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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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