[Antennas] ground mounted vertical radials question

Wed Nov 15 12:41:12 EST 2006

Thank you Saandy.
There are some very, very good articles written on radials that dateback to 
the 30s and there are other articles that are rather new that explain all of 
this very well, too. Just do a search on the Internet or check out the 
articles available through the ARRL. What I have read in the post is a mish 
mash of some good understanding and not-so-good understanding on the 
subject. And I am no expert, nor claim to be.
I am not sure who provided a summary earlier, but who ever it was did a fine 
job. It summaraized the subject very well.
1. More radials is almost always better.
2. Longer is almost always an improvement.
3. There is a diminishing return on length as well as number. This does 
not mean shorter is as good, it just means that quantity and length improve 
the situation in nearly every instance. Do in Internet search on this study 
from the 30s.
4. The diminishing return is similar to what you'd see in an exponential 
growth curve, but just the opposite. So, as you hit the somewhat magical 
number of 16, in most cases, the question becomes whether you should drop 
more radials when the help to your efficiency only increase marginally 
(meaning that the improvement is less and less for every additional radial). 
It then becomes a question of practicality. Going from 2 radials to 4 is 
excellent (doubling the number of radials). Going from 32 to 64 (doubling 
the number) will not see the same result in improvement. The return from 
your effort is less even though increasing the number of radials almost 
always helps. So, do you want to spend the time on that project, per se, 
when it does not achieve a large gain?
This is why the general rule of thumb is to drop down as many as you 
"practically" can and as long as you can, since very few hams have the time 
and energy to place down 120 radials a 1/4 wave length long, which is what 
the 1930s study concluded to be near a perfect ground and why, as it is my 
understanding, every AM broadcast station in the USA is mandated to this 
practice by the FCC.
Good hamming to all,
W8OKN
> ...guys, there's a big difference between a workable antenna and a GOOD
> antenna. A workable may get along with 2 radials per band, but it's hardly
> enough! You only get a reasonable SWR but a lot of losses too.
> If ground mounted, you need many radials to create a conductive mat under
> the antenna, not in order to realize a counterpoise. You guys tend to
> intermingle operation with radials with operation with a ground plane! 
> These
> are 2 different mechanisms!
> Antennas on ground planes don't rely actually on the length of the ground
> wires; they merely use them to provide the return path for the field 
> induced
> currents. Radials, on the other hand radiate: they are a part of the 
> antenna
> itself. This can be proven by playing with the slant angle of the radials:
> when spread in an horizontal plane the input impedance is 36 ohms as for a
> ground plane. When dropping vertically underneath the antenna, you get 72
> ohms, as in a dipole.
> Definitely something else: one is BASED on the "radials" being 0.25
> wavelengths and one who couldn't care less what length they are, as long 
> as
> the ground capacitance is enough and the gathering of the field induced
> current is reasonably good enough.
> Doctor, leave the poor mathematics alone, get physical. OBSERVE! There are
> too many variables for calculation: some areas cope very well with two
> radials, some need 100. You don't even have to calculate: think what will
> happen if you have a copper plate backyard!! I should do just that, since 
> I
> live over sand, here, in 4Zulu land!
> Just put in all you can and enjoy that: nobody can do more!
>>>> Alex Eban 4Z5KS
> alexeban at gmail.com
> 050-7774300
> 03-9067913
>>>>> -----Original Message-----
> From: antennas-bounces at mailman.qth.net
> [mailto:antennas-bounces at mailman.qth.net] On Behalf Of Charles Greene
> Sent: Wednesday, November 15, 2006 4:52 PM
> To: Dr. William J. Schmidt, II; David Ashworth; antennas at mailman.qth.net
> Subject: Re: [Antennas] ground mounted vertical radials question
>> Bill,
>> Who do you want me to quote, W2FMI or ON4UN?. What measure of
> evaluation? Increase of 0.2 dB in the far field? Why not 1.0 dB, or
> even 3 dB? Who is going to notice 1/2 an S unit, particular with QSB
> over 10 dB? As I don't want to get into a flaming contest, this
> will be my last communication on the subject.
>> I agree on this: add radials until the ground resistance essentially
> stops decreasing.
>> 73, Chas
>> At 11:54 PM 11/14/2006, Dr. William J. Schmidt, II wrote:
>><<Using more than 16 radials does not help much.>>
>>>>Prove this.... Show me mathematically how this makes any sense.
>>>>Sincerely,
>>>>Dr. William J. Schmidt, II K9HZ
>>Trustee of the North American QRO - Central Division Club - K9ZC
>>>>Email: bill at wjschmidt.com
>>WebPage: www.wjschmidt.com
>>>>"If you drink... don't drive. Don't even putt" - Dean Martin.
>>>>>>----- Original Message ----- From: "Charles Greene" <crgreene at cox.net>
>>To: "David Ashworth" <fathom at dslextreme.com>; <antennas at mailman.qth.net>
>>Sent: Tuesday, November 14, 2006 8:34 PM
>>Subject: Re: [Antennas] ground mounted vertical radials question
>>>>>>>David,
>>>>>>The best approach is to go for more radials on the order of 0.1
>>>wavelength rather than less radials that are longer. I have a
>>>Hustler 6BTV and I put 2 radials for each band about a 1/4 wave
>>>length each; however, that was several years ago and I'm smarter
>>>now. So if a radial is 0.1 wavelength on 80, it is 0.2 wavelength
>>>on 40, 0.4 wavelength on 20 and so on so it is an effective length
>>>on all bands. The reason for this is that current in the ground
>>>radial drops off over 0.1 wavelength so making the wire longer is
>>>not necessary, but the longer wire does not degrade the effect of
>>>the radial, so the longer wires are still an effective length. You
>>>would think 1/2 wavelength would not be a good length as it would
>>>ofer a high impedance at the antenna, but looking at the current
>>>that is not the case. Using more than 16 radials does not help
>>>much. In other words, 32 radials marginally better than 16, but
>>>not twice as good.
>>>>>>>>>73, Chas W1CG
>>>>>>At 12:37 AM 11/11/2006, David Ashworth wrote:
>>>>Hello to all. Will be installing a Hustler 5BTV vertical on the ground,
> up
>>>>in the country where there is no problem with people tripping over
> radials.
>>>>The radials will NOT be buried. They will be placed upon the ground.
> Been
>>>>reading my reference material on radials, but would like to hear from
>>>>operators that have been there/done that. The lowest band will be 80
> meters
>>>>and the highest 10 meters. Hustler recommends at least two radials per
>>>>band. Then, been reading W2FMI's book about short verticals. Think he
> was
>>>>happy with about 40 radials. Am I on the right track, the more radials,
> the
>>>>better, up to a certain point? The soil there is very dry unless it has
>>>>been raining. As soon as the sun comes out, there goes the moisture
> content
>>>>of the soil. So, would it be better to spread, say 40 radials at 1/8
>>>>wavelength, or maybe 20 at 1/4 wavelength? Would you spread some for
> just
>>>>80, or do a combination of the different bands? If this was salt water,
> bet
>>>>you could throw a coat hanger in there, but it is not. Any good ideas?
> I
>>>>am leaning towards less radials and longer radials, but experience is 
>>>>the
>>>>best teacher. Thank you for your comments/recommendations, Dave, NC6P.
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