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[Articles Home]  [Add Article]  

Radials - How Many? How Long?

W2OE (W2OE) on October 31, 2001
View comments about this article!


I have been chasing DX on the low bands for more than 15 years and using vertical antennas for most of that time. I graduated from 1 vertical to 2 verticals to 4 verticals and always with the same question: How many radials do I need and how long should they be? The quick answer is certainly the more the better and the longer the better. However, there does appear to be a point of diminishing returns and there appears to be an optimal way to use a fixed amount of wire.

The following is based on hundreds of hours of laying down radials, conventional wisdom and only antidotal evidence but I am convinced it is sound.

  1. The distance between your radials at their outer most tips should be 0.05 wavelengths or less. Let's take a look at what this would mean on 80 meters. A full wavelength at 3.8 MHz is 984/3.8 or 258.9 feet. Lets round that up to 260 feet. 260*.05 = 13 feet. Assuming that our radials are a quarter wavelength long then each radial is 65 feet long and the circumference of the circle covered by our radials is 2*pi*65 or 2*3.1416*65 or 408 feet. In order for the outer most tips of our radials to be 13 feet apart we need 408/13 or 31 radials. Adding more quarter wavelength radials will result in only marginal improvement. However, if you can make your radials a half wavelength long then you can continue to see significant improvement as you add radials up to about 62. The circumference of this circle is 816 feet and 816/13 is 62. Conversely if your radials are only 1/8 wavelength you will see little improvement beyond 15 or 16 radials. Does this mean the shorter the radials the fewer you need? Of course not, but it does mean the shorter the radials the fewer you can use efficiently. The longer the radials the more you can use efficiently and the more the better.

  1. Point 1 assumes that our primary constraint is the length of the radial. With the cost of wire the constraint may well be the total amount of wire you have. Question now becomes for a fixed amount of wire what is the trade off between radial length and radial number for the most efficiency. With a little algebraic manipulation of the above concept we can derive the following formula:

RL = SQRT (TL/(40*pi*WL))*WL

Where RL = the radial length in feet; TL = the total amount of wire we have in feet; and WL = a wavelength in feet at the frequency we are interested in.

Lets take the above 80 meter example and assume we have 1000 feet of wire to work with - TL = 1000.

1000/(40*3.1416*260) = 0.0306.

The square root of 0.0306 is 0.1749.

0.1749*260 = 45.48.

So our radial length (RL) should be 45 feet and dividing 1000 by 45 gives us 22 radials. The most efficient use of 1000 feet of wire, at 3.8 MHz, is to divide it into 22 radials each 45 feet long. Let's verify that this gives us radials whose outer most tips are .05 wavelengths apart. We have already determined that a wavelength at 3.8 MHz is 260 feet and that .05*260 is 13. If our radials are 45 feet long the circumference of the circle covered by the radials is 2*pi*45 or 282 feet. Dividing 282 by 22 we get 12.8 feet between the tips of our radials or essentially the 13 feet we were looking for.

Our quick answer still stands - the more the better and the longer the better. In addition the longer the radials the more radials you can use efficiently. However, for a given radial length there is a point beyond which you are pretty much wasting your time; and for a given amount of wire there is an optimal way to use it.

Member Comments:
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Radials - How Many? How Long?  
by N2MR on October 31, 2001 Mail this to a friend!
Thanks Merv, that was very interesting, and since you have used many verticals you are talking from experience. Where does the .05 wavelength "rule of thumb" come from?
Mark N2MR
 
Radials - How Many? How Long?  
by W3GEO on October 31, 2001 Mail this to a friend!
This is the first time I have seen the .05 rule of thumb. Quite interesting. Also, I have seen some research that suggests the length of radials do not need to be any longer than the physical length of the vertical radiator. If one is using a full size quarter wave 65' vertical for 80 meters, then there is nothing to be gained by making the radials longer than 65'. On the other hand, it one is using a shortened loaded radiator of say 25' for 75 meters, then nothing is to be gained by making the radials longer than 25'. Any truth to this?


73
George
W3GEO
 
Radials - How Many? How Long?  
by WB2WIK on October 31, 2001 Mail this to a friend!
I never knock success, but in reading the article it seems that you're discussing ground-mounted verticals and radials, in which case I've never found any applicable algorithm for radial length. (With elevated verticals and elevated radial systems, yes, I have.)

1/2-wavelength radials are highly undesirable when elevated, since they reflect their termination impedance (nearly infinity) back to the antenna base and effectively "disappear" from the circuit. Since your article discusses both 1/4-wave and 1/2-wave radials, I have to assume you mean radials laying on, near, or beneath the ground. Buried radials, obviously, are much less critical to length since anywhere along their length, including at their tips, the impedance to earth is low.

Do you have any empirical data (F/S measurements, etc) that indicate tuning ground radials actually makes any difference? It would be interesting to see. I've never been able to tell any difference with ground-installed radials, on, say, a 40m 1/4-wave vertical, whether the radials were 20' long (arbitrary, non-resonant length) or 32' long (1/4-wavelength), and trust me, I've tried this many times at a variety of locations.

Let us know more!

73 de Steve WB2WIK/6

 
RE: Radials - How Many? How Long?  
by WA4DOU on October 31, 2001 Mail this to a friend!
The answers to these and many other questions about radials and their numbers/lengths are to be found in several different vertical antenna manuals. Among the good ones are Capt. Paul Lee's book and W6SAI's. I've used 5/8th wave verticals on 20 meters before and seen the direct benefit of Fifty 100' radials and one hundred 50' radials. Some research suggests that the 5/8th wave vertical benefits from 3/4 wave radials but all research on radials suggests that the additional length can't benefit the operation of the vertical unless there are sufficient numbers of radials, many more than a casual 16 or 24. Low angles of radiation are benefited by long radials and large numbers.
W2FMI's research with "shortened" verticals was that they required full sized highly efficient radial systems if they were to approach a high degree of efficiency.
The sign on the speed shop wall said, "speed costs money, how fast do you want to go?" The same applies here! If you have the acreage and the money, you can build the largest radials system ever devised by man. And rule the band(s).
 
RE: Radials - How Many? How Long?  
by W0JX on October 31, 2001 Mail this to a friend!
This issue has been covered extensively on the TopBand Reflector. The consensus seems to be that a separation of .025 wavelength at the radial ends is about optimum
or around 14 feet on 160.
 
Radials - How Many? How Long?  
by K2WH on November 1, 2001 Mail this to a friend!
I recently built and installed a 65' 80 meter vertical with on the ground radials. I currently have (40) 65' radials on the ground and the antenna works wonderfully. In my opinion, I would gain little more by adding more radials. Anyone with a disenting opinion on this?

K2WH
 
Radials - How Many? How Long?  
by K2WH on November 1, 2001 Mail this to a friend!
By the way, my radials are #22 gauge enameled magnet wire. It comes in up to 5000 foot rolls and only costs about $ 15.00. So, cost should not be a factor in putting down radials and as many as you want.

 
Radials - How Many? How Long?  
by VE4HST on November 1, 2001 Mail this to a friend!
Could spmeone please explain why the folks who make the Gap Challenger Vertical recommend just three radials, while Bencher who makes the HF6V Butternut recommends at least 24 or more radials for a ground mount. From what I have read, fellow Hams either tell you that one or the other is a garbage antenna. While others clain it is the best antenna that they ever used. My question is: Who is correct or are they both correct dependding on the antenna???? I am in the market for my first vertical and really dont know which one to buy???? Someone help PLEASE!!!!!

73's
Harry
VE4HST

PS The more Ham's you talk to the more confused you get???????????
 
RE: Radials - How Many? How Long?  
by WB2WIK on November 1, 2001 Mail this to a friend!
K2WH: I agree with you, except when using #22 magnet wire for radials be careful not to trip on them, walk on them, etc -- they break! I've used #19 gauge (I think) welding wire of unknown precise composition, available surplus for about $10 per 10,000 foot roll, and it's worked wonderfully for "temporary" (contest weekend) installations.

VE4HST: The Gap Challenger is a center-fed antenna, not base-fed like the Butternut HF6V. The three "radials" used at its base are for end-loading the lower end of the antenna to get it to resonate, along with a fixed capacitor installed near its upper tip, on 80 meters. They are not radials in the pure sense. The HF6V is a base-fed antenna which is a quarter wave, or three-quarter waves, or somesuch equivalently low-impedance, on all bands. It actually needs radials, they don't just help resonate the antenna, they ARE half the antenna. With the Gap, that's not the case.

73 de Steve WB2WIK/6

 
Radials - How Many? How Long?  
by N2LH on November 1, 2001 Mail this to a friend!
Great article and replies back. I have my few cents worth to add. I have been using for the past 2 winters and 30' home brew vertical. Using a 6' dia top hat of 1/8 alum crossed with #12 wire making a circle. Its base loaded with a #8 gauge coil (L(6") to D(3") = 2:1)and a small matching coil which bring the impedance from abt 28 ohms to 50 ohms. The bandwidth (2:1) is abt 150Khz. OK, so now abt my radial system. I have a small backyard so, I put out approx 50 radials, made from salvaging various lengths of data cable and stiping off the outer covering giving me lots of #24 stranded insulated wire. Where I could, I ran 16 radials close to 50'. others were about 25', and the remaining close to the edge of a neighbors yard about 12'.I used 4" pieces of coat bent in half to staple the end of each radial into the ground. There is a good chart which says how many radials for a given length of wire. The charts can be found in many Vertical antenna books such as one of my favorites by John ON4UN. In short, the rule of thumb that I agree with is, more is better, longer, even better. The only problem with shortened verticals that I have found, is they don't hear as well as they play. Cheers and see you all in the window. 73's..Larry.
 
Radials - How Many? How Long?  
by VE7VIE on November 1, 2001 Mail this to a friend!
Does this apply to HALF-WAVE verticals, and if so, how?
(I keep gettting conflicting opinions about whether 1/2 waves require (or benefit from) radials AT ALL.)

VE7VIE/KD7IGX
 
Radials - How Many? How Long?  
by K8DXX on November 2, 2001 Mail this to a friend!
I've always had a dream about someday having phased verticals (a four square) for 40, 80 and perhaps even 160. I would probably use ComTex equipment for the phasing. I was also thinking (here's the radial part) of just connecting quarter wave pieces of copper screen as my radials. What do you think about that idea?
 
Radials - How Many? How Long?  
by W8LOV on November 2, 2001 Mail this to a friend!
I have very limited space in my condo and would like to put up a ground mounted trap vertical, like the Hustler 6BTV. My space for radials is very limited and is somewhat long (20 feet) and narrow (9 feet) Also, due to concrete and fences, it is only practical to use four or possibly six radials. 20 meters is my band of choice. If I use four radials they could each be 8.6 feet long (20 meters at 1/8th wavelength), or I could use two at 8.6 feet opposite each other and the other two at 17.2 (20 meters at 1/4 wavelength) opposite each other. The other option is to go without any radials at all or some other approach I havenít yet thought of. If you had this awful QTH, what would you do?????? HELP!
 
RE: Radials - How Many? How Long?  
by WA4DOU on November 2, 2001 Mail this to a friend!
Half wave verticals don't require radials to "resonate" the antenna as its naturally resonant. However the radiation efficiency still depends on radials as does the low angle build up of radiation. There is no excaping this with 1/4, 1/2 and 5/8th wave verticals.
I once had a Swan vertical mounted on the ground on the patio of a "townhouse apt." in Charlotte,N.C. My patio was very small, however I used many short "clip on" radials on the patio, so as to be able to remove them when the patio was in use. Worked lots of 20 meter Long Path DX in the mornings with 100 watts out. In any given situation, use whatever length radials you can muster up and use as many of them as you can do. The results are worth it. At least they are in my opinion. Mediocre radial systems, mediocre results. But, even mediocre results are better than none.
 
RE: Radials - How Many? How Long?  
by WB2WIK on November 2, 2001 Mail this to a friend!
W8LOV: In your situation, I would not use the Hustler vertical, you have inadequate space for radials that make that antenna really sing.

I would recommend, instead, you consider the Sigma-5 from Force-12. There is a 20-17-15-12-10m Sigma-5 version which is only about 10' tall and requires NO radials, and actually works very well, I just tried one last weekend. Very impressive. Tiny footprint. No radials. Easy to hide. Very efficient.

http://www.force12inc.com/sigma5info-002.htm

73 de Steve WB2WIK/6
 
Radials - How Many? How Long?  
by W3JJH on November 2, 2001 Mail this to a friend!
Standard practice for AM Broadcast antennas is to use 120 1/4-wave radials per tower. That works out to a roughly 0.025-wave tip-to-tip spacing. In practice the will usually be less than 0.5-dB difference in the radiated fields from an antenna with 60 radials and 120 radials. Of course, the difference between a 3-radial system and a 120-radial system is only 3 dB (1/2 S-unit).
 
RE: Radials - How Many? How Long?  
by NZ5L on November 2, 2001 Mail this to a friend!
As I recall from my San Marcos (Texas) visit to Don Newcomb (the man behind Butternut vertical antennas) he used no radials but a ground plane of about 8 large steel plates welded together around the base of the antenna, as the greatest ground losses are in the near field. Whatever works. Personally, I like the no-radial types, such as GAP Titan, but the difference over a standard vertical with a basic system of 8 multi-band radials is probably miniscule in practical terms. I think the best way to achieve greater efficiency is to increase the radiation resistance by going to a 5/8 wavelength element,inverted L style. 165' is close to 5/16 on 160, 5/8 on 80, and 5/4 on 40 and can be matched with a simple L net. With this setup, 8 random (30-50') radials seems to get out just fine.
 
Radials - How Many? How Long?  
by G3RZP on November 5, 2001 Mail this to a friend!
If you can

a) measure no current in all the radials at the feed point

AND

b) going from no radials to 4 radials (one at a time) produces no measurable change in the antenna feed impedance

AND

c) you find you can work pretty well all you can hear on 80 and 160 with your vertical without radials

Question: are the radials doing anything for you?
 
Radials - How Many? How Long?  
by W2OE on November 5, 2001 Mail this to a friend!
As the author of the original article I would like to respond to a few of the comments:

Rule Of Thumb
The .05 wavelength rule of thumb comes from a lot of old timers, mostly topbanders. Some say that the tips should be no more than .025 wavelengths apart and this is infact what I have done on my 4square. However after going from 32 1/4 wave radials to 64 I can see no appreciable difference. There was an appreciable difference in going from 4 to 8 to 16 to 32.

Radial Length
Increasing the length of the radials improves the lower angles of radiation. If you are on the east coast working Europe on 75 meters you will probably see no improvement in going from 1/4 wavelength to 1 wavelength radials. However, you will probably see a marked improvement in working into the Pacific. SM6EHY compared east coast to west coast US signals on 10 MHz using 1/4 wave radials and then with 1 wavelength radials. After adding the 1 wavelength radials he felt that the west coast stations picked up 6 db on the east coast stations. (You can see his article at http://home.swipnet.se/~w-67089/EHYradials.htm.)


Elevated
More than 10 years ago Al Christman (I don't know his call) published an article in which he suggested that 4 elevated radials were the equivalent of 100 on the ground radials. There seems to have been somewhat of a religious war over this ever since. Lots of people use elevated radials and they work. Mine are on the ground a they work. The modeling software indicates that Christman is right, however, I know of no definitive study in which actual measurements were done.


Matching
Finally, the purpose of radials is NOT to match the antenna. You can get a pretty good match just by driving a 6 foot rod in the ground. Radials will provide this match too, but their purpose is to provide a return path along ground with minimal loss.

Regards, Merv
 
RE: Radials - How Many? How Long?  
by WB2WIK on November 5, 2001 Mail this to a friend!
Merv,

Re: elevated, quantity, rad angle

Simple test I ran at home, and would be simple for most, is to use continuously broadcast signals on 30m and 40m, which for me happen to be "close" (WWV, Boulder, CO, at 1000 miles on 30m) and "farther" (CHU, Ottawa, Quebec, at 3000 miles on 40m).

On my elevated vertical (base height 8m above ground), I added and subtracted radials by simply climbing the little roof tower and clipping them on, or off, as the case may be, using large alligator clips. In the case of the 1000 mi signal from WWV on 10 MHz, the signal stops improving at 4 radials. I tried 8-12-16, no difference at all on received signal at any time of day.

In the case of the 3000 mi signal from CHU on 7335 kHz, ditto. Signal improved dramatically from "no" radials to 4 radials, but then stopped improving.

The radials in my case are all 1/4-wave and sloping about 30 degrees below horizon to the corners of the roof, with string leads to hooks.

Just an "FYI" which seems to agree with the theory that 4 elevated, resonant radials are enough.

WB2WIK/6
 
RE: Radials - How Many? How Long?  
by N4RNM on November 5, 2001 Mail this to a friend!
Radials? How about a nearly perfect conductor extending miles in 180 degrees of the compass? I have a quarter-wave (32ft.) 40m vertical mounted on Hobie Cat sailboat pontoons floating in front of my antenna-restricted townhouse that is nothing short of amazing. I use it on 6m-160m with astounding results. I vote for the more metal in the ground, (or saltwater), the better. BTW, the one post that indicated losses were greater near the base of the antenna is correct--check out the size of the ground screens near the base of AM broadcast antennae--you will find them as big as practical with the copper strap that the radials are silver-soldered to on the perimeter. Thanks to all for the enjoyable reading.

Pix of the antenna are on page 19 of October QST.

73,
de N4RNM
 
Radials - How Many? How Long?  
by N0CGF on November 6, 2001 Mail this to a friend!
At a Hamfest I picked up some old QST mags. In that
pile the July 1971 issue had a article "The Ground -
Image Verical Antenna" by Jerry Sevick W2FMI. In this
very interesting article it listed the above Question,
with the Expeimental Results, the test equipment used
and on-the-air checks. There were also graphs and
tables of the test measurements made to come to the
answers to the above questions. To keep this short
read this article for his experimental results for
the answer to this questions.....There was also a good article about verticals in the March 1973 issue of
QST 73's Dennis
 
RE: Radials - How Many? How Long?  
by KA5S on November 8, 2001 Mail this to a friend!
I agree with the other comments on your query. Hustler BTV antennas really need a good ground. I used a 4BTV years ago from Central Texas -- no ground to speak of, just laterite and limestone -- and it didn't wake up unitl I hit about 24 radials. This was on teh ground, and a lossy one, at that. Being elevated will help you, but the condo location is a bad one for induced RFI. Each radial actually radiates, so anything it runs near will be subject to an RF field. That's properly speaking another thread.

[[Aside:

If you have the money - they aren't cheap - the Force 12 system mentioned looks like a very nice way to go. Or build your own! But for finding out what works, why not just duct-tape a 16 foot fishing pole to the rail and operate? Seriously! Quarter wave wire, and radials as you can make 'em. Add a tuner at the feedpoint for multiband operation (arguably not _much_ less efficicent with this setup on 20-10 than traps).]]

Cheers,

Cortland, KA5S

 
RE: Radials - How Many? How Long?  
by W4QCF on November 9, 2001 Mail this to a friend!
You are right on about that July 1971 QST issue with the article "The Ground -
Image Vertical Antenna" by Dr. Jerry Sevick W2FMI....was extremely important but there was still another study which I just found with a simply search on his name quote: "His April 1978 QST article on short ground-radial systems now serves as the world's standard for earth conductivity measurements."unquote...
If I remember correctly, the key was getting your DC ground resistance down to around 30 ohms(or less?) if I recall correctly; his research, with the results of actual tests, showed that you could get it way down with just short radials, e.g. 8-15' ...with even as few as 30-40 taking it way down..his research was published in several ARRL handbooks and/or antenna manuals, not to mention his work on baluns which was in many QSTs.
 
Radials - How Many? How Long?  
by AC5DK on November 9, 2001 Mail this to a friend!
Gee, I pounded a four foot 2" diameter pole into the ground and mounted my 6 BTV to it like the booklet said. I get 5/9 all the time on 40 & 30 meters and been accussed of running a kilowatt... DX is not a problem. Guess I'm blessed with good soil... Who knew?
 
RE: Radials - How Many? How Long?  
by AC4GT on November 10, 2001 Mail this to a friend!

I do not have a lot of personal experience with the verticles for ham radio...i have used about all the wires and have loved a lot of them....I do have a 38 foot 80 mtr verticle up and almost three years now and it is almost ground mounter and I can tell you that without radials but a good ground it does not work for beans......AC4GT
 
Hustler 6BTV Radial Pattern  
by N3QQD on November 14, 2001 Mail this to a friend!
Great article! Ok so I just bought a Hustler 6BTV and have a small backyard and can't put in 20+ ft. radials all over. If I can only make due with radials of various lengths up to about 10 ft or so will this help at all? Any recommendations on lengths I should use for this situation?

Thanks...
 
Radials - How Many? How Long?  
by GW3YDX on November 18, 2001 Mail this to a friend!
I feel that W2OE's suggestions are too prescriptive.

1. Carefully measuring a quarter-wave radial to bury it forgets two things. First, if it is plastic wire, it will be loaded and resonant at a lower frequency than if bare wire. Second, this precise measurement is hokum anyway, since the radial will be detuned when it is adjacent to ground, let alone buried in it!

2. The current flowing into earth below a vertical will be at a maximum below the vertical. That's where we want to put our grounding effort. If I had just 500 ft of wire and wanted a radial system on 80m, I'd use 25 - 20 ft radials, not 7 "magic length" 66 foot ones!
I recall a friend in the suburbs of London who had a garden 16ft by 20ft. He was a big DXer on 160 because his garden was virtually copperised. No long radials there.

If there is any useful input I can give, I can say that I have made comparisons of a 80m vertical with a full-sized delta-loop, adding radials in instalments and testing the difference. There was much improvement between 4 and 8 radials. Less improvement from 8 to 16. Marginal improvement between 16 and 32. I left it at 32. Note well - the radials were between 40 and 80 ft long, some of them bent. And it was on a good clay soil with a high water table. On sandy soil it would have been a different story

73 Ron, GW3YDX

 
Radials - How Many? How Long?  
by W2OE on November 18, 2001 Mail this to a friend!
Ron, apparently my article leaves much to be desired in terms of clarity.
First there was never any intent (and as far as I know no mention) of
measuring radials to a quarter wave length. Likewise there was no intent or
mention of the radials being resonant or loaded. Quite the contrary, I find
no value in attempting to make radials that are either buried or on the
ground resonant.

Secondly, I have no idea where you came up with the 7 66 foot radials. The
formula which I propose would indicate 15 32 foot radials, and there is
nothing magical or resonant about the length. It simply suggests that 500
feet of wire would be most efficiently used as 15 32 foot radials.
 
6BTV Installation Questions, Radials, Coax, Guying  
by KV4GX on December 26, 2007 Mail this to a friend!
Itís good to know that the small diameter magnetic wire will work for the ground mounted 6BTV radials.
I now wonder why anybody would spend $50 for a radial plate when small gauge copper wire can be so easily soldered together in a ring at the base; maybe that is for elevated mounting?
Is the tilt base worth the cost?
Which coax would you suggest for the full power limit and where is the best place to purchase it?
Is there any special rope you might recommend for guying?
 
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