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Author Topic: Amount of radials for Verticals  (Read 9666 times)
KD4SBY
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« on: November 29, 2012, 06:33:25 AM »

There have been many discussions on radials for ground mounted verticals, but I have an other question in that regard. Everybody knows that the more radials the better, but what are the penalties of having just a few, like eight of them of varying length? Living in a HOA I have very little real estate to begin with, and the rules have forced me to mount my 4BTV in the backyard 6ft away from my house. That leaves only half a circle of ground for the radials. Besides that, my backyard is only 15ft deep, not much for any length of radials. I have been operating with this antenna with mixed success, sometimes I do well, other times very poorly. (I can hear stations, they do not hear me with 100W - Ant. is tuned with analyser for low SWR) Can it be the amount of radials the reason? Comments anyone?
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N3OX
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« Reply #1 on: November 29, 2012, 06:47:53 AM »

I have been operating with this antenna with mixed success, sometimes I do well, other times very poorly. (I can hear stations, they do not hear me with 100W - Ant. is tuned with analyser for low SWR) Can it be the amount of radials the reason?

Could be.  You'll probably do better with a couple dozen than you will with 8.  Whether or not it's enough depends on a lot of factors, and whether or not it's your problem won't be clear until you try adding more.  Don't worry about how long they are, just go from the base of the vertical until you hit an edge of your area.  A probably good way to do radials in small irregular spaces is to mark out equal spacing of the tips around the edge and then run radials from the base to those points.  That way you end up with more of an even density. 

For a small area you could even consider making or buying a wire mesh.  Unforutnately it might be that poor results are due to the proximity of the house, or it could just be other factors that are keeping you from making the contacts you want.  But with only eight radials of varying length in a small area, I would certainly try to improve the ground system.

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
HB9PJT
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« Reply #2 on: November 29, 2012, 06:51:22 AM »

For elevated radials 2 pcs. are enough. 2 pcs. per band. Or in total 2 pcs. but then you have to tune them for every band.

But in your case an antenna without the need of radials would probably be the better choice. I would go with a Hygain AV-620 or AV-640.

73, Peter - HB9PJT
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K1WJ
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Posts: 454




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« Reply #3 on: November 29, 2012, 07:10:10 AM »

You should be able to adjust antenna so no tuner is needed. Put as many radials as you can, based on data I've seen, 16 ground radials would be the minimum I would shoot far. Space them out the best you can 360. Length of radials on the ground is not critical, when I laid out my 32 ground radials on my 4BTV I used lengths of 8,16 & 33ft. Make sure to have coax choke close to antenna feed point. Bottom line: do what you can do & make the contacts you can, the band conditions will be the major factor here. I also modified the antenna for operation on 12m & 17m with 1/4w vertical wires - real easy to do - works good. 73 K1WJ David
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W8JX
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« Reply #4 on: November 29, 2012, 07:41:40 AM »

Length of radials on the ground is not critical

Actually it does not even really matter. You can use any length you can fit in.
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W5FYI
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« Reply #5 on: November 29, 2012, 07:56:32 AM »

Here's what I did for a flagpole vertical in a small yard; I used insulated AWG18 wire, ran it straight out to the house, did a 90° or so bend, went out two feet or so, then straight back to the radial ring. Then back out to two feet from where its last bend was, did another 90° turn, then back to the ring, and so on until I had gone completely around the yard. Of course, at the radial ring I stripped the insulation and soldered each pass-through. When done, I sealed each solder junction with fingernail polish, then RTV silicone, and buried everything about an inch or so underground. In other words, the radial field is made of one continuous strand of #18 wire (I didn't cut the ends).

The ARRL Antenna Book lists a table that purports to give optimum radial numbers and lengths for anywhere from 16 radials up to 120. If you have the real estate to lay 120 radials at least 0.4 wavelength long, it will deliver the most power to the antenna. If you can stand a 3dB loss, then 16 radials 0.1 wavelengths long will suffice. It also says, "Using radials considerably longer...while not adverse to performance, does not yield significant improvement either," and "...the more total wire installed, the better the performance...."

Have fun.
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K0BT
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« Reply #6 on: November 29, 2012, 08:20:35 AM »

N6LF provided empirical information on this subject in a series of articles in QEX.  You can find the information at: http://www.antennasbyn6lf.com/design_of_radial_ground_systems/ under the heading "Series of QEX articles on ground system experiments".

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ONAIR
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« Reply #7 on: November 29, 2012, 12:45:43 PM »

Can one use buried aluminum foil or a section of chain link fence instead of regular radials?  Just wondering.
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W8JX
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« Reply #8 on: November 29, 2012, 02:32:38 PM »

Can one use buried aluminum foil or a section of chain link fence instead of regular radials?  Just wondering.

Chain link does not have a good bond through sections but field fence or chicken wire would work. Aluminum foil even if you could bond to it would not last long in soil if damp.
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KK5J
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« Reply #9 on: November 29, 2012, 05:01:28 PM »

You might look for LB Cebic's work on vertical performance with short radials. I think he published that in QST back in late 70's or early 80's if I remember correctly. He used a large number of short radials with his vertical with some success. I suspect it would probably be similar to a having a good wire mesh. Agree 100% with N3OX and others, you may have other performance factors you'll have to live with. Good luck.
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VE3FMC
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« Reply #10 on: November 29, 2012, 05:32:07 PM »

Here's what I did for a flagpole vertical in a small yard; I used insulated AWG18 wire, ran it straight out to the house, did a 90° or so bend, went out two feet or so, then straight back to the radial ring. Then back out to two feet from where its last bend was, did another 90° turn, then back to the ring, and so on until I had gone completely around the yard. Of course, at the radial ring I stripped the insulation and soldered each pass-through. When done, I sealed each solder junction with fingernail polish, then RTV silicone, and buried everything about an inch or so underground. In other words, the radial field is made of one continuous strand of #18 wire (I didn't cut the ends).

The ARRL Antenna Book lists a table that purports to give optimum radial numbers and lengths for anywhere from 16 radials up to 120. If you have the real estate to lay 120 radials at least 0.4 wavelength long, it will deliver the most power to the antenna. If you can stand a 3dB loss, then 16 radials 0.1 wavelengths long will suffice. It also says, "Using radials considerably longer...while not adverse to performance, does not yield significant improvement either," and "...the more total wire installed, the better the performance...."

Have fun.

I know a guy who has a Screwdriver set up like you have your vertical set up. One big loop of wire around the fence line in his back yard. He tells me that antenna works quite well, even on 160 with that setup. If I recall he told me he had about 250 feet of wire in his loop and it is just buried underneath the surface.
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K2DC
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« Reply #11 on: November 30, 2012, 03:57:09 AM »

, "Using radials considerably longer...while not adverse to performance, does not yield significant improvement either," and "...the more total wire installed, the better the performance...."

Have fun.

Brian Edward N2MF also published an extensive modeling study in QST sometime on the '70s that reached a similar set of conclusions:

-  The obviously biggest benefit comes from something vs. nothing.  Eight radials of 1/8 wavelength long was a large improvement over no radials.

-  There was some improvement over that from using 16 radials 1/4 wavelength long.

-  Beyond that, there is a diminishing rate of return from more or longer radials.  It certainly won't hurt, but you have to dedide if its worth the copper and the effort.

The bottom line is to do what you can and take what you get.

73,

Don, K2DC
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KB3HG
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Posts: 404




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« Reply #12 on: November 30, 2012, 07:13:24 AM »

Another way to look at a very limited space for radials. Think mobile HF. A few radials is like a small car. Many are like a big beast. All things being equal the beast will have better efficiency than the small car.  The ground plane is liken to a mirror, small mirror small reflection, a larger mirror a a bigger reflection.  Do what you can, a compromised antenna is better than no antenna. Do it and have fun.

Tom Kb3hg
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W5LZ
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Posts: 477




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« Reply #13 on: November 30, 2012, 10:38:32 AM »

Lets go back to that original post for a second.  'Tuned for the lowest/best SWR?', really?  Okay, but that's just half of tuning an antenna, and not the most important part anyway.  A dummy load has a fantastic SWR but makes for a terrible antenna with ot without radials...
 - 'Doc
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N8YB
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« Reply #14 on: November 30, 2012, 01:28:10 PM »

N6LF provided empirical information on this subject in a series of articles in QEX.  You can find the information at: http://www.antennasbyn6lf.com/design_of_radial_ground_systems/ under the heading "Series of QEX articles on ground system experiments".



This should be required reading for anyone considering installing a vertical antenna.
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