ELEVATED RADIAL SAG

[flintstone mop]

Hello All,
Getting ready for some 160M experimentation. I am going to try 6 elevated radials 120 feet long. Looking at various sources it looks like a 45 degree angle. The end of the radial is 10 feet off the ground. I tried stretching out one and most of the radial sags and is touching the ground. Should I poke some sticks in the ground to try to maintain the elevated radial idea??
Looking in some archived Ham topics it seems that others just keep lifting the distant end until there's 1-2 feet between wire and ground in the middle of the sag.
TNX
FRED

[W4EWH]

I'm planning a vertical for 80 Meters, so I'm very interested in this as well.

AFAIK, the biggest worry with radials is that the poor conductivity of the ground will absorb enough signal to make an antenna ineffective: the question is "how close is too close? I'd be guessing if I said "at least six feet high", although there are other reasons for choosing that height as a minimum¹.

The first question then, is about electrical height. What's the minimum height for effective elevated radials?

W1AC

1. There are, of course, good reasons to elevate radials besides electrical ones:

• Low-hanging wire is a garrote for passing animals, such as deer
• Wires that are almost on the ground can cause tripping
• Unless they're in an isolated area, wires that are on  the ground are a hazard for lawnmowers, snowblowers, etc.

[K5UJ]

There's a height below which, they are not effective as "elevated" radials because they basically function as if they were lying on the ground.  The effective height is a fraction of wavelength (lambda).   I've seen figures of 0.1 lambda which on 160 would be around 50 feet.  There's a contester somewhere in Wisconsin with a 160 tower that has the feedpoint elevated and he's done that with the radials almost that high, or at that height.  I think if done that way, you only need four of them.

I bet you could achieve good results with a lower set of radials but nothing like 2 feet high.  That's essentially like laying them on the ground.  If you can get them up 20 feet that might be okay because as is often the case with antennas it is not a black and white situation--there is a gray area in there in which you will see some performance, just not as good as the 0.1 lambda high performance.   This is one of the reasons so many hams who set up ground systems for 160 simply buy a lot of wire and start burying or laying them on the ground. 

OTOH, maybe one of the guys who are antenna modeling whizes can find out how looooow you can gooooo 

Rob

[flintstone mop]

Interesting thoughts. I tried Google and not even any pictures to show the elevated radials. There was a sketch I saw online during the summer and it looked like the radials where at a 45 degree angle and the ends were 10 feet high. THat is when I tried the same here and discovered the sag.

Fred

[WD8BIL]

That's what I'd do,Fred. Just get some broomhandles or PVC or whatever looks like it'll work. If your experimenting ain't no need to turn into rocket science!

[w4bfs]

hi Fred ... still thinking about exotic south seas ? ... K4bp put up a 90 ft Rohn 45 tower with multiple beams ... he called me in to figure out how to use the thing on 160 .... using 4 elevated 1/4 wl radials at the 30 ft point and reverse feeding got a reasonable feedpoint Z ( 90 + j80 as I recall using the MFJ ant analyzer ) .... It gets out like a bomb ... usually works dx 1st call barefoot with rx signals s units better than dipoles ....its pretty cool ....wish I had one 73 John

[flintstone mop]

hi Fred ... still thinking about exotic south seas ? ... K4bp put up a 90 ft Rohn 45 tower with multiple beams ... he called me in to figure out how to use the thing on 160 .... using 4 elevated 1/4 wl radials at the 30 ft point and reverse feeding got a reasonable feedpoint Z ( 90 + j80 as I recall using the MFJ ant analyzer ) .... It gets out like a bomb ... usually works dx 1st call barefoot with rx signals s units better than dipoles ....its pretty cool ....wish I had one 73 John

WOW a BOMB!!! YES the South Seas are on my mind constantly. It was a sample of an easier life!!
I have read about the radials getting to those heights and would require a lot of tuning, I guess. I still need to see an installation/drawing or pics, similar to what you speak to be able to implement these radials and how to deploy them. Any of the B'cast engineers give a link to some pics,,,,I'm drawing blanks
Thanks
Fred

[w4bfs]

we tried 24 to 35 ft above showing only a small change all of the radials are insulated from the tower and tied together and then to coax center conductor ... the coax shield ties to the grounded tower ... no hairpins or trombone feeds ...this is why its called reverse feed ... the radials are mostly hortz with belly sag ... a small L network in the shack flattens the line nicely ...it werks

[k4kyv]

You might be interested in this. They advertise regularly in some of the broadcast rags.  Notice that the radials slope upwards from the base of the tower to a network of support poles. Sort of inverted radial sag.

The wires are attached to the ground rods at the base of the tower and by a ground strap to the ATU. Beyond this ground connection, the wires must be insulated throughout their length. Each wire is slightly more than a quarter-wave long. A turnbuckle and tensioning spring provide adequate tension to support the wires. The posts may be steel or wood, but the wires must be insulated from them because considerable RF voltage develops at their outer ends. Back-guys may be needed at the outermost posts. For strength, the wires are Copperweld, which, because they are made of steel with thin coating of copper have virtually no scrap value. And they are much less costly than pure copper wires. Pure copper wires would stretch under tension, but the Copperweld will not. There are wires up in the air, but they are high enough to allow vehicle traffic under them.  

http://www.nottltd.com/ElevatedRadialSystem.pdf

Here is a scanned version of a paper on the same topic, presented at the 49th Annual NAB Broadcast Engineering Conference in April of 1995 and published in the NAB 1995 Broadcast Engineering Conference Proceedings.
http://www.scribd.com/doc/34884702/New-AM-Broadcast-Antenna-Designs-Having-Field-Validated-Performance-by-Clarence-M-Beverage

Some more interesting titbits on the subject, referring largely to broadcast, not just Hammy Hambone antenna installations, so maybe less BS factor than one would expect from e-Ham, QRZ.com, or popular ham radio rags:

Abstract

Previous computer-modeling studies indicated that four elevated radials may be used in conjunction with an elevated vertical monopole (tower) to produce radiated field strength which is equivalent to that emitted by a similar monopole using 120 buried radials. Inquiries have been received concerning the effect of increasing the number of elevated radials, and/or changing the height of the radials above ground. Analysis shows that there seems to be an optimum number of elevated radials for each height and soil type. Surprisingly, the continued addition of more and more elevated radials eventually produces a reduction in performance. The computer code used for this work was NEC, a “method of moments” program developed at Lawrence Livermore National Laboratory

http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=486070

http://www.steppir.com/pdf/radial%20systems%20for%20vertical%20antennas.pdf

http://puhep1.princeton.edu/~mcdonald/examples/EM/belrose_icap97_1_14_97.pdf

Counterpoise? On the Use and Abuse of a Word

[KM1H]

All the recent studies (read ON4UN's book, etc) indicate that 8-12' is fine for 160.

The most important part of the radial is close in so get that area high ASAP. The feedpoint on my 160M pair is about 8' high and then I slant the radials up to the 12-15' range and run over tree branches. This was installed in 1990.

I couldnt do much in the way of commanding a frequency until I got to around 32 radials each and then I was in the top tier of cracking DX pileups. At a prior QTH with poor ground (all glacial sand) I had to go to 120 radials plus a ground screen of four 4' x 50' , 2x4" mesh welded, galvanized and plasticoated rabbit fencing. Connecting all that in took weeks of work and then I was finally able to crack those pileups. It was then I said "never again" to on ground radials.

Elevated radials perform best over poor ground and my hilltop rock pile certainly qualifies.

Carl
KM1H

[KM1H]

 

Analysis shows that there seems to be an optimum number of elevated radials for each height and soil type. Surprisingly, the continued addition of more and more elevated radials eventually produces a reduction in performance

I used the hammy hambone method as there was no antenna software available to mere mortals in 1990.

I started with 4 radials and recorded the feed point impedance and spent a few days operating. Then doubled the radials and repeated, etc. Each increase improved the DX workability and reduced the feed impedance. There was substantially less change between 16 to 32 so I figured any more effort wasnt worth the time. With close to 300 countries on 160 the results speak for themselves especially since I run only 1200W on a band with loads of QRO.

Carl

[k4kyv]

That is also true of buried radials in most normal soils.  Anything above 60 is probably overkill, and the  difference between 30 and 60 would be imperceptible at a distance.

I run 120 1/4λ buried radials following commercial broadcast practice. The soil is fairly good here, but I am prone to using overkill on everything.

[flintstone mop]

Thanks Don and Carl,
I am ready to go fer it. I can conjure something up that will make this play and experiment.
THanks guys the PDF made my day.
I'll get a hold of some plastic 10 foot conduit,,,got to think,,,,# 18 solid enamel wire hmmmm

Fred

[k4kyv]

Another perspective is to think of the radial system as a shield between the lossy earth and the radiating part of the vertical.  Completing the other half of the resonant antenna length is actually a separate matter, and the two issues ought not to be confused. A ground mounted half-wave vertical  with no radial system at all will indeed resonate and take a load perfectly, but the majority of the power will be wasted heating the earth. Old timers used to call them "worm warmers", a term that should still be right up there next to "cloud burner" in the lexicon of ham radio jargon.

At one extreme, if the radials are lying on the ground or buried slightly below the surface, the maximum number of radials is needed.  BTW, the radials would work more effectively lying on top of the surface than by burying them, since buried radials have a thin layer of lossy earth between the ground system and the  radiator.  But at the lower HF frequencies and MF frequencies the losses caused by a few inches of soil are inconsequential, so it is best to bury them slightly to protect them from surface traffic.

At the other extreme, such as a quarter-wave VHF, UHF or CB ground plane mounted tens of feet off the ground, only 3 or 4 radials are needed, and arguably, only two radials will suffice. In this case, the vertical radiator is far away from the  lossy earth, and there is little  need to shield it from the ground.  The ground plane indeed serves only to complete the resonant length; a half-wave vertical with no ground plane would work fine, if it could be isolated from its support pole.  I'm not sure about their present location in CO, but the old WWV transmitter site on the east coast used half-wave verticals mounted up and down the sides of wooden utility poles.

So, it logically follows that, as one goes from one extreme (buried, with many radials) to  the other (2, 3 or 4 radials elevated a substantial fraction of a wavelength), that at intermediate distances in between, the higher off the ground, the fewer the number of radials needed to effectively shield the radiator.

Also, it is said that adding a few buried radials to an existed elevated radial system or vice versa will increase the ground losses. This jibes with the IEEE report that there is an optimum number of elevated radials for a given height off the ground and soil conditions.

Maybe it's more a matter of semantics than a real engineering principle, but I included in the list of web pages W4RNL's essay on the "counterpoise" because I thought it might be interesting. I had never confused a buried radial system or wires leading from the base of the antenna to a ground rod with a counterpoise, but until I read his article it had never occurred to me that there might be a distinction between a counterpoise and an elevated radial system.

[WU2D]

I have been using elevated radials on 80M verticals and vertical arrays to good effect in my woods in the thick of the trees. I have them high enough that they are still over my head in deep snow. 4 or 5 radials work just fine - more would be better. The match to 50 Ohms with a 65 ft vertical wire pulled up into a tree and 65 ft radials at 10 feet off the ground is excellent. Mike WU2D

[Steve - WB3HUZ]

The match to 50 Ohms with a 65 ft vertical wire pulled up into a tree and 65 ft radials at 10 feet off the ground is excellent.

This likely indicates loss.

[K6JEK]

The series of articles by Rudy Stevens in QEX on experiments with radials seemed to show that elevated radials needn't be high at all.  There was 1 dB of difference between six inches and four feet. 

People will debate this forever, of course.  I was impressed by the methodology and care with which Stevens conducted his experiments.  It was a five part series.  Part 3. April 2009 shows the radial height experiments.

Good luck

[K5UJ]

Right.   6 inches; 4 feet, all basically tantamount to laying them on the ground.   Did this Rudy guy compare 6 inches or 4 feet with 25 or 30 feet? 

[WD8BIL]

Right.   6 inches; 4 feet, all basically tantamount to laying them on the ground.   Did this Rudy guy compare 6 inches or 4 feet with 25 or 30 feet?

On 160 meters?

[K6IC]

Jon,  K6JEK is correct about Rudy Severns' measurments and articles in QEX.  He presented his results at the Pacificon Hamjyvention in 2008 IIRC.  The QEX article is the  Nov/Dec 2009 issue.

Rudy, N6LF,  has a very nice Web site  where some or all of the info in the QEX article is included:
http://www.antennasbyn6lf.com/

I have an 80 M 1/4-wave vertical and a 160 M Inverted U,  both of which use few elevated radials.  Four for the 80,  and three for the 160.  These are about 8-feet off the ground for the 80,  and bout 15 feet for the 160.  the feedpoint Z of the 80 is abut 36 Ohms,  mildly reactive ... I forget the 160's Z.  These antennas work OK,  but I have no other Verticals with real ground screens to compare them with.

Elevated radials seem to work,  and at relatively low heights,  they do work for me.  But I have no real vertical with a "proper ground",  so I'm fat,  dumb,  and ...

Run what U got.   GL  Vic

[KM1H]

The match to 50 Ohms with a 65 ft vertical wire pulled up into a tree and 65 ft radials at 10 feet off the ground is excellent.

This likely indicates loss.

About 15 Ohms of loss. Bet it has good bandwidth also.

[KM1H]

Right.   6 inches; 4 feet, all basically tantamount to laying them on the ground.   Did this Rudy guy compare 6 inches or 4 feet with 25 or 30 feet? 

Ive read those articles when they came out and while they may work for his little patch of earth they should not be taken as gospel. His interest in working stations on 160 doesnt coincide with mine which is strictly DX. If I want to rag chew stateside I use the inverted vee.

I have an 80 M 1/4-wave vertical and a 160 M Inverted U,  both of which use few elevated radials.  Four for the 80,  and three for the 160.  These are about 8-feet off the ground for the 80,  and bout 15 feet for the 160.  the feedpoint Z of the 80 is abut 36 Ohms,  mildly reactive ... I forget the 160's Z.  These antennas work OK,  but I have no other Verticals with real ground screens to compare them with.

No offense intended but I find 36 Ohms hard to believe with only 4 radials.

[K6IC]

Guess that I should add:

BTW, my elevated radials are THHN building wire -- insulated.  The Fo of the antenna seems to be reduced a bit when rain drops are hanging on the radials.  And,  as the radials sag  over time,  the Fo is also reduced.  Because the radials are close to the ground,  it seems that the distance to the ground has a fairly large effect on the resonant frequency.

My approach has been to use the radial length to tune the vertical to the desired Fo--using  the vertical,  and adjusting the length of that radial to set the frequency,  and so on until all are adjusted to length.  Then connect all radials together.  When all radials are connected together,  the Fo does drop a bit.

Fred,  personally,  I use steel T fence posts driven into the ground,  with 1 1/2 inch PVC conduit slid over the post.  You can place a bolt through the PVC so set the height to the desired level.  Cut two V-notches at the top of the PVC,  and use 1/8 inch Dacron rope to fix the radial to the top of the PVC.  This allows you to control the sag.  This may not have a high acceptance factor of the XYL and so on.

Carl,  I was a bit surprised at the feedpoint Z,  BUT that is what I measured,  and the SWR seems to agree with that approximate value.  I make no claim of  being an antenna guru.  72  GL  Vic  ... Wish that there was a way to keep these wordy posts from jumping about ... almost impossible to edit them ...   VB

[K5UJ]

Vic, i went to Rudy's website but could not find anything on elevated radials.  probably didn't know where to look.  sorry; not to be difficult but if you could point me to the data he has on that i'd like to look at it.  tnx

73

rob

[K6IC]

Rob,

There are several references to elevated radial tests.  One is on page 23 of this link:
http://rudys.typepad.com/files/qex-ground-systems-part-6.pdf

Also some info here:
http://rudys.typepad.com/files/qex-ground-systems-part-3.pdf

I have not reread this series of articles -- just skimmed them.  If you have time,  it is nice to find all 7 QEX artcles on his site.  My first post implied that there was only one QEX article.  I attended his presentation at the hammy convention.  And so on.

73  Vic