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Let's design a short antenna just for fun
Hi, Gentlemen -
What if we (just for fun and knowledge) design a short dipole antenna together here in the group? How short should we go as a practical matter? * What would be the worst input impedance we would would wish to deal with? That will actually determine the shortness of the dipole, yes? * There will be losses. How much are we willing to accept? This is another determining factor to the shortness, yes? * What might be the best feed arrangement for our short antenna? There are lots of ways. I don't know much about small loop antennas, but I can fade into the shadows and try to learn from you. Any other suggestions to this endeavor is also fine. Let's just discuss what we enjoy doing. If you have other topics of small antennas, let's put them on the table. Gentlemanly arguments are welcome concerning the technical aspects of our discussion. I have never had a problem with anyone who says "I believe you are wrong in this assumption and here is why." Thanks, Gentlemen. Cheers, John KD5YI |
Let's design a short antenna just for fun
On Wednesday, November 5, 2014 10:56:53 AM UTC-6, John S wrote:
Hi, Gentlemen - What if we (just for fun and knowledge) design a short dipole antenna together here in the group? How short should we go as a practical matter? * What would be the worst input impedance we would would wish to deal with? That will actually determine the shortness of the dipole, yes? * There will be losses. How much are we willing to accept? This is another determining factor to the shortness, yes? * What might be the best feed arrangement for our short antenna? There are lots of ways. I don't know much about small loop antennas, but I can fade into the shadows and try to learn from you. Any other suggestions to this endeavor is also fine. Let's just discuss what we enjoy doing. If you have other topics of small antennas, let's put them on the table. Gentlemanly arguments are welcome concerning the technical aspects of our discussion. I have never had a problem with anyone who says "I believe you are wrong in this assumption and here is why." Thanks, Gentlemen. Cheers, John KD5YI In very general terms, I would design a small dipole the same as I would design a mobile whip. Except I would have two of them back to back. The design would include all the usual considerations about loading coil location, top/end capacity hats, etc. What is good for the car, is good for the house. I have plenty of old software, much from Reg EdwardsSK, that can be used to design the antenna, determine appx losses, determine the number of turns for the loading coils, etc, etc. And then use EZNEC or whatever modeler to test the final design before going out to the garage to whip up the actual antenna. |
Let's design a short antenna just for fun
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Let's design a short antenna just for fun
John S wrote:
Hi, Gentlemen - What if we (just for fun and knowledge) design a short dipole antenna together here in the group? How short should we go as a practical matter? * What would be the worst input impedance we would would wish to deal with? That will actually determine the shortness of the dipole, yes? * There will be losses. How much are we willing to accept? This is another determining factor to the shortness, yes? * What might be the best feed arrangement for our short antenna? There are lots of ways. I don't know much about small loop antennas, but I can fade into the shadows and try to learn from you. Any other suggestions to this endeavor is also fine. Let's just discuss what we enjoy doing. If you have other topics of small antennas, let's put them on the table. Gentlemanly arguments are welcome concerning the technical aspects of our discussion. I have never had a problem with anyone who says "I believe you are wrong in this assumption and here is why." Thanks, Gentlemen. Cheers, John KD5YI I would think a dipole would be a bad candidate for a "short" antenna as you need to get the matching stuff close to the antenna to avoid I^2R losses. Some sort of ground mounted, or close to the ground, antenna might make a better choice. Also needed is some sort of definition of "short", e.g. total volume of the antenna constrained to some fraction of a wavelength. One interesting technique for shortning an antenna can be seen by lookup up US Patent 6,642,902. Essentially it is a coax in a coax with internal shorting stubs inside the coaxes with capacitive end loading. Too complex to explain in words, but the drawings in the patent are clear. -- Jim Pennino |
Let's design a short antenna just for fun
On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote:
Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. And all the other parameters can be adjusted also.. You use what you can get away with to fit the room you have. I don't recall having any mobile whips modeled, but it's hard to say as all the older designs I did are on older unused hard drives and I don't have ready access to them. I had to re-download quite a few programs due to that reason.. I change drives quite often. I just added two more 2 TB drives about a month ago.. I have several TB these days. All of Reg's old software can still be downloaded. http://zerobeat.net/G4FGQ/page3.html#S301%22 Vertload was one I used a lot for playing "what if" when designing mobile whips and other short verticals, and the info can easily be used for small dipoles. There are others programs that can be handy also. It's been a long time since I used it, but I believe vertload can be used to locate the best location on the whip to place the loading coil. In general, you want it as far out to the ends as possible for the best current distribution, but there is a point where coil losses start to outweigh the improved current distribution. So in the real world, the best location is usually appx 3/4 the way out from the feedpoint, plus or minus. And the use of capacity hats further improve current distribution, and slightly reduce the number of turns needed for the loading coil. A short dipole is never going to be quite as good as a full size version, but with proper design you can come up with quite a respectable antenna given the dinky size. John (who was KD5YI but will be N1JLS in a few weeks due to vanity) Hummm.. You now in 1 land, or you just grabbing an old call? My current call is a vanity call, which I think I've had since '96. I was WD5CJL in a past life.. I got that call in 77 when I was 20. I actually got into ham radio when I was in the eighth grade, learned the code, and even built a 6v6 transmitter from junk parts. But then I got lazy and kind of got out of it a while, and didn't actually get a ticket. Later on I got back into it, and got a ticket about six years later. I used my first 6v6 transmitter when I was a novice in 77. I was a SWL for a good while before I got into ham radio. I worked a lot of CW back in the old days. I got up to nearly 60 wpm at one point. But due to lack of activity the past several years, I can't do near that now. :( |
Let's design a short antenna just for fun
On Wednesday, November 5, 2014 1:01:02 PM UTC-6,
I would think a dipole would be a bad candidate for a "short" antenna as you need to get the matching stuff close to the antenna to avoid I^2R losses. I'd probably use small matching coils at the feed point, about the same as a mobile antenna. In the real world, I try to avoid short antennas.. :) It's only a last resort due to lack of room. I rarely actually use one. |
Let's design a short antenna just for fun
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Let's design a short antenna just for fun
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Let's design a short antenna just for fun
On Wednesday, November 5, 2014 1:33:06 PM UTC-6, rickman wrote:
On 11/5/2014 2:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. What? Maybe you don't fully grasp the idea of a "short" antenna? ;-) -- Rick I grasp that the shorter the antenna, the worse it generally performs. But if I use an 18 ft long dipole for 80 or 40 meters, I consider that a short dipole. Others may disagree, but I don't care. They can knock themselves out with shorter versions. I try to avoid using short dipoles. My previously mentioned methods can be used with any length dipole. The smaller, the smaller the performance. :( Of course, the reasons for the smaller performance are not what he who is silly thinks are the reasons. :| |
Let's design a short antenna just for fun
On Wednesday, November 5, 2014 1:46:18 PM UTC-6, wrote:
wrote: On Wednesday, November 5, 2014 1:01:02 PM UTC-6, I would think a dipole would be a bad candidate for a "short" antenna as you need to get the matching stuff close to the antenna to avoid I^2R losses. I'd probably use small matching coils at the feed point, about the same as a mobile antenna. There is a lot of stuff out there that says the best place to put a loading coil is somewhere between 1/2 and 3/4 of the way up. My usual 11 ft 80-10m mobile antenna in the driving mode is exactly center loaded. The coil bottom is at the 5 ft point, and there is a 5 ft "stinger whip" above it. The coil itself is about a foot long and has taps for the various bands. I use shorter stinger whips for the higher bands. But in the parked mode, I have a solid three foot mast that I screw onto the base of the main whip, and the coil is at the 8ft level. It makes quite a difference in efficiency. I don't use a hat on my mobile antennas because I think they are ugly, and catch too much wind. I also have a screwdriver antenna I got free, but it's inferior to my homemade "plastic bugcatchers", and I've never used it. It sits in the garage and collects dust. :( I've used a 706mk2g as the mobile rig since about 2001 or so. But I recently picked up a FT-100 which could be used also. I also have the matching auto tuner for that rig, but not sure if I would ever use it. I don't need it for my usual mobile whips as they are matched with the "dollar special" matching coils. It should be fairly easy to model to see where it would be for various total lengths. Yep.. I think vertload will do it if I'm remembering the right program. In the real world, I try to avoid short antennas.. :) It's only a last resort due to lack of room. I rarely actually use one. Me too for the most part. I've never felt a need to go mobile any lower than 10M though I have put some thought into shortning 160M antennas. I've had a 80-10 mobile antenna for many years. When parked, I've used it on 160m by clipping on a longer wire above the coil. Both of my trucks have antenna ball mounts. But the Toyota car I drive does not have anything, because I'm chicken to booger up the pristine body with holes and such.. :/ One concept I started playing with but never finished was the folded monopole, i.e. half of a folded dipole, but with more than one "folded" element in an attempt to get the radiation resistance up. I've never tried anything like that. |
Let's design a short antenna just for fun
On Wednesday, November 5, 2014 2:04:29 PM UTC-6, wrote:
My usual 11 ft 80-10m mobile antenna in the driving mode is exactly center loaded. The coil bottom is at the 5 ft point, Hummm, that is wrong. The base of the coil is at the 6 ft level, not 5.. |
Let's design a short antenna just for fun
On Wednesday, November 5, 2014 2:16:04 PM UTC-6,
There is little practical reason for shortning 23 cm band antenna, but antennas for 160M are a challenge for most people that live in an urban area. Where I live anything over about 30 feet tall is basically a no-go. So in the interest of practicallity and maybe getting something usefull out of it, how about a 160M antenna with a maximum height of 30 feet as a goal? That immediately eliminates dipoles as a 160M dipole at 30 feet will radiate most of the power straight up. In that case, I'd use a "T" vertical, with the loading coil at the base if the top wires are too short to tune the antenna. The main reason for having the coil at the base is ease of changing the inductance, and the top hat wires improve current distribution vs a whip with no top wires. If no room for the top wires, I'd use a capacity hat if possible. |
Let's design a short antenna just for fun
On 11/5/2014 1:32 PM, rickman wrote:
On 11/5/2014 2:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. What? Maybe you don't fully grasp the idea of a "short" antenna? ;-) Rickman, please. Is that the tact a Gentleman would use? It seems that your comment may be designed to invoke an ungentlemanly response. This is exactly the sort of response I was hoping to avoid. I beg you to be a bit more tactful. For example "Well, of course, but what do you, personally, consider is a short antenna?" |
Let's design a short antenna just for fun
On 11/5/2014 1:43 PM, wrote:
On Wednesday, November 5, 2014 1:33:06 PM UTC-6, rickman wrote: On 11/5/2014 2:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. What? Maybe you don't fully grasp the idea of a "short" antenna? ;-) -- Rick I grasp that the shorter the antenna, the worse it generally performs. But if I use an 18 ft long dipole for 80 or 40 meters, I consider that a short dipole. Others may disagree, but I don't care. They can knock themselves out with shorter versions. I try to avoid using short dipoles. My previously mentioned methods can be used with any length dipole. The smaller, the smaller the performance. :( Of course, the reasons for the smaller performance are not what he who is silly thinks are the reasons. :| C'mon, Mark. You didn't need to add that. I think all of your technical responses have been excellent info. Good man. |
Let's design a short antenna just for fun
On Wednesday, November 5, 2014 2:26:23 PM UTC-6, John S wrote:
C'mon, Mark. You didn't need to add that. I think all of your technical responses have been excellent info. Good man. Yea, I know, but he has a way of provoking me that is hard to resist.. |
Let's design a short antenna just for fun
On 11/5/2014 1:02 PM, wrote:
On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. And all the other parameters can be adjusted also.. You use what you can get away with to fit the room you have. I don't recall having any mobile whips modeled, but it's hard to say as all the older designs I did are on older unused hard drives and I don't have ready access to them. I had to re-download quite a few programs due to that reason.. I change drives quite often. I just added two more 2 TB drives about a month ago.. I have several TB these days. All of Reg's old software can still be downloaded. http://zerobeat.net/G4FGQ/page3.html#S301%22 Vertload was one I used a lot for playing "what if" when designing mobile whips and other short verticals, and the info can easily be used for small dipoles. There are others programs that can be handy also. It's been a long time since I used it, but I believe vertload can be used to locate the best location on the whip to place the loading coil. In general, you want it as far out to the ends as possible for the best current distribution, but there is a point where coil losses start to outweigh the improved current distribution. So in the real world, the best location is usually appx 3/4 the way out from the feedpoint, plus or minus. And the use of capacity hats further improve current distribution, and slightly reduce the number of turns needed for the loading coil. A short dipole is never going to be quite as good as a full size version, but with proper design you can come up with quite a respectable antenna given the dinky size. John (who was KD5YI but will be N1JLS in a few weeks due to vanity) Hummm.. You now in 1 land, or you just grabbing an old call? My current call is a vanity call, which I think I've had since '96. I was WD5CJL in a past life.. I got that call in 77 when I was 20. Grabbing an unused call sign. Don't know exactly why. My initials are JLS and I thought N1 would be Number 1! So that would make me Number 1 John L Smith. How vain is that? I actually got into ham radio when I was in the eighth grade, learned the code, and even built a 6v6 transmitter from junk parts. Woo hoo! Me, too. Mine was a 6L6. First contact from Dallas in the middle of the day was Oklahoma City on a wire dipole. CW of course. Got my ticket in 1957 while in high school. KN5SIW. I still have the paper license the FCC gave me. In those days you had to upgrade within a year or loose it, so I became K5SIW. But then I got lazy and kind of got out of it a while, and didn't actually get a ticket. Later on I got back into it, and got a ticket about six years later. I used my first 6v6 transmitter when I was a novice in 77. I was a SWL for a good while before I got into ham radio. I worked a lot of CW back in the old days. I got up to nearly 60 wpm at one point. But due to lack of activity the past several years, I can't do near that now. :( I never made it to more than about 15 or so WPM. Family and career took precedence. I doubt I could do 5 WPM now. Lack of activity. But, there is still something I like about code, and I don't understand what it is. |
Let's design a short antenna just for fun
wrote in message
... Yea, I know, but he has a way of provoking me that is hard to resist.. How does speaking the truth provoke you? |
Let's design a short antenna just for fun
|
Let's design a short antenna just for fun
On Wednesday, November 5, 2014 2:35:40 PM UTC-6, John S wrote:
On 11/5/2014 1:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. And all the other parameters can be adjusted also.. You use what you can get away with to fit the room you have. I don't recall having any mobile whips modeled, but it's hard to say as all the older designs I did are on older unused hard drives and I don't have ready access to them. I had to re-download quite a few programs due to that reason.. I change drives quite often. I just added two more 2 TB drives about a month ago.. I have several TB these days. All of Reg's old software can still be downloaded. http://zerobeat.net/G4FGQ/page3.html#S301%22 Vertload was one I used a lot for playing "what if" when designing mobile whips and other short verticals, and the info can easily be used for small dipoles. There are others programs that can be handy also. It's been a long time since I used it, but I believe vertload can be used to locate the best location on the whip to place the loading coil. In general, you want it as far out to the ends as possible for the best current distribution, but there is a point where coil losses start to outweigh the improved current distribution. So in the real world, the best location is usually appx 3/4 the way out from the feedpoint, plus or minus. And the use of capacity hats further improve current distribution, and slightly reduce the number of turns needed for the loading coil. A short dipole is never going to be quite as good as a full size version, but with proper design you can come up with quite a respectable antenna given the dinky size. John (who was KD5YI but will be N1JLS in a few weeks due to vanity) Hummm.. You now in 1 land, or you just grabbing an old call? My current call is a vanity call, which I think I've had since '96. I was WD5CJL in a past life.. I got that call in 77 when I was 20. Grabbing an unused call sign. Don't know exactly why. My initials are JLS and I thought N1 would be Number 1! So that would make me Number 1 John L Smith. How vain is that? No more than mine, which the M and the K are my initials. I really wanted W5MK, and I was going to grab it as the guy lived here locally, and I knew he went SK. But I had to wait 2 years, and when it come up for grabs, I had forgot about it, and someone else hopped on it. But I much prefer what I have now, vs my old call. Many used to confuse the L for an O on phone, and the new call is lickity split fast on CW vs the old call. |
Let's design a short antenna just for fun
"John S" wrote in message
... Please, Mark. Try. I am pleased that my exhortations that you should improve your previous behaviour have taken effect. Well done! Keep up the good work! |
Let's design a short antenna just for fun
On 11/5/2014 2:42 PM, wrote:
On Wednesday, November 5, 2014 2:35:40 PM UTC-6, John S wrote: On 11/5/2014 1:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. And all the other parameters can be adjusted also.. You use what you can get away with to fit the room you have. I don't recall having any mobile whips modeled, but it's hard to say as all the older designs I did are on older unused hard drives and I don't have ready access to them. I had to re-download quite a few programs due to that reason.. I change drives quite often. I just added two more 2 TB drives about a month ago.. I have several TB these days. All of Reg's old software can still be downloaded. http://zerobeat.net/G4FGQ/page3.html#S301%22 Vertload was one I used a lot for playing "what if" when designing mobile whips and other short verticals, and the info can easily be used for small dipoles. There are others programs that can be handy also. It's been a long time since I used it, but I believe vertload can be used to locate the best location on the whip to place the loading coil. In general, you want it as far out to the ends as possible for the best current distribution, but there is a point where coil losses start to outweigh the improved current distribution. So in the real world, the best location is usually appx 3/4 the way out from the feedpoint, plus or minus. And the use of capacity hats further improve current distribution, and slightly reduce the number of turns needed for the loading coil. A short dipole is never going to be quite as good as a full size version, but with proper design you can come up with quite a respectable antenna given the dinky size. John (who was KD5YI but will be N1JLS in a few weeks due to vanity) Hummm.. You now in 1 land, or you just grabbing an old call? My current call is a vanity call, which I think I've had since '96. I was WD5CJL in a past life.. I got that call in 77 when I was 20. Grabbing an unused call sign. Don't know exactly why. My initials are JLS and I thought N1 would be Number 1! So that would make me Number 1 John L Smith. How vain is that? No more than mine, which the M and the K are my initials. I really wanted W5MK, and I was going to grab it as the guy lived here locally, and I knew he went SK. But I had to wait 2 years, and when it come up for grabs, I had forgot about it, and someone else hopped on it. But I much prefer what I have now, vs my old call. Many used to confuse the L for an O on phone, and the new call is lickity split fast on CW vs the old call. Your sign is to be envied. Good for you! |
Let's design a short antenna just for fun
On 11/5/2014 2:43 PM, wrote:
On Wednesday, November 5, 2014 1:33:06 PM UTC-6, rickman wrote: On 11/5/2014 2:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. What? Maybe you don't fully grasp the idea of a "short" antenna? ;-) -- Rick I grasp that the shorter the antenna, the worse it generally performs. You are starting to sound like you-know-who now! But if I use an 18 ft long dipole for 80 or 40 meters, I consider that a short dipole. Others may disagree, but I don't care. They can knock themselves out with shorter versions. I try to avoid using short dipoles. My previously mentioned methods can be used with any length dipole. The smaller, the smaller the performance. :( Of course, the reasons for the smaller performance are not what he who is silly thinks are the reasons. :| Hmmm... ok. So you are happy discussing short antenna as long as they aren't *too* short. -- Rick |
Let's design a short antenna just for fun
On 11/5/2014 3:21 PM, John S wrote:
On 11/5/2014 1:32 PM, rickman wrote: On 11/5/2014 2:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. What? Maybe you don't fully grasp the idea of a "short" antenna? ;-) Rickman, please. Is that the tact a Gentleman would use? It seems that your comment may be designed to invoke an ungentlemanly response. This is exactly the sort of response I was hoping to avoid. I beg you to be a bit more tactful. Chill dude. Did you see the smiley? It was meant to be humorous. For example "Well, of course, but what do you, personally, consider is a short antenna?" Hey! Who are you calling short? -- Rick |
Let's design a short antenna just for fun
On 11/5/2014 5:41 PM, rickman wrote:
On 11/5/2014 3:21 PM, John S wrote: On 11/5/2014 1:32 PM, rickman wrote: On 11/5/2014 2:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. What? Maybe you don't fully grasp the idea of a "short" antenna? ;-) Rickman, please. Is that the tact a Gentleman would use? It seems that your comment may be designed to invoke an ungentlemanly response. This is exactly the sort of response I was hoping to avoid. I beg you to be a bit more tactful. Chill dude. Did you see the smiley? It was meant to be humorous. For example "Well, of course, but what do you, personally, consider is a short antenna?" Hey! Who are you calling short? ;-) -- Rick |
Let's design a short antenna just for fun
|
Let's design a short antenna just for fun
On 11/5/2014 4:41 PM, rickman wrote:
On 11/5/2014 3:21 PM, John S wrote: On 11/5/2014 1:32 PM, rickman wrote: On 11/5/2014 2:02 PM, wrote: On Wednesday, November 5, 2014 12:33:48 PM UTC-6, John S wrote: Can you tell us how big would it be? And what about the coil dimensions, losses? Can you do an EZNEC model so those of us who have the simulator can look at all the parameters/arguments? It can be any size one wants. The bigger the better of course.. What? Maybe you don't fully grasp the idea of a "short" antenna? ;-) Rickman, please. Is that the tact a Gentleman would use? It seems that your comment may be designed to invoke an ungentlemanly response. This is exactly the sort of response I was hoping to avoid. I beg you to be a bit more tactful. Chill dude. Did you see the smiley? It was meant to be humorous. Sorry. I miss noticing those frequently. For example "Well, of course, but what do you, personally, consider is a short antenna?" Hey! Who are you calling short? |
Let's design a short antenna just for fun
On 11/6/2014 7:16 AM, amdx wrote:
On 11/5/2014 1:08 PM, wrote: On Wednesday, November 5, 2014 1:01:02 PM UTC-6, I would think a dipole would be a bad candidate for a "short" antenna as you need to get the matching stuff close to the antenna to avoid I^2R losses. I'd probably use small matching coils at the feed point, about the same as a mobile antenna. In the real world, I try to avoid short antennas.. :) It's only a last resort due to lack of room. I rarely actually use one. OK, nuff jabbering. I'll set the rules 15ft tall, designed for 80 meters. 16 radials, base mounted inductor and whatever tophat you desire. Do the theoretical design find the feed impedance with some efficiency numbers. Then compare data to a dipole at 1/4 wave height. Ready Set GO! Wait, do you have a better idea than a base mounted inductor? How long are the radials? Do you want to compare 8 to 16 radials. The tophat needs to survive 80 mile an hr wind. I'm sure there's more. Mikek What wire material/size? Some stainless steel rods might have a permeability that will reduce the efficiency. It will certainly have a higher resistance than copper. Also note that copper-clad steel must have a cladding several times the skin depth for high efficiency. John |
Let's design a short antenna just for fun
On 11/6/2014 7:16 AM, amdx wrote:
On 11/5/2014 1:08 PM, wrote: On Wednesday, November 5, 2014 1:01:02 PM UTC-6, I would think a dipole would be a bad candidate for a "short" antenna as you need to get the matching stuff close to the antenna to avoid I^2R losses. I'd probably use small matching coils at the feed point, about the same as a mobile antenna. In the real world, I try to avoid short antennas.. :) It's only a last resort due to lack of room. I rarely actually use one. OK, nuff jabbering. I'll set the rules 15ft tall, designed for 80 meters. 16 radials, base mounted inductor and whatever tophat you desire. Do the theoretical design find the feed impedance with some efficiency numbers. Then compare data to a dipole at 1/4 wave height. Ready Set GO! Wait, do you have a better idea than a base mounted inductor? As Mark said, maybe 50-75% along the antenna. How long are the radials? How much space can you give us? Do you want to compare 8 to 16 radials. We can do that. (Or you can do it yourself with EZNEC) The tophat needs to survive 80 mile an hr wind. I don't know how to do that. I'm sure there's more. Yes, always. Mikek John |
Let's design a short antenna just for fun
On Thursday, November 6, 2014 7:16:32 AM UTC-6, amdx wrote:
OK, nuff jabbering. I'll set the rules 15ft tall, designed for 80 meters. 16 radials, base mounted inductor and whatever tophat you desire. Do the theoretical design find the feed impedance with some efficiency numbers. Then compare data to a dipole at 1/4 wave height. Ready Set GO! I'll let you all do the actual design and calculating. All of the software needed can be had free on the web. Wait, do you have a better idea than a base mounted inductor? If you use a large enough hat, it really doesn't matter where the coil is as far as improving current distribution. How long are the radials? I dunno.. how much wire is available? How much room? In general for a limited amount of wire, many short radials are better than just a few long ones. Do you want to compare 8 to 16 radials. Neither one is really enough for top performance over avg ground with a short vertical. The tophat needs to survive 80 mile an hr wind. Use guyed off wire spokes I suppose.. It depends on the path/distance, etc but in general a 1/2 wl dipole at 1/4 wave is going to smoke most any short vertical of that appx design. NVIS, HUGELY so.. far DX, might be a toss if the vertical is performing well. But to really perform well, I'd want at least 60 radials, not 8-16.. In the real world, I generally wouldn't use such an antenna unless it was all I could get away with. With ground mount verticals, the shorter the antenna, the more critical the ground radial system becomes. On 80m, 99 percent of my jibber jabber is NVIS, and I'd be the laughing stock of the frequency with such an antenna. My signal would be quite puny, compared to my normal dipoles and such. I'd be heckled and tormented endlessly to build a "real" antenna. I ain't joking either. They can be a tough crowd out there. lol |
Let's design a short antenna just for fun
Jeff wrote:
I would think a dipole would be a bad candidate for a "short" antenna as you need to get the matching stuff close to the antenna to avoid I^2R losses. Some sort of ground mounted, or close to the ground, antenna might make a better choice. A dipole may be a better candidate, if you use a monopole then although you will be able to put your matching close to the antenna, providing an effective earth screen becomes vital and earth losses may outweigh any advantage. Of course if you do use a dipole it is vital that any matching is at the feed point and not on the end of a length of coax or the losses will soar. The issue with dipoles is height. As the height of a dipole decreases below 1/2 wavelength the pattern elevation angle starts increasing and very quickly has most of the energy going straight up. At 160M that means getting the dipole 260 feet up in the air, and if you can do that, why would you be concerned about a short antenna as a full 1/4 wave 160M antenna is only about 140 feet tall? -- Jim Pennino |
Let's design a short antenna just for fun
On Thursday, November 6, 2014 12:46:04 PM UTC-6, wrote:
Jeff wrote: I would think a dipole would be a bad candidate for a "short" antenna as you need to get the matching stuff close to the antenna to avoid I^2R losses. Some sort of ground mounted, or close to the ground, antenna might make a better choice. A dipole may be a better candidate, if you use a monopole then although you will be able to put your matching close to the antenna, providing an effective earth screen becomes vital and earth losses may outweigh any advantage. Of course if you do use a dipole it is vital that any matching is at the feed point and not on the end of a length of coax or the losses will soar. The issue with dipoles is height. As the height of a dipole decreases below 1/2 wavelength the pattern elevation angle starts increasing and very quickly has most of the energy going straight up. At 160M that means getting the dipole 260 feet up in the air, and if you can do that, why would you be concerned about a short antenna as a full 1/4 wave 160M antenna is only about 140 feet tall? -- Jim Pennino When I was on 160m a lot, I had both the T vertical, and I also had a "Z" dipole, which was the only way I could fit a dipole on this lot without loading coils. In some cases for NVIS, the Z dipole was a bit better, but overall, I prefer being vertical on 160. On that band, the path doesn't really have to be that far for the vertical to do as well or better than the very low dipole. And at farther distances, the vertical will generally outperform the low dipole by quite a large margin. So if I could could only have one antenna, I would generally prefer the vertical, because a dipole on that band really needs to be pretty high to play well. My Z dipole was only at about 40 feet at the apex, which is only slightly above 1/16 of a wave up. :( It was fairly lame overall. W8JI plays on 160m a lot, and has lots of good info about that band and his various antennas on his web site, if it's still around. I haven't looked at it in a while. |
Let's design a short antenna just for fun
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Let's design a short antenna just for fun
On 11/6/2014 10:56 AM, John S wrote:
On 11/6/2014 7:16 AM, amdx wrote: On 11/5/2014 1:08 PM, wrote: On Wednesday, November 5, 2014 1:01:02 PM UTC-6, I would think a dipole would be a bad candidate for a "short" antenna as you need to get the matching stuff close to the antenna to avoid I^2R losses. I'd probably use small matching coils at the feed point, about the same as a mobile antenna. In the real world, I try to avoid short antennas.. :) It's only a last resort due to lack of room. I rarely actually use one. OK, nuff jabbering. I'll set the rules 15ft tall, designed for 80 meters. 16 radials, base mounted inductor and whatever tophat you desire. Do the theoretical design find the feed impedance with some efficiency numbers. Then compare data to a dipole at 1/4 wave height. Ready Set GO! Wait, do you have a better idea than a base mounted inductor? As Mark said, maybe 50-75% along the antenna. How long are the radials? How much space can you give us? Do you want to compare 8 to 16 radials. We can do that. (Or you can do it yourself with EZNEC) The tophat needs to survive 80 mile an hr wind. I don't know how to do that. I'm sure there's more. Yes, always. I don't have a radio so it is moot point to me. I was just trying to get a design going, as there just seemed to be a lot of jabbering. But, there are just so many variables and you do need to start with a location, how much money are you going to spend, what materials can you get, and then design around them. I'm not an actual ham but I did read Jerry Sevicks book, "The Short Vertical Antenna and Ground Radial" http://tinyurl.com/p3rp2qe Mikek |
Let's design a short antenna just for fun
On Friday, November 7, 2014 11:22:30 PM UTC-6, amdx wrote:
I don't have a radio so it is moot point to me. I was just trying to get a design going, as there just seemed to be a lot of jabbering. But, there are just so many variables and you do need to start with a location, how much money are you going to spend, what materials can you get, and then design around them. I'm not an actual ham but I did read Jerry Sevicks book, "The Short Vertical Antenna and Ground Radial" http://tinyurl.com/p3rp2qe Mikek With me, I just don't have time to do something I've already done several times years ago.. I know pretty much from what I've already modeled, what works and what doesn't. I used to have loads and loads of stored antennas I modeled, but like I say, it's all on old drives I don't use any more. As I seem to recall, Jerry Sevick knows his stuff, so you won't go wrong with that book. |
Let's design a short antenna just for fun
amdx wrote in :
what materials can you get, and then design around them. I'll risk looking like a devil's advocate here and suggest good austenitic stainless steel, like 316, for wires and radials, as a first base. Reasons: 1. Cheaper than copper. 2. Stronger than copper. 3. If after a bit of stretching, a strong NdFeB magnet shows total indifference to it when introduced, it permeability is likely low enough to ignore if you're doing a first, empirical test of an antenna. 4. Very good chemical resistance, eliminating a whole heap of environmental concerns for its endurance and performance. 5. Very good physical resistance, so no need to cover with insulator, thus no need to add that into high frequency modelling. 6. Easy to find all over eBay... I'm sure there are things I didn't think of, and if there is some vitally specific reason not to do this, you'll likely already know it, but my point is that if you just want to get something tried out first, economically, it is likely better this way than starting with copper, for the simple reason that if it fails, the stainless stuff will do you good service in some other way, sometime, and wasted copper is less useful, and loses money very fast. |
Let's design a short antenna just for fun
After posting, I remembered one important one, electrical resistance. That
might strongly reject austenitic stainless as a choice, if the antenna is small or otherwise makes low resistance critical. On the other hand its high strwength to weight ratio might be another strong plus to add to any others, it can save nasty accidents with underestimating wind loads, breaking strains and such when testing a new build. (For wires, I'm less sure about towers, I haven't learned enough to make suggestions for materials and structural forms and dimensions for those). |
Let's design a short antenna just for fun
On 11/8/2014 5:22 AM, Lostgallifreyan wrote:
After posting, I remembered one important one, electrical resistance. That might strongly reject austenitic stainless as a choice, if the antenna is small or otherwise makes low resistance critical. As far as I can tell by modelling, SS does have a bit higher resistance than copper, but it is the permeability that kills it for a radiator. I would definitely go for low-permeability SS over copper in an appropriate situation. On the other hand its high strwength to weight ratio might be another strong plus to add to any others, it can save nasty accidents with underestimating wind loads, breaking strains and such when testing a new build. (For wires, I'm less sure about towers, I haven't learned enough to make suggestions for materials and structural forms and dimensions for those). |
Let's design a short antenna just for fun
Lostgallifreyan wrote:
After posting, I remembered one important one, electrical resistance. That might strongly reject austenitic stainless as a choice, if the antenna is small or otherwise makes low resistance critical. On the other hand its high strwength to weight ratio might be another strong plus to add to any others, it can save nasty accidents with underestimating wind loads, breaking strains and such when testing a new build. (For wires, I'm less sure about towers, I haven't learned enough to make suggestions for materials and structural forms and dimensions for those). The resistivity of stainless steel is about 35 times that of copper and about 20 times that of aluminum. This will make a big difference for a wire antenna, but less for one of fat tubing or rod, however stainless tubing is both heavy and expensive. It would all be a bunch of engineering trade offs that would depend on what one wants to accomplish. If it happens that your brother-in-law can get you stainless at a good price... -- Jim Pennino |
Let's design a short antenna just for fun
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