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Author Topic: Radial lengths once and for all  (Read 5915 times)
WA5MTQ
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Posts: 14




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« on: March 12, 2012, 02:28:08 PM »

I have been a ham since 1976.  Unfortunately during that time I have seldom been able to put down roots Long enough to go the the expense of putting up any sort of commercial antenna.  I did have a commercially made cheap G5RV that the Texas summertime prairie winds massacred in about 3 months.

Although my lifestyle gave me little reason to consider a ground-mounted vertical, I recall that back in the 80s there was so much "cussing discussing" radial lengths.  One side insisted "bury 16 radials for each band with each said radial cut to 1/4 wave -- 4 band times 16 radials, you put down 64 tuned radials).  The other side vehemently held that "If its ground mounted just put down as many random length radials as you can; in other words, all that matters is that you get as much metal under the vertical as your property would allow.

Now, I am finally retired, well settled in my home on a large lot and want to put up a good commercial vertical.

And so the question (likely controversial as ever) to all you good hearted Elmers out there: (1) HOW MANY RADIALS DO I REASONABLY NEED; (2) SHOULD THEY BE TUNED TO 1/4 LENGTH OR JUST RANDOM LENGTH; (3) BEING AROUND HAM RADIO AS LONG AS I HAVE, WILL I BE BANISHED FROM EHAM JUST FOR ASKING WHAT MANY WILL VIEW AS JUST ANOTHER STUPID QUESTION ABOUT RADIALS?

Thanks beforehand to all who will answer.

Steve
WA5MTQ
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K3VAT
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Posts: 874




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« Reply #1 on: March 12, 2012, 02:45:35 PM »

...   And so the question (likely controversial as ever) to all you good hearted Elmers out there: (1) HOW MANY RADIALS DO I REASONABLY NEED; (2) SHOULD THEY BE TUNED TO 1/4 LENGTH OR JUST RANDOM LENGTH; (3) BEING AROUND HAM RADIO AS LONG AS I HAVE, WILL I BE BANISHED FROM EHAM JUST FOR ASKING WHAT MANY WILL VIEW AS JUST ANOTHER STUPID QUESTION ABOUT RADIALS?  Thanks beforehand to all who will answer.  Steve WA5MTQ


May I suggest that you first read a series of articles by Rudy Severns N6LP at http://www.antennasbyn6lf.com/.  I think that the vast majority of elmers posting here would agree that Rudy is a recognized talent in the field of antennas.

Also, see the website of Tom, W8JI http://w8ji.com/ where there are many valuable and informative discussions on antennas. Likewise, the above for Tom.

ON4UN's book, LowBand DX'ing (from the ARRL or Amazon) covers this subject in detail and is worth your $ if you're serious about vertical antenna (especially for the lowbands).

Finally, both CQ and QST Magazines have done articles on this exact question - you may be able to search their archives and view the full articles.

GL, 73, Rich, K3VAT
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G0GQK
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Posts: 634




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« Reply #2 on: March 12, 2012, 03:20:40 PM »

If the wires are buried under the surface it matters not how long they are as long as they are of a reasonable length. If you are considering a vertical using raised radials then the radials should be quarter waves resonant for the bands you intend to use.

Mel G0GQK
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N4NYY
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Posts: 5058




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« Reply #3 on: March 12, 2012, 05:03:29 PM »

If you are ground mounting, make about 20-30 radials that are longer then the height of the antenna. But it is not that crucial on the ground. Most people randomize ground mounts with 25-35ft lengths. That is likely to be bigger than the antenna.
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W0BTU
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« Reply #4 on: March 12, 2012, 09:30:27 PM »


http://www.w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html
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K9KJM
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« Reply #5 on: March 12, 2012, 09:51:38 PM »

The bottom line:    If you are installing ELEVATED radials (At least 7 or more feet above ground) You can "tune" them to length, (And get by with only a few- Four is considered good)

And as also already pointed out, If you are installing the radials in or on the ground, Do not bother to try to "tune" them- Changing soil conditions will detune them anyhow.   In or on the ground radials the standard advice is "As many as you can get in, And as long as possible" Seems like good advice to me.

Bare copper wire remains the best conductor to use, Commercial AM radio stations used #10 gauge soft copper wire, A good size for ham use is #12 gauge house wire (It is a simple matter to zip the insulation off with a handi knife) #14 gauge also works, But in the northland with the earth freeze/thaw cycles in some soils with lots of stones, Going with too small a wire gauge results in mechanical damage.
The wire gauge seems to have very little effect on RF performance.  (Super light gauge wire will also work just fine, (#22 gauge, etc)  Only problem with it is mechanical damage happens easily.
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K0ZN
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« Reply #6 on: March 12, 2012, 10:39:40 PM »

 Hi.

It is very, very simple:

(1.)  It is OHM's LAW !!  Copper wire conducts electricity (RF energy) MUCH better than plain old, dry, Texas dirt !! (or any other dirt !!)
(2.)  The radial system is, literally, the other HALF of your antenna. So, obviously, you want the best conductor you can get. (with in reason).

ALL that in-ground/on-the-ground radials do is improve conductivity and reduce ohmic losses in the ground system HALF of the antenna.
Consequently, the better the conductivity of the radial system the better the efficiency of the antenna SYSTEM. With a handful of radials
losses can approach 50%. With a modestly extensive radial system, they can pretty easily be reduced to less than 10%. It is pretty much
about how much energy, money and labor you want to put in to the ground system.

Many studies have been done over the years, and they all generally end up in the same general ball park. If you want a "perfect" ground system
(in or on ground radials), thus yielding about 99% radiation efficiency, you generally need a very large number of radials close to
a 1/4 wave long.....typically, 75 to 100.

If you are not a raving perfectionist and are willing to loose a few watts in ground losses (which, in the real world is pretty harmless) then you can
get by with fewer radials. i.e. if they can't hear you with 85 or 90 watts of effective radiated power, they are NOT going to hear you with 100!
You will get a lot of OPINIONS on how many radials are needed for "good" results. Fortunately, there are several good studies and modeling progams
out there that will give you pretty accurate numbers. You local soil type will also play into the equation.

My OPINION, based on articles read and results heard and experienced on the air over a lot of years kind of goes like this:  
"Good" starts at about 24 to 32 radials.
"Very Good" is about 32 to 50 radials.
"Excellent" is 50 to 80.
"Perfect" is 80 to 100.  
(the foregoing assume 1/4 wave length).

Actual length is not critical.  You CAN mix radial lengths and the system can be unsymetrical if real estate needs dictate.
The highest current/lowest voltage is right at the base of the antenna, so that is the most important place to REDUCE ground losses.
You are better off with a larger number of shorter radials than just a few long ones.

Very few hams go to the trouble to put in a truly extensive, large ground radial system so they don't have any true experience with the benefits of such. I have TWICE put
in radial systems of over 100 radials and the results very much justified the effort. My current 40 M antenna is a full size, 1/4 wave homebrew vertical over a radial system
of 103, thirty seven foot radials of AWG # 14 copper wire. The antenna is literally amazing at times. I rarely have to make more than one or two calls in even the worst
pileups in DX contests. The farther away the DX is, the more effective/competitive this antenna seems to become. i.e. as per theory, it does have a very low radiation angle and/or a lot of radiation at USEFUL angles.

Just keep in mind that verticals with good ground systems, while very effective transmitting antennas are, or can be, noisy on receive. Because of the low angle
radiation/reception, they can and do pick up power line and other man made noises and some type of horizontal receiving antenna can be helpful at times.
My personal experience has been that ground mounted verticals seem to start losing out to horizontal antennas above 20 M..... above 17 M for sure.  i.e.
you will have best results with a vertical from 20 M or lower.

Elevated radial systems and GROUND PLANE configurations can and do work well with a lot fewer radials. The problem is mechanical in terms of clearance issues.
If you can use/make an elevated system, I would strongly suggest doing a little research on the subject. The beauty of a ground mounted system is that it is "neat"
and out of the way from a mechanical point of view and the antenna is easy to get at and work on.....but it takes a lot more wire in the ground.

If you have a lot of wind or thunderstorms (high gusts), give some consideration to guying the antenna with a small diameter, non-conductive synthetic rope even if the manufacturer says guys are not needed. It is easy and cheap to do and adds a lot to the antenna's mechanical reliability.

   "YOUR results may vary........."  (due to local terrain, soil conductivity, urban vs. rural, size and number of buildings around the antenna, etc.)

73,  K0ZN




« Last Edit: March 12, 2012, 10:48:07 PM by K0ZN » Logged
W0BTU
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« Reply #7 on: March 13, 2012, 01:24:08 AM »

Testing by some very smart people has shown that it is completely unnecessary to use bare wire for radials stapled to the earth.

You can leave the insulation on, since it is the capacitance to ground (rather than the conductivity from the wires to the soil) that is really at work here. Removing the insulation makes little or no difference in your field strength at any distance from the antenna.

And if you bury them below the surface, don't go too deep. Depending on the soil conductivity, burying them more than ~3" actually reduces the efficiency of the antenna.
« Last Edit: March 13, 2012, 02:52:35 AM by W0BTU » Logged

N4CR
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Posts: 1757




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« Reply #8 on: March 13, 2012, 06:02:46 AM »

This power point presentation has some very good information about radial systems.

http://www.antennasbyn6lf.com/files/pacificon_2008.pps
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73 de N4CR, Phil

Never believe an atom. They make up everything.
KH6AQ
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Posts: 7718




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« Reply #9 on: March 13, 2012, 06:05:42 AM »

As K3VAT says see the radial papers by N6LF. The gist of the N6LF papers is:

1) For a full size vertical the radials need be no longer than 1/8 wavelength.
2) If using 1/4 wavelength radials DO NOT use fewer than eight or excessive loss (more than 1/8 wavelength radials) will be the result.

For that last one or two dB longer radials and more of them can be used. For example, I use 90 radials because I like to break through pileups.

My measurements on physically short loaded antennas is that for good performance the radials need be no longer than the vertical is tall.
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K0OD
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Posts: 3018




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« Reply #10 on: March 13, 2012, 07:24:13 AM »

Radial debate has been settled for decades and the copper manufacturers lost!

N6LF's meticulous and back-breaking research supports what Sevick wrote in QST in 1978. W8JI, has often posted here that large numbers of radials add almost nothing. And W8JI , who runs a full bore contest station likes breaking thru pileups too!

N6LF's research on asymmetrical radial fields, the kind most of us suburbanites have to use, does answer some common questions for the first time. But again we see that "perfection" just isn't necessary with reasonably large verticals.   


--
"Short ground-radial systems for short verticals", J. Sevick
    QST , Apr. 1978, pages 30-33
    An introduction to ground radial design for the radio amateur; includes a section on how to measure ground conductivity.
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K0ZN
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Posts: 1818




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« Reply #11 on: March 13, 2012, 05:42:59 PM »

 One could argue the "number of radials" issue to infinity....and there still would be some controversy.  That said:  I knew Dr.Sevic personally....had several
 eye-ball QSO's with him. (His passing was a true loss to ham radio.) Jerry NEVER said that a smaller, shorter radial system was BETTER than a more extensive radial system. What he addressed, as have others, is the issue of "marginal returns". I mentioned that in my previous post also. For an Amateur operator, the size/effort/expense is to a
fair extent a personal choice as to how far towards perfectionism one wants to go. (This is a HOBBY!) Just because someone elects to put in more radials than the next guy
doesn't mean they are making a mistake nor is there a guarantee they are wasting their time. Frequency, soil conductivity, terrain and conductors in the near and far field vary a lot between installations. I can't speak for what other people experience at their QTH. All I can say is that my personal experience and results with large "over kill" radial systems has been extremely good.

Although this is a subjective statement: I tend to think there is/was a reason all the Military, Commercial and Marine shore stations use large extensive radial systems
under antennas that benefit from them and I don't think it was because the design engineers had purchased stock in the copper wire companies.

From what I have seen, there are few cases where engineering the cheapest, easiest solution yields the best results unless cost is the PRIMARY design goal.

....again:  "YOUR results may vary."

73,  K0ZN
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W0BTU
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« Reply #12 on: March 13, 2012, 06:00:12 PM »

What I found interesting was how well Jerry Sevick's ~6' high vertical worked on 40 meters. With his huge capacity hat and a good ground system, he put out one heck of a signal.
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