. -- Jim Pennino |
OK, let's discuss dipoles vs length
|
OK, let's discuss dipoles vs length
wrote in :
Look at this for an overview of NEC. http://en.wikipedia.org/wiki/Numeric...magnetics_Code At the bottom under External links you will find both free and commercial implementations. EZNEC by W7EL is popular among hams and has a free demo version that is fully functional but limited in how complex a model you can generate. NEC itself just crunches and produces numbers, but there are several versions, including EZNEC, which have graphical interfaces to make it easier to build the model and view the results. I've used EZNEC+ for years. Thanks again, I'll use that if it runs on W98. (Long story, but I decided to stay with it for too many reasons not to do so). Graphic representations will help me a lot. (There is a tool for laser beam optics that used graphical feedback of inputs to demonstrate predictions, if it's anything like that one it will be indispensible). |
OK, let's discuss dipoles vs length
"Ralph Mowery" wrote in
: "Lostgallifreyan" wrote in message me, and is the one I need most to solve in my next efforts). What is this NEC program, and where can I find it? Sorry, but I have to ask, or Google will likely flood me with Nippon Electric Company details. Start here for the explination. Near the bottom are some places to download it. There are many versions and variations by slightly differant names. Some free and some you have to buy. http://en.wikipedia.org/wiki/Numeric...magnetics_Code Thankyou. Fortunately this looks like it will be easier than finding certain versions of the CGG compiler... :) |
OK, let's discuss dipoles vs length
On 10/12/2014 6:54 AM, Lostgallifreyan wrote:
"Ralph Mowery" wrote in : "Lostgallifreyan" wrote in message me, and is the one I need most to solve in my next efforts). What is this NEC program, and where can I find it? Sorry, but I have to ask, or Google will likely flood me with Nippon Electric Company details. Start here for the explination. Near the bottom are some places to download it. There are many versions and variations by slightly differant names. Some free and some you have to buy. http://en.wikipedia.org/wiki/Numeric...magnetics_Code Thankyou. Fortunately this looks like it will be easier than finding certain versions of the CGG compiler... :) Also try EZNEC. They both use the NEC engine but EZNEC provides a different interface to the modeling. http://eznec.com/ |
OK, let's discuss dipoles vs length
John S wrote in :
Also try EZNEC. They both use the NEC engine but EZNEC provides a different interface to the modeling. Already did. :) EXNEC v5 demo. I really like the first impression I get, Runs on all Win32 (very respectable), and I like the way I can grab the 3D plot and rotate it like a SketchUp image to get a proper look at it. I mentioned a laser beam tool (called PSST) that graphically models laser cavities, hoping this EXNEC might be an antenna maker's equivalent. It is. :) It will take me a while to understand it though. |
OK, let's discuss dipoles vs length
On 10/12/2014 7:38 AM, Lostgallifreyan wrote:
John S wrote in : Also try EZNEC. They both use the NEC engine but EZNEC provides a different interface to the modeling. Already did. :) EXNEC v5 demo. I really like the first impression I get, Runs on all Win32 (very respectable), and I like the way I can grab the 3D plot and rotate it like a SketchUp image to get a proper look at it. I mentioned a laser beam tool (called PSST) that graphically models laser cavities, hoping this EXNEC might be an antenna maker's equivalent. It is. :) It will take me a while to understand it though. These are complex applications which someone with a mindset not like yours has produced. There will be a learning curve. The important thing is to not get frustrated and give up. If you need help, ask. Cheers. |
OK, let's discuss dipoles vs length
On 10/12/2014 12:41 AM, wrote:
Jeff Liebermann wrote: On Sat, 11 Oct 2014 18:04:07 -0000, wrote: Jeff Liebermann wrote: snip Speaking of dipole antennas, I did this study a while back: http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html Animated version: http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html It's a 1/2 wave dipole at various heights above a real ground. Any semblance to textbook dipole pattern is long gone. Yep, ground has a huge effect on some types of antennas. An instructive slide show would be the vertical pattern of a horizontal 1/2 dipole at .1, .2, ... .5 wavelengths over ground. Another one would be a 3 element beam at those heights. I can do both of these, but I'm busy/lazy this weekend. I also can't find the program I used to create the annimated GIF file. Argh. It would also be helpful if someone would specify the frequency range of interest. It doesn't matter if everything is done in wavelengths. I guess there are some who would want to see that a 160 meter dipole at say .2 wavelengths high has the same pattern as a 2 meter dipole at .2 wavelengths if for no other reason than to be assured the effects are frequency independant. Something else might be interesting; include the effects of sag (centenary) in a wire antenna. Has anyone done that? I mean, using EZNEC or NEC modeling. |
OK, let's discuss dipoles vs length
On 10/12/2014 10:20 AM, John S wrote:
On 10/12/2014 12:41 AM, wrote: Jeff Liebermann wrote: On Sat, 11 Oct 2014 18:04:07 -0000, wrote: Jeff Liebermann wrote: snip Speaking of dipole antennas, I did this study a while back: http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html Animated version: http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html It's a 1/2 wave dipole at various heights above a real ground. Any semblance to textbook dipole pattern is long gone. Yep, ground has a huge effect on some types of antennas. An instructive slide show would be the vertical pattern of a horizontal 1/2 dipole at .1, .2, ... .5 wavelengths over ground. Another one would be a 3 element beam at those heights. I can do both of these, but I'm busy/lazy this weekend. I also can't find the program I used to create the annimated GIF file. Argh. It would also be helpful if someone would specify the frequency range of interest. It doesn't matter if everything is done in wavelengths. I guess there are some who would want to see that a 160 meter dipole at say .2 wavelengths high has the same pattern as a 2 meter dipole at .2 wavelengths if for no other reason than to be assured the effects are frequency independant. Something else might be interesting; include the effects of sag (centenary) in a wire antenna. Has anyone done that? I mean, using EZNEC or NEC modeling. Arrgh! Catenary instead of what I posted. Damn spell checker is dumb on a lot of math and engineering terms. Sorry |
OK, let's discuss dipoles vs length
John S wrote in :
These are complex applications which someone with a mindset not like yours has produced. There will be a learning curve. The important thing is to not get frustrated and give up. If you need help, ask. Understood. Thanks. bear in mind that my mindset did manage to get to grips with phase modulation synthesis, large scale polyphony and multitimbrality, and accurate similautions of a few musical instruments, and did do alone with nothing but expired patents and service manuals, and a very few other published notes to guide me. I'm not trying to show off, my point is that while I do not give up easily, I AM alone, so my time is divided. :) If after my current break from that I go back to it, I might be listening to radio on an antenna or two while not thinking of the antennas for months. I've always been interested in this though, so I won't let it go. I'll look into NEC because the whole thing about good grounds is a particular fascination now, especially if improvising in limited or very temporary circumstances. |
OK, let's discuss dipoles vs length
John S wrote in :
Something else might be interesting; include the effects of sag (centenary) in a wire antenna. Agreed. I was thinking about that possibility last night. Meaning 'catenary', perhaps? As in 'hanging chain'? I doubt any longwire would lack this, so modelling it would be useful. |
OK, let's discuss dipoles vs length
John S wrote in :
Catenary instead of what I posted. Yes. I should have read your second post before my first reply.. |
OK, let's discuss dipoles vs length
On Sun, 12 Oct 2014 05:41:37 -0000, wrote:
Jeff Liebermann wrote: On Sat, 11 Oct 2014 18:04:07 -0000, wrote: Jeff Liebermann wrote: snip Speaking of dipole antennas, I did this study a while back: http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html Animated version: http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html It's a 1/2 wave dipole at various heights above a real ground. Any semblance to textbook dipole pattern is long gone. Yep, ground has a huge effect on some types of antennas. An instructive slide show would be the vertical pattern of a horizontal 1/2 dipole at .1, .2, ... .5 wavelengths over ground. Another one would be a 3 element beam at those heights. I can do both of these, but I'm busy/lazy this weekend. I also can't find the program I used to create the annimated GIF file. Argh. It would also be helpful if someone would specify the frequency range of interest. It doesn't matter if everything is done in wavelengths. That's why I ran the numbers at the traditional 1 meter (299.8MHz) wavelength. Everything can be easily scaled by frequency. The basic idea was to minimize the number of potential variables and effects. I was only interested in the effects caused by the length and/or height of the monopole, and didn't want to get into anything that was frequency or material dependent. I think I've successfully demonstrated that short dipoles have almost the same gain as a proper 1/2 wave dipole, if one only looks at the antenna, and ignores literally everything else. I guess there are some who would want to see that a 160 meter dipole at say .2 wavelengths high has the same pattern as a 2 meter dipole at .2 wavelengths if for no other reason than to be assured the effects are frequency independant. As long as the frequency, matching, coax cables, skin depths, ground characteristics, mounting structures, etc are the same, they'll be identical. However, when frequency, site, and construction specifics are included, such as the operating frequency, the height in meters instead of wavelength, or the use junk wire are included, the model is no longer frequency independent. Somewhere on my computah is a series of models that I built for a simple 20 meter dipole, that started with an idealized free space model, and progressed towards a real installation which by coincidence resembles my house. I threw in everything that might have an effect on the pattern to see what might happen. I got stuck at including the sloping hillside because NEC2 seems to only include a flat earth. I've also done similar studies for commercial antennas mounted on very real and quite cluttered towers. Doing these incrementally is an excellent introduction into the difference between ideal antenna patterns, as found in the literature, and the nightmarish reality of real antenna installations. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
OK, let's discuss dipoles vs length
wrote in message ... Lostgallifreyan wrote: wrote in : Yep, and once the issue of size versus efficieny is put to rest, it would not be a bad idea to look at the real effects of ground, both in terms of height in wavelengths and soil quality. Thankyou. This is the bit I am most weak on (though I did not grasp all the previous detail, the ground loss was an issue not lost on me, and is the one I need most to solve in my next efforts). What is this NEC program, and where can I find it? Sorry, but I have to ask, or Google will likely flood me with Nippon Electric Company details. # Look at this for an overview of NEC. # http://en.wikipedia.org/wiki/Numeric...magnetics_Code # At the bottom under External links you will find both free and commercial # implementations. # EZNEC by W7EL is popular among hams and has a free demo version that is # fully functional but limited in how complex a model you can generate. # NEC itself just crunches and produces numbers, but there are several # versions, including EZNEC, which have graphical interfaces to make # it easier to build the model and view the results. # I've used EZNEC+ for years. Me too. It has been extremely useful in identifying promising approaches without having to build the hardware for each. |
OK, let's discuss dipoles vs length
On 10/12/2014 11:14 AM, Lostgallifreyan wrote:
John S wrote in : These are complex applications which someone with a mindset not like yours has produced. There will be a learning curve. The important thing is to not get frustrated and give up. If you need help, ask. Understood. Thanks. bear in mind that my mindset did manage to get to grips with phase modulation synthesis, large scale polyphony and multitimbrality, and accurate similautions of a few musical instruments, and did do alone with nothing but expired patents and service manuals, and a very few other published notes to guide me. I'm not trying to show off, my point is that while I do not give up easily, I AM alone, so my time is divided. :) If after my current break from that I go back to it, I might be listening to radio on an antenna or two while not thinking of the antennas for months. I've always been interested in this though, so I won't let it go. I'll look into NEC because the whole thing about good grounds is a particular fascination now, especially if improvising in limited or very temporary circumstances. Excellent! I like to explore and I encourage everyone to do so whether it be with math tools or getting your hands dirty. Keep it up. Cheers. |
OK, let's discuss dipoles vs length
On 10/12/2014 11:19 AM, Lostgallifreyan wrote:
John S wrote in : Catenary instead of what I posted. Yes. I should have read your second post before my first reply.. No problem. Your reply was completely appropriate. We might be just a bit out of sink (he, he) sync. Let's not get too serious. |
OK, let's discuss dipoles vs length
John S wrote in :
Excellent! I like to explore and I encourage everyone to do so whether it be with math tools or getting your hands dirty. Keep it up. Indeed. :) That synth I mentioned, it took me a good chunk of lifetime waiting for someone to make so I could pay for it. I gave up waiting. :) Jeff just posted about the perils of antenna towers and hillsides vs NEC2's flat earth, and many earlier things (liek modellign with Sketchup prior to engineering in metals and plastics, have taught me caution. measure thrice, cut once. THis is how and why I want to use NEC, to save me from falling into expensive and time consuming traps, which I think it will do very well. |
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