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Radials
I've been doing a bit of reading and wonder about the following.
In a number of places I've read that in the case of a short vertical antenna. the radials need be no longer than the height of the antenna which in my case is about 8 ft. Even then I will be pressed to spread out the currently planned eight 9ft. radials on my small balcony. I'll have wire all over the place but once I get things working I hope to lay a bit of outdoor carpeting over the radials to make things look a little neater. No way will I be able to go 120 radials!! And there is no real practical way of putting out off ground radials for each band! The snow is still falling here!!! -- but I'm optimistic that by the end of may I should be able to move things outside onto the balcony and start playing. Any comments or ideas will be welcome. Irv VE6BP |
Radials
Irv Finkleman wrote:
I've been doing a bit of reading and wonder about the following. In a number of places I've read that in the case of a short vertical antenna. the radials need be no longer than the height of the antenna which in my case is about 8 ft. Even then I will be pressed to spread out the currently planned eight 9ft. radials on my small balcony. I'll have wire all over the place but once I get things working I hope to lay a bit of outdoor carpeting over the radials to make things look a little neater. No way will I be able to go 120 radials!! And there is no real practical way of putting out off ground radials for each band! For an elevated antenna, 3-4 radials are generally enough. The 120 applies to radials on, in, or very very near the ground. The snow is still falling here!!! -- but I'm optimistic that by the end of may I should be able to move things outside onto the balcony and start playing. Any comments or ideas will be welcome. Irv VE6BP -- Jim Pennino |
Radials
On 3/31/2014 10:38 PM, Irv Finkleman wrote:
I've been doing a bit of reading and wonder about the following. In a number of places I've read that in the case of a short vertical antenna. the radials need be no longer than the height of the antenna which in my case is about 8 ft. Even then I will be pressed to spread out the currently planned eight 9ft. radials on my small balcony. I'll have wire all over the place but once I get things working I hope to lay a bit of outdoor carpeting over the radials to make things look a little neater. No way will I be able to go 120 radials!! And there is no real practical way of putting out off ground radials for each band! The snow is still falling here!!! -- but I'm optimistic that by the end of may I should be able to move things outside onto the balcony and start playing. Any comments or ideas will be welcome. Irv VE6BP Florida is nice this time of year :) Jerry, AI0K -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
Radials
In article ,
"Irv Finkleman" wrote: In a number of places I've read that in the case of a short vertical antenna. the radials need be no longer than the height of the antenna which in my case is about 8 ft. Even then I will be pressed to spread out the currently planned eight 9ft. radials on my small balcony. I'll have wire all over the place but once I get things working I hope to lay a bit of outdoor carpeting over the radials to make things look a little neater. Irv- You do what you can. If you can tune the antenna for a match, you're on the air! In my experience, a short antenna such as a Hamstick does not work well on 75 or 40 Meters using this method, especially with such short radials. Adding radials may help, especially on the higher bands. If you have a metal balcony rail, make a connection to the rail at the base of the antenna, and run the radials from there. A clamp used with a ground rod may work. Or you might use a trucker's CB mirror mount to both make a ground connection and mount the antenna. Example: http://www.amazon.com/MIRROR-MOUNT-A...t/dp/B004X84B5 K Fred K4DII |
Radials
El 01-04-14 4:38, Irv Finkleman escribió:
I've been doing a bit of reading and wonder about the following. In a number of places I've read that in the case of a short vertical antenna. the radials need be no longer than the height of the antenna which in my case is about 8 ft. Even then I will be pressed to spread out the currently planned eight 9ft. radials on my small balcony. I'll have wire all over the place but once I get things working I hope to lay a bit of outdoor carpeting over the radials to make things look a little neater. No way will I be able to go 120 radials!! Don't worry, it doesn't say that using less radials turns your antenna into a dummy load. Just connect as much metal you can find together to make a non-resonant ground provision. Of course the overall antenna efficiency will be less compared to a full size vertical with a solid floating or burried ground, but an antenna with 10% radiation efficiency is always better then no antenna. Don't forget to add some common mode provision (ferrite choke) where the cable enters the shack. Local interference may even be a bigger problem. And there is no real practical way of putting out off ground radials for each band! The snow is still falling here!!! -- but I'm optimistic that by the end of may I should be able to move things outside onto the balcony and start playing. Any comments or ideas will be welcome. Irv VE6BP -- Wim PA3DJS Please remove abc first in case of PM |
Radials on a elevated antenna only works if the radials are placed at or near the bottom of the antenna and are arranged at a 45* angle.
Any other angle and you might as well not have any radials at all! On a 10 -12 meter antenna, these radials would need to be at least 1/4 of a wavelength long - 9 feet and preferably 18 feet long to do any good! If you coil them up they do not work as intended, but they might help a little. Forget calling them a ground plane, think of them more like a mirror. If you shine a beam of light directly at a mirror, the light is 100% reflected back towards the source. If most of your radiated power is located at the bottom of the antenna and you can reflect that power up and forward - it is going to radiate better then something that is only partially effective. Anything that you don't reflect is adsorbed into the ground - good for keeping the worms warm at night, but not good for radiating RF.. Only a fool would become a ham and then move into an apartment! The sad truth is that most people do not understand what being a ham is all about anymore and most people thinks that amateur radio is a right and not a privilege. Trying to be a ham while living in an apartment building would be like trying to be a Ocean liner captain while living in Oklahoma... The metal railing is much too small in rf area to be an effective counter poise - sorry but who ever told you this should go back to school and get a real education. |
Radials
El 01-04-14 19:21, Channel Jumper escribió:
Radials on a elevated antenna only works if the radials are placed at or near the bottom of the antenna and are arranged at a 45* angle. Any other angle and you might as well not have any radials at all! I don't support this reasoning, I see many good antennas that don't follow this rule. On a 10 -12 meter antenna, these radials would need to be at least 1/4 of a wavelength long - 9 feet and preferably 18 feet long to do any good! If you coil them up they do not work as intended, but they might help a little. Forget calling them a ground plane, think of them more like a mirror. I see the ground provision just as a means to pull out the current that goes into the radiator (as I don't want to draw this current out of the braid). If 1 A goes into the radiator, I need to draw 1 A from my ground/counterpoise/etc. I would like to have the resistance of the ground provision small with respect to the real part of the radiator's impedance. If you shine a beam of light directly at a mirror, the light is 100% reflected back towards the source. I think you can't compare the light analogy with a situation where the wavelength is no long small compared to the structure. A ground provision can be good enough for a well-designed half-wave end-fed antenna, but useless for a quarter wave whip. You can't explain this with light analogy. If most of your radiated power is located at the bottom of the antenna and you can reflect that power up and forward - it is going to radiate better then something that is only partially effective. Anything that you don't reflect is adsorbed into the ground - good for keeping the worms warm at night, but not good for radiating RF.. Only a fool would become a ham and then move into an apartment! Sometimes you don't have another choice and then you need to get the best out of it. The sad truth is that most people do not understand what being a ham is all about anymore and most people thinks that amateur radio is a right and not a privilege. Trying to be a ham while living in an apartment building would be like trying to be a Ocean liner captain while living in Oklahoma... The metal railing is much too small in rf area to be an effective counter poise - sorry but who ever told you this should go back to school and get a real education. It all depends on the current you need to draw from it, given certain power. You will certainly not get good radiation efficiency, but this doesn't say it is useless. Given the good conditions at the upper end of HF, you can get useful efficiency from a small antenna. -- Wim PA3DJS Please remove abc first in case of PM |
Radials
Channel Jumper wrote:
Radials on a elevated antenna only works if the radials are placed at or near the bottom of the antenna and are arranged at a 45* angle. Any other angle and you might as well not have any radials at all! Utter nonsense. The radials do have to be at or near the bottom but the angle of the radials mostly determines the antenna impedance. With the radials at 90 degrees the impedance will be around 40 Ohms and at 45 degees very close to 50 Ohms. One can download the demo version of EZNEC and observe the effect of radial angle for themselves. On a 10 -12 meter antenna, these radials would need to be at least 1/4 of a wavelength long - 9 feet and preferably 18 feet long to do any good! The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. If you coil them up they do not work as intended, but they might help a little. If you coil them up, you are inductively loading them, shortening the physical length just like a loaded vertical. If you make them electrically around 1/4 wavelength, loaded radials will work just fine. Ground plane antennas have been made with 4 hamsticks; 1 for the vertical element and 3 for the radials and they work. They major drawback to such is the limited bandwidth of loaded antennas. snip remaining babbling nonsense -- Jim Pennino |
Radials
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Radials
On Wednesday, April 2, 2014 3:04:29 AM UTC-5, Ian Jackson wrote:
I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. Doesn't making the radials a bit long and the monopole a bit short raise the feedpoint resistance? Sorta like an OCF dipole? |
Radials
In message ,
W5DXP writes On Wednesday, April 2, 2014 3:04:29 AM UTC-5, Ian Jackson wrote: I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. Doesn't making the radials a bit long and the monopole a bit short raise the feedpoint resistance? Sorta like an OCF dipole? But won't you have to shorten the antenna a little to maintain resonance? -- Ian |
Radials
On 4/1/2014 12:21 PM, Channel Jumper wrote:
Radials on a elevated antenna only works if the radials are placed at or near the bottom of the antenna and are arranged at a 45* angle. Obviously you have not been doing antennas very long. This statement above is absurd and everyone here who has been making antennas or just using them for any length of time knows this. Making this kind of ridiculous statement removes all your credibility. Do a little research before saying such silly things. Any other angle and you might as well not have any radials at all! Again, just wrong and destroys any cred you might have had here. On a 10 -12 meter antenna, these radials would need to be at least 1/4 of a wavelength long - 9 feet and preferably 18 feet long to do any good! 1/4 wavelength works just fine. Longer does not help. If you coil them up they do not work as intended, but they might help a little. Forget calling them a ground plane, think of them more like a mirror. If you shine a beam of light directly at a mirror, the light is 100% reflected back towards the source. Electromagnetic energy is not the same as light. Look that up. If most of your radiated power is located at the bottom of the antenna and you can reflect that power up and forward - it is going to radiate better then something that is only partially effective. Anything that you don't reflect is adsorbed into the ground - good for keeping the worms warm at night, but not good for radiating RF.. Only a fool would become a ham and then move into an apartment! Look who is calling someone a fool. The sad truth is that most people do not understand what being a ham is all about anymore and most people thinks that amateur radio is a right and not a privilege. Keep trying to understand what being a ham is supposed to be. You might get there. Trying to be a ham while living in an apartment building would be like trying to be a Ocean liner captain while living in Oklahoma... Some hams are forced into an apartment by economic forces. They can still be a ham and operate. Your analogy sucks. The metal railing is much too small in rf area to be an effective counter poise - sorry but who ever told you this should go back to school and get a real education. You would not know anyway. |
Radials
Ian Jackson wrote:
In message , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. -- Jim Pennino |
Radials
In message ,
writes Ian Jackson wrote: In message , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. Yebbut ........ You've just said "the ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequency". I assumed that "ideal" = "best". .. All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. True - but what's the angle of the radials got to do with their length? I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. I had presumed you had already do this (or something similar) in order to say that slightly longer than a 1/4 wavelength was ideal. However, I have always assumed that the steeper the angle of the radials, the more the groundplane becomes like a vertical halfwave dipole - and the lower becomes the angle of radiation. -- Ian |
Radials
El 02-04-14 20:25, Ian Jackson escribió:
In message , writes Ian Jackson wrote: In message , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. Yebbut ........ You've just said "the ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequency". I assumed that "ideal" = "best". . All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. True - but what's the angle of the radials got to do with their length? I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. I had presumed you had already do this (or something similar) in order to say that slightly longer than a 1/4 wavelength was ideal. However, I have always assumed that the steeper the angle of the radials, the more the groundplane becomes like a vertical halfwave dipole - and the lower becomes the angle of radiation. You are right, very steep radials become the lower half of a half wave dipole as the currents do not cancel eachother and contribute to the field of the quarter wave monopole. The "ultimate" version is the sleeve dipole. When they are in the horizontal plane, the contribution to the total radiation pattern is very small, and the contribution from the radials is even zero for the vertically polarized component at zero elevation. The "somewhat longer then 1/4 wavelength" I also noticed with radials connected to a coaxial braid to form a narrow band common mode choke. the choking effect (common mode insertion loss) is better when they are somewhat longer then 0.25lambda (depending in thickness). The effect of sloping angle on zero elevation gain is small, and you get hardly measurable more gain when they are almost vertical. Sloping radials have some other advantage: less birds. -- Wim PA3DJS Please remove abc first in case of PM |
Radials
Ian Jackson wrote:
In message , writes Ian Jackson wrote: In message , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. Yebbut ........ You've just said "the ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequency". I assumed that "ideal" = "best". Poor choice of words on my part. Most of the literature I've seen on the subject recommends radials about 5% longer than the driven element. I don't recall anyone saying why. All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. True - but what's the angle of the radials got to do with their length? Not a whole lot but they do interact. I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. I had presumed you had already do this (or something similar) in order to say that slightly longer than a 1/4 wavelength was ideal. However, I have always assumed that the steeper the angle of the radials, the more the groundplane becomes like a vertical halfwave dipole - and the lower becomes the angle of radiation. The angle of radiation in free space for a vertical dipole and a GP no matter what the radial droop are both 0 degrees. The thing that changes the angle of radiation is the antenna distance from ground in wavelengths. -- Jim Pennino |
Radials
Wimpie wrote:
El 02-04-14 20:25, Ian Jackson escribió: In message , writes Ian Jackson wrote: In message , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. Yebbut ........ You've just said "the ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequency". I assumed that "ideal" = "best". . All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. True - but what's the angle of the radials got to do with their length? I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. I had presumed you had already do this (or something similar) in order to say that slightly longer than a 1/4 wavelength was ideal. However, I have always assumed that the steeper the angle of the radials, the more the groundplane becomes like a vertical halfwave dipole - and the lower becomes the angle of radiation. You are right, very steep radials become the lower half of a half wave dipole as the currents do not cancel eachother and contribute to the field of the quarter wave monopole. The "ultimate" version is the sleeve dipole. Not really. When they are in the horizontal plane, the contribution to the total radiation pattern is very small, and the contribution from the radials is even zero for the vertically polarized component at zero elevation. The theoretical gain of a GP with horizontal radials, radials drooping 45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi. The "somewhat longer then 1/4 wavelength" I also noticed with radials connected to a coaxial braid to form a narrow band common mode choke. the choking effect (common mode insertion loss) is better when they are somewhat longer then 0.25lambda (depending in thickness). The effect of sloping angle on zero elevation gain is small, and you get hardly measurable more gain when they are almost vertical. Sloping radials have some other advantage: less birds. Changing the angle of the radials has little to no effect on elevation gain unless the radial ends are a very tiny fraction of a wavelength above ground. Elevation radiation angle is almost totally determined by the antenna height above ground. -- Jim Pennino |
Radials
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Radials
Ian Jackson wrote:
In message , writes The theoretical gain of a GP with horizontal radials, radials drooping 45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi. I would have thought that the 'ultimate' would be when the droop IS 90 degrees (ie essentially a sleeve dipole). With a droop of 90 degrees, is the gain slightly more than 3.67? You can't physically have a 90 degree droop. The radials would have to extend horizontally for some distance, then drop to 90 degrees. That is a different antenna. How come that you can have a 1/4 wave radiator groundplane type of antenna with a gain that is more than a halfwave dipole (2.15 dBi) -even if it is more-or-less a sleeve dipole? When the radial droop approaches 90 degrees it really isn't a GP antenna anymore, it is something else. -- Jim Pennino |
Radials
Ian Jackson wrote:
In message , writes Ian Jackson wrote: In message , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. Yebbut ........ You've just said "the ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequency". I assumed that "ideal" = "best". . All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. True - but what's the angle of the radials got to do with their length? I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. I had presumed you had already do this (or something similar) in order to say that slightly longer than a 1/4 wavelength was ideal. However, I have always assumed that the steeper the angle of the radials, the more the groundplane becomes like a vertical halfwave dipole - and the lower becomes the angle of radiation. OK, let's look at some numbers and see what is actually happening. First, design a GP for 28.3 Mhz, 1/2 inch 6061 aluminum tubing with all elements the same length and look at the element length, impedance and gain in free space. Then change the radial droop to 30 degrees and 45 degrees, retune for 28.3 and look at the numbers again. All lengths are free space wavelengths of the driven element. droop impedance gain length SWR 0 deg 23.6 Ohms 1.34 dBi .247884 lambda 2.12 30 deg 41.6 Ohms 1.83 dBi .238687 lambda 1.2 45 deg 49.1 Ohms 2.2 dBi .234493 lambda 1.02 OK, now repeat with the radials 5% longer than the driven element. droop impedance gain length SWR 0 deg 23.3 Ohms 1.29 dBi .245373 lambda 2.15 30 deg 41.3 Ohms 1.81 dBi .236106 lambda 1.18 45 deg 50.4 Ohms 2.19 dBi .232007 lambda 1.0011 From the above the best SWR occurs with radial 5% longer than the driven element and the droop at 45 degrees. This is also the point of maximum 50 Ohm bandwidth. I will leave it as an execise for the reader to get the demo EZNEC and view the bandwidth graphs. In all cases the elevation angle of maximum radiation is 0 degrees. Now let's come down from free space and put the longer radial version on a typical single story house roof mounted on a pole. The house peaks around here are about 13 feet and 10 foot TV masts are cheap, so let's mount the antenna at 23 feet, which is .662 lambda at 28.3 Mhz, and see what happens. Note than because we are now over real ground vertical lobes are formed. Again I will leave it as an exercise for the reader to get the demo EZNEC and view the graphs. droop impedance max gain length SWR 0 deg 22.6 Ohms 2.48 dBi @ 35 deg .245373 lambda 2.12 30 deg 43.4 Ohms 2.24 dBi @ 40 deg .236269 lambda 1.15 45 deg 51.1 Ohms 1.94 dBi @ 45 deg .231667 lambda 1.022 It should be noted that there is a large second lobe: 0 deg 1.09 dBi @ 12.5 deg 30 deg 1.37 dBi @ 12.5 deg 45 deg 1.66 dBi @ 12.5 deg So which antenna is "best" in the real world? I would go for 5% longer radials drooping at 45 degress. -- Jim Pennino |
Radials
El 02-04-14 22:32, escribió:
wrote: El 02-04-14 20:25, Ian Jackson escribió: In , writes Ian wrote: In , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. Yebbut ........ You've just said "the ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequency". I assumed that "ideal" = "best". . All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. True - but what's the angle of the radials got to do with their length? I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. I had presumed you had already do this (or something similar) in order to say that slightly longer than a 1/4 wavelength was ideal. However, I have always assumed that the steeper the angle of the radials, the more the groundplane becomes like a vertical halfwave dipole - and the lower becomes the angle of radiation. You are right, very steep radials become the lower half of a half wave dipole as the currents do not cancel eachother and contribute to the field of the quarter wave monopole. The "ultimate" version is the sleeve dipole. Not really. When they are in the horizontal plane, the contribution to the total radiation pattern is very small, and the contribution from the radials is even zero for the vertically polarized component at zero elevation. The theoretical gain of a GP with horizontal radials, radials drooping 45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi. You may check your simulations, as in free space you will not exceed the half wave dipole gain with near vertical radials (for the quarter wave version). A quarter wave monopole with near vertical radials has same current distribution as a vertical half wave dipole (use sum of current in all radials). Of course provided that you don't have significant common mode current in the mast or coaxial cable, as this may increase or decrease the free space gain. When extending both sloping radials and radiator you can get more gain, but you get significant increase in common mode current as the radial ground no longer act as a floating ground point, and the input impedance has a reactive part. The "somewhat longer then 1/4 wavelength" I also noticed with radials connected to a coaxial braid to form a narrow band common mode choke. the choking effect (common mode insertion loss) is better when they are somewhat longer then 0.25lambda (depending in thickness). The effect of sloping angle on zero elevation gain is small, and you get hardly measurable more gain when they are almost vertical. Sloping radials have some other advantage: less birds. Changing the angle of the radials has little to no effect on elevation gain unless the radial ends are a very tiny fraction of a wavelength above ground. I can't match this statement with your earlier gain figures, or did I misunderstand you. Elevation radiation angle is almost totally determined by the antenna height above ground. Agree, but now the number of variables increases as you need to take into account nearby ground conductivity and far away ground conductivity. -- Wim PA3DJS Please remove abc first in case of PM |
Radials
El 03-04-14 1:04, escribió:
Ian wrote: In , writes The theoretical gain of a GP with horizontal radials, radials drooping 45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi. I would have thought that the 'ultimate' would be when the droop IS 90 degrees (ie essentially a sleeve dipole). With a droop of 90 degrees, is the gain slightly more than 3.67? You can't physically have a 90 degree droop. The radials would have to extend horizontally for some distance, then drop to 90 degrees. This is the same as saying, you can't have a 90 degree radiator, as due to wind it will bend. You know that going horizontally a few inch and then 90 degrees down doesn't make big difference compared to 85 degrees sloping. You only may experience some length difference to get lowest common mode current in the mast or feeder. Both option will not give you more gain compared to a half wave dipole (free space). That is a different antenna. How come that you can have a 1/4 wave radiator groundplane type of antenna with a gain that is more than a halfwave dipole (2.15 dBi) -even if it is more-or-less a sleeve dipole? When the radial droop approaches 90 degrees it really isn't a GP antenna anymore, it is something else. Is this because of electrical operation (I doubt), or naming convention? -- Wim PA3DJS Please remove abc first in case of PM |
Radials
Wimpie wrote:
El 03-04-14 1:04, escribió: Ian wrote: In , writes The theoretical gain of a GP with horizontal radials, radials drooping 45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi. I would have thought that the 'ultimate' would be when the droop IS 90 degrees (ie essentially a sleeve dipole). With a droop of 90 degrees, is the gain slightly more than 3.67? You can't physically have a 90 degree droop. The radials would have to extend horizontally for some distance, then drop to 90 degrees. This is the same as saying, you can't have a 90 degree radiator, as due to wind it will bend. You know that going horizontally a few inch and then 90 degrees down doesn't make big difference compared to 85 degrees sloping. You only may experience some length difference to get lowest common mode current in the mast or feeder. Both option will not give you more gain compared to a half wave dipole (free space). If you do this you do not have a ground plane antenna; you have an asymmetric dipole with one skinny element and one fat element. That is a different antenna. How come that you can have a 1/4 wave radiator groundplane type of antenna with a gain that is more than a halfwave dipole (2.15 dBi) -even if it is more-or-less a sleeve dipole? When the radial droop approaches 90 degrees it really isn't a GP antenna anymore, it is something else. Is this because of electrical operation (I doubt), or naming convention? Actually both. BTW, in retrospect I don't think that 3.67 dbi number for 85 degrees is correct. The limiting gain should be that of a vertical dipole as you pointed out. I think the problem is that most analysis programs have issues with very close wires and very small angles. This can be seen by analyzing a fan dipole and decreasing the angle between the elements. Eventually the results stop making any sense. -- Jim Pennino |
Radials
Wimpie wrote:
El 02-04-14 22:32, escribió: wrote: El 02-04-14 20:25, Ian Jackson escribió: In , writes Ian wrote: In , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. Yebbut ........ You've just said "the ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequency". I assumed that "ideal" = "best". . All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. True - but what's the angle of the radials got to do with their length? I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. I had presumed you had already do this (or something similar) in order to say that slightly longer than a 1/4 wavelength was ideal. However, I have always assumed that the steeper the angle of the radials, the more the groundplane becomes like a vertical halfwave dipole - and the lower becomes the angle of radiation. You are right, very steep radials become the lower half of a half wave dipole as the currents do not cancel eachother and contribute to the field of the quarter wave monopole. The "ultimate" version is the sleeve dipole. Not really. When they are in the horizontal plane, the contribution to the total radiation pattern is very small, and the contribution from the radials is even zero for the vertically polarized component at zero elevation. The theoretical gain of a GP with horizontal radials, radials drooping 45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi. You may check your simulations, as in free space you will not exceed the half wave dipole gain with near vertical radials (for the quarter wave version). Addressed in another post. A quarter wave monopole with near vertical radials has same current distribution as a vertical half wave dipole (use sum of current in all radials). Of course provided that you don't have significant common mode current in the mast or coaxial cable, as this may increase or decrease the free space gain. In the simulation there is no mast or cable. When extending both sloping radials and radiator you can get more gain, but you get significant increase in common mode current as the radial ground no longer act as a floating ground point, and the input impedance has a reactive part. There is always a frequency where the reactive part is zero. See my long post comparing configurations. As the simulations have no cable, you can not see any common mode current effects. The "somewhat longer then 1/4 wavelength" I also noticed with radials connected to a coaxial braid to form a narrow band common mode choke. the choking effect (common mode insertion loss) is better when they are somewhat longer then 0.25lambda (depending in thickness). The effect of sloping angle on zero elevation gain is small, and you get hardly measurable more gain when they are almost vertical. Sloping radials have some other advantage: less birds. Changing the angle of the radials has little to no effect on elevation gain unless the radial ends are a very tiny fraction of a wavelength above ground. I can't match this statement with your earlier gain figures, or did I misunderstand you. See my long post comparing configurations. Elevation radiation angle is almost totally determined by the antenna height above ground. Agree, but now the number of variables increases as you need to take into account nearby ground conductivity and far away ground conductivity. Only if you want to simulate some particular and specific place. For the vast majority of problems you just use average ground values. EZNEC does allow you to change the ground values if you want to see what happens in someplace like a desert with poor ground. -- Jim Pennino |
Radials
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Radials
El 03-04-14 18:41, escribió:
wrote: El 02-04-14 22:32, escribió: wrote: El 02-04-14 20:25, Ian Jackson escribió: In , writes Ian wrote: In , writes The ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequencey. Why is this? I would have thought that a 1/4 wave would be best, as it offers the lowest impedance. First you have to define what "best" means. Yebbut ........ You've just said "the ideal radial length for ANY ground plane antenna is slightly longer than 1/4 wavelength, no matter for what frequency". I assumed that "ideal" = "best". . All antennas are a trade off for impedance, bandwidth, gain and in most cases physical ability to build the structure. Changing the radial length will have a small effect on impdedance and resonant point but changing the radial angle will have a bigger effect on impedance and a very small effect on resonant point. True - but what's the angle of the radials got to do with their length? I would suggest downloading the demo version of EZNEC and modeling a GP to see what small changes in various parameters do. I had presumed you had already do this (or something similar) in order to say that slightly longer than a 1/4 wavelength was ideal. However, I have always assumed that the steeper the angle of the radials, the more the groundplane becomes like a vertical halfwave dipole - and the lower becomes the angle of radiation. You are right, very steep radials become the lower half of a half wave dipole as the currents do not cancel eachother and contribute to the field of the quarter wave monopole. The "ultimate" version is the sleeve dipole. Not really. When they are in the horizontal plane, the contribution to the total radiation pattern is very small, and the contribution from the radials is even zero for the vertically polarized component at zero elevation. The theoretical gain of a GP with horizontal radials, radials drooping 45 degrees and and drooping 85 degrees is 1.42, 2.22, and 3.67 dbi. You may check your simulations, as in free space you will not exceed the half wave dipole gain with near vertical radials (for the quarter wave version). Addressed in another post. My results (IE3D, now Mentor Graphics Hyperlynx): Quarter wave radiator over 4 quarter wave radials, no sloping: impedance at resonance 23 Ohms, Gain at zero elevation: 1.52 dBi 0.625 wave radiator over 4 quarter wave radials, no sloping: Gain at zero elevation: 1.52 dBi, 2.29 dBi at 20 degr elevation. 0.5 wave radiator over 4 quarter wave radials, no sloping: Gain at zero elevation: 2.05 dBi. Quarter wave radiator over 4 quarter wave radials, 45 degrees sloping: Impedance at resonance 54 Ohms, gain at zero elevation: 1.97 dBi Quarter wave radiator over 4 quarter wave radials, 85 degrees sloping: Impedance at resonance 74 Ohms, gain at zero elevation: 2.14 dBi All in free space, without a mast. Adding a mast, especially for the sloping case can give large deviation depending on the CM impedance as seen from the floating ground. I did simulations and current measurements for my own mast, but the results cannot be applied to other configurations. As I stated before, the difference between the configurations is hardly measurable. Nice to see that the over-rated 5/8 lambda antenna doens't perform better then the quarter wave antenna (at low elevation angle). Though the design is more demanding, I prefer the half wave option as you can use less, sloping, shorter radials without running into common mode mast current problems. -- Wim PA3DJS Please remove abc first in case of PM |
Radials
Wimpie wrote:
snip My results (IE3D, now Mentor Graphics Hyperlynx): Quarter wave radiator over 4 quarter wave radials, no sloping: impedance at resonance 23 Ohms, Gain at zero elevation: 1.52 dBi 0.625 wave radiator over 4 quarter wave radials, no sloping: Gain at zero elevation: 1.52 dBi, 2.29 dBi at 20 degr elevation. And an impedance in the hundreds of Ohms. 0.5 wave radiator over 4 quarter wave radials, no sloping: Gain at zero elevation: 2.05 dBi. And an impedance of about 1,000 Ohms. Quarter wave radiator over 4 quarter wave radials, 45 degrees sloping: Impedance at resonance 54 Ohms, gain at zero elevation: 1.97 dBi Quarter wave radiator over 4 quarter wave radials, 85 degrees sloping: Impedance at resonance 74 Ohms, gain at zero elevation: 2.14 dBi All in free space, without a mast. Again, in free space the maximum is ALWAYS at zero elevation. Adding a mast, especially for the sloping case can give large deviation depending on the CM impedance as seen from the floating ground. I did simulations and current measurements for my own mast, but the results cannot be applied to other configurations. As I stated before, the difference between the configurations is hardly measurable. Nice to see that the over-rated 5/8 lambda antenna doens't perform better then the quarter wave antenna (at low elevation angle). I wouldn't call an impedance range of 20 Ohms to 1000 Ohms "hardly measurable". In real life you have to feed the thing. Though the design is more demanding, I prefer the half wave option as you can use less, sloping, shorter radials without running into common mode mast current problems. And requires some sort of feed arrangement to transform 1,000 Ohms into 50 Ohms. In my opinion, dealing with the added complexity of impedance matching, which is almost always narrow banded, is not worth a dB or two of gain. I think I will stick with 5% longer radials at 45 deg and some ferrite at the feed point. -- Jim Pennino |
Radials
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Radials
wrote in message ... Note than because we are now over real ground vertical lobes are formed. Again I will leave it as an exercise for the reader to get the demo EZNEC and view the graphs. droop impedance max gain length SWR 0 deg 22.6 Ohms 2.48 dBi @ 35 deg .245373 lambda 2.12 30 deg 43.4 Ohms 2.24 dBi @ 40 deg .236269 lambda 1.15 45 deg 51.1 Ohms 1.94 dBi @ 45 deg .231667 lambda 1.022 It should be noted that there is a large second lobe: 0 deg 1.09 dBi @ 12.5 deg 30 deg 1.37 dBi @ 12.5 deg 45 deg 1.66 dBi @ 12.5 deg So which antenna is "best" in the real world? I would go for 5% longer radials drooping at 45 degress. Now we are getting somewhere in the discussion. For simple antennas that can not be rotated unless one wants to talk to a certain distance, the antenna does not make much if any differance. You get 'gain' in one direction and 'loss' in another. Just match it to the coax and take what you get. There is no real gain in an antenna, just redirecting the power that is supplied to it. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com |
Radials
On Thursday, April 3, 2014 2:28:40 PM UTC-5, Wimpie wrote:
Again, in free space the maximum is ALWAYS at zero elevation. Except for the 5/8 lambda, as I mentioned. That's only because you used 1/4 WL radials, which is a very perverted design. Try it with 3/4 WL radials. That will give you close to your textbook gain. And for an even better pattern use sloping 5/8 WL radials, which will start approaching the gain of a dual 5/8 WL collinear. I've compared 1/4 wave GP's, 1/2 wave's with decoupling, and 5/8 GP's with 3/4 and 5/8 radials on 10m to distant local stations, which is a good test of low angle performance. The 5/8 was always the best antenna in the real world using low angle space wave paths 30-40 miles across town. And the 1/2 wave was better than the 1/4 GP. The only reason the poor 5/8's get a bad rap is because people insist on using 1/4 WL radials under them. That's a disaster, particularly if used on VHF/UHF where the pattern is really critical. |
Radials
Wimpie wrote:
El 03-04-14 20:54, escribió: wrote: snip My results (IE3D, now Mentor Graphics Hyperlynx): Quarter wave radiator over 4 quarter wave radials, no sloping: impedance at resonance 23 Ohms, Gain at zero elevation: 1.52 dBi 0.625 wave radiator over 4 quarter wave radials, no sloping: Gain at zero elevation: 1.52 dBi, 2.29 dBi at 20 degr elevation. And an impedance in the hundreds of Ohms. From my memory it was closer to 50 Ohms, but for the gain figures this isn't important. But it is if you want to attach the antenna to a real radio. 0.5 wave radiator over 4 quarter wave radials, no sloping: Gain at zero elevation: 2.05 dBi. And an impedance of about 1,000 Ohms. Depends strongly on thickness/lambda ratio, therefore I didnt mention the value, and it isn't important for the gain. But again, it is if you want to attach the antenna to a real radio. Quarter wave radiator over 4 quarter wave radials, 45 degrees sloping: Impedance at resonance 54 Ohms, gain at zero elevation: 1.97 dBi Quarter wave radiator over 4 quarter wave radials, 85 degrees sloping: Impedance at resonance 74 Ohms, gain at zero elevation: 2.14 dBi All in free space, without a mast. Again, in free space the maximum is ALWAYS at zero elevation. Except for the 5/8 lambda, as I mentioned. Yep, but it isn't a GP antenna which by definition has a radiator about 1/4 lambda. Adding a mast, especially for the sloping case can give large deviation depending on the CM impedance as seen from the floating ground. I did simulations and current measurements for my own mast, but the results cannot be applied to other configurations. As I stated before, the difference between the configurations is hardly measurable. Nice to see that the over-rated 5/8 lambda antenna doens't perform better then the quarter wave antenna (at low elevation angle). I wouldn't call an impedance range of 20 Ohms to 1000 Ohms "hardly measurable". In real life you have to feed the thing. We were discussing gain.... You may be discussing gain but I am discussing antenna systems which have gain, bandwidth and impedance and to be usefull have to be practical to build. Though the design is more demanding, I prefer the half wave option as you can use less, sloping, shorter radials without running into common mode mast current problems. And requires some sort of feed arrangement to transform 1,000 Ohms into 50 Ohms. In my opinion, dealing with the added complexity of impedance matching, which is almost always narrow banded, is not worth a dB or two of gain. I think I will stick with 5% longer radials at 45 deg and some ferrite at the feed point. What someone will use, depends on many factors (not only electrical ones). I have some experience with HV, and I know how to design these circuits without loosing useful bandwidth, so I prefer the half wave. I like racing and wood pigeons, but not on my antennas! In residential areas over here, generally people don't like to see lots of aluminum in the air. So for my situation it is not the less then 0.5 dB addditional gain over a classic 4 radial GP, but just the common mode issue together with visible apearance (I don't want 4 radials). Note that we have maximum 400WPEP in PA-land, that also makes it easier. In practicality, you will see little difference between 2, 3, or 4 radials. You will have common mode currents of some magnitude with ANY GP type antenna. You will be hard pressed to notice 1 dB difference in a typical amateur system. -- Jim Pennino |
Radials
Ralph Mowery wrote:
wrote in message ... Note than because we are now over real ground vertical lobes are formed. Again I will leave it as an exercise for the reader to get the demo EZNEC and view the graphs. droop impedance max gain length SWR 0 deg 22.6 Ohms 2.48 dBi @ 35 deg .245373 lambda 2.12 30 deg 43.4 Ohms 2.24 dBi @ 40 deg .236269 lambda 1.15 45 deg 51.1 Ohms 1.94 dBi @ 45 deg .231667 lambda 1.022 It should be noted that there is a large second lobe: 0 deg 1.09 dBi @ 12.5 deg 30 deg 1.37 dBi @ 12.5 deg 45 deg 1.66 dBi @ 12.5 deg So which antenna is "best" in the real world? I would go for 5% longer radials drooping at 45 degress. Now we are getting somewhere in the discussion. For simple antennas that can not be rotated unless one wants to talk to a certain distance, the antenna does not make much if any differance. You get 'gain' in one direction and 'loss' in another. Just match it to the coax and take what you get. There is no real gain in an antenna, just redirecting the power that is supplied to it. And there is no such thing as cold, just the absense of heat... -- Jim Pennino |
Radials
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Radials
El 04-04-14 2:35, escribió:
wrote: El 03-04-14 20:54, escribió: wrote: snip My results (IE3D, now Mentor Graphics Hyperlynx): Quarter wave radiator over 4 quarter wave radials, no sloping: impedance at resonance 23 Ohms, Gain at zero elevation: 1.52 dBi 0.625 wave radiator over 4 quarter wave radials, no sloping: Gain at zero elevation: 1.52 dBi, 2.29 dBi at 20 degr elevation. And an impedance in the hundreds of Ohms. From my memory it was closer to 50 Ohms, but for the gain figures this isn't important. But it is if you want to attach the antenna to a real radio. 0.5 wave radiator over 4 quarter wave radials, no sloping: Gain at zero elevation: 2.05 dBi. And an impedance of about 1,000 Ohms. Depends strongly on thickness/lambda ratio, therefore I didnt mention the value, and it isn't important for the gain. But again, it is if you want to attach the antenna to a real radio. Quarter wave radiator over 4 quarter wave radials, 45 degrees sloping: Impedance at resonance 54 Ohms, gain at zero elevation: 1.97 dBi Quarter wave radiator over 4 quarter wave radials, 85 degrees sloping: Impedance at resonance 74 Ohms, gain at zero elevation: 2.14 dBi All in free space, without a mast. Again, in free space the maximum is ALWAYS at zero elevation. Except for the 5/8 lambda, as I mentioned. Yep, but it isn't a GP antenna which by definition has a radiator about 1/4 lambda. I understand your reasoning, but do a google (image) search on "GPA antenna" and you we see that many people don't follow your convention. 5/8 and 1/2 WL are also included. It is not the name, but the operating princple that is of importance. Adding a mast, especially for the sloping case can give large deviation depending on the CM impedance as seen from the floating ground. I did simulations and current measurements for my own mast, but the results cannot be applied to other configurations. As I stated before, the difference between the configurations is hardly measurable. Nice to see that the over-rated 5/8 lambda antenna doens't perform better then the quarter wave antenna (at low elevation angle). I wouldn't call an impedance range of 20 Ohms to 1000 Ohms "hardly measurable". In real life you have to feed the thing. We were discussing gain.... You may be discussing gain but I am discussing antenna systems which have gain, bandwidth and impedance and to be usefull have to be practical to build. Though the design is more demanding, I prefer the half wave option as you can use less, sloping, shorter radials without running into common mode mast current problems. And requires some sort of feed arrangement to transform 1,000 Ohms into 50 Ohms. In my opinion, dealing with the added complexity of impedance matching, which is almost always narrow banded, is not worth a dB or two of gain. I think I will stick with 5% longer radials at 45 deg and some ferrite at the feed point. What someone will use, depends on many factors (not only electrical ones). I have some experience with HV, and I know how to design these circuits without loosing useful bandwidth, so I prefer the half wave. I like racing and wood pigeons, but not on my antennas! In residential areas over here, generally people don't like to see lots of aluminum in the air. So for my situation it is not the less then 0.5 dB addditional gain over a classic 4 radial GP, but just the common mode issue together with visible apearance (I don't want 4 radials). Note that we have maximum 400WPEP in PA-land, that also makes it easier. In practicality, you will see little difference between 2, 3, or 4 radials. You will have common mode currents of some magnitude with ANY GP type antenna. Clear, but by using a half wave radiator (end-fed) CM current is about 13 dB lower to start with, and that saves me a lot of aluminum that doesn't contribute to the radiation. Again, I know design/construction is more elaborate. You will be hard pressed to notice 1 dB difference in a typical amateur system. that was the reason I mentioned: "The effect of sloping angle on zero elevation gain is small, and you get hardly measurable more gain when they are almost vertical. Sloping radials have some other advantage: less birds." I still can't reproduce, or find a reliable reference for your 3.67 dbi for a quarter wave with quarter wave 85 degr sloping radials. We drifted away somewhat from Irv's posting.... -- Wim PA3DJS Please remove abc first in case of PM |
Radials
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Radials
On Friday, April 4, 2014 8:39:52 AM UTC-5, Wimpie wrote:
For zero elevation (relevant for line of sight comms in VHF and up), the gain will virtually not improve when using horizontal 3/4 WL radials. The horizontal radials don't contribute to the vertically polarized wave. Horizontal no.. Try them sloping. As far as I know, the only case where horizontal radials are preferred would be with the 5/8 radiator with 1/4 radials. In that case, they are better straight out than sloping. But if I remember right, all other cases will be better with sloping radials. And for an even better pattern use sloping 5/8 WL radials, which will start approaching the gain of a dual 5/8 WL collinear. Agree, that really helps! You have to take care of mast/feeder radiation that may distort the pattern (hence gain) significantly. Sure. But one should do that with any elevated vertical for the best performance. I've compared 1/4 wave GP's, 1/2 wave's with decoupling, and 5/8 GP's with 3/4 and 5/8 radials on 10m to distant local stations, which is a good test of low angle performance. The 5/8 was always the best antenna in the real world using low angle space wave paths 30-40 miles across town. Probably this was because of the added heigth for the 5/8 lambda radiator over a half or quarter wave, or you had (somewhat) sloping 5/8 WL radials. They were sloping. But... I remember that I started out with a 5/8 with 1/4 radials. It was also better than the 1/2 wave even with the theoretical problems.. It could have been due to the higher radiator, but not sure.. I'm not sure if an extra 5 feet in height would make that big a difference on a 30 mile local path when the base was a fixed 36 feet high in all cases. Could be, with the current distribution of the usual 5/8 wave element. |
Radials
On Friday, April 4, 2014 10:47:26 AM UTC-5, John S wrote:
On 4/3/2014 7:37 PM, wrote: I would appreciate a definition of gain as used in this thread. I have a hard time understanding how a passive device can supply gain. Thanks, John Most all real antennas have some gain over isotropic. |
Radials
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