Posted: 2/7/2014 2:31:47 PM EDT
| I have a vertical that covers 10, 15, 20, 40 and 75/80, I want to put out radials and the manual says two per band. I am going to add more, what is a happy length for the posted bands 50'? |
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The tuned, 2-per-band rule applies only to elevated radials (ie not in contact or buried in earth.)
For on-ground radials, more is better than less, longer is better than shorter. I think it's DX engineering that has a reprint of an ARRL article on radials, but is basically comes down to there's diminishing returns after 32 radials, and it really drops off after 64 or so. I have 32 24-foot radials on my 43' and do a pretty passable job as net control for the digital net with that. |
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Use 32 Radials Minimum in a ground mounted antenna. (any less than 32 your efficiency starts to drop)
--- Read the following: (I don't have love links for them so you will need to so some searches) -- "Ground Systems as a Factor in Antenna Efficiency" by Brown, Lewis & Epstein of RCA Labs, published in the June, 1937 issue of The Proceedings of the I.R.E. -- If you are an ARRL Member you can search the archives for the following articles by Jerry Sevick - W2FMI The Ground-Image Vertical Antenna - QST July 1971 The W2FMI Ground-Mounted Short Vertical - QST_March 1973 Short Ground-Radial Systems for Short Verticals - QST Aprl 1978 Or just get the book "The Short Vertical Antenna and Ground Radial" By Jerry Sevick W2FMI Here - |
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Mr Harry covered it, If your radials are in contact with the ground many are needed to counter act ground losses. I wouldn't make them any longer than about 5% longer than the antenna. If push comes to shove on space, many short radials are better than a few long ones as the field around the antenna is more dense up close. 73, Rob |
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Quoted:
For on-ground radials, ..., longer is better than shorter. not necessarily true. Depending on the number of radials and possible lengths, shorter radials of particular lengths may give up to nearly 6dB gain versus some longer lengths. I've posted a link before which really gets into the specifics of ground radials, see: http://www.ar15.com/forums/t_10_22/661247__ARCHIVED_THREAD____Finally_started_putting_in_radials_______.html&page=1#i11292636 http://www.ar15.com/forums/t_10_22/668727__ARCHIVED_THREAD____Vertical_antenna_height_vs_ground_radial_length.html&page=1#i11429992 Really depends on how much wire you want to put out and how long of radial lengths that can be accommodated. I think I commented once a hypothetical reasonable plan for a multiband vertical... something like say 4 (or 8) tuned radials for 80m, 8 for 40m, and 8 for 20m. Tuned lengths would be about 2/3 of the free space 1/4 wavelength based on the research in the article I link to. Radials in contact with the ground are much shorter than the free space length due to dielectric effect of the soil. |
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Ive noticed many pictures of HF Verticals attached to the side of a house. Obviously, you cant place radials around the base of the antenna where the house exists, and i always wondered how this affects the radial system?
I have a circumstance where i want to install a vertical at a location in my yard, but its close to a wall and a steep drop on one side? |
| My S9v43' vertical is placed at the rear of my yard against the 6' wooden privacy fence. Only 4 of the 20 radials I have go under the fence into the woods on the other side. Haven't noticed it making one bit of difference in the ability to make contacts in that direction. |
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Good question. N6LF did some experimental work on this question recently. In a nutshell, you will lose a little signal strength in the direction of the missing radials. How much you lose depends on a few things, but let's say it's anywhere from "you'll never notice it" to about 50% of your power.
It's best if you can get the antenna away from the house so you can get full-length radials 360 degrees around it (and reduce RFI inside the house). If you can't do that, at least try to move it away from the house enough that you can get some short radials down in the direction of the house. Failing that, put the antenna at the corner of the house so you can still have radials 270 degrees around the antenna. Ground Systems with Missing Sectors The steep drop on one side would require some modeling to determine the effect on signal strength. From what I've read, it's somewhere between "immeasurable" and "unnoticeable." Quoted:
Ive noticed many pictures of HF Verticals attached to the side of a house. Obviously, you cant place radials around the base of the antenna where the house exists, and i always wondered how this affects the radial system? I have a circumstance where i want to install a vertical at a location in my yard, but its close to a wall and a steep drop on one side? |