The AM Forum

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

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.

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

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

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!

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

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

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.
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:

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 (http://www.antennex.com/shack/Dec06/cps.html)

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

 
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

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.

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

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.

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

This likely indicates loss.

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

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?

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

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

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.



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

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

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

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

Thanks Vic.  Well there's one NEC plot that seems to say that when radials are 5 meters above ground that results in 2.5 dB gain over having them on the ground.  The frequency was 7.2 MHz so 5 meters would be a significant height.  One thing I like about these papers is he actually built an antenna to use for tests instead of only doing modeling.

73

Rob

I like that part too Rob. I think TOM JJ has modeled and built and reported. I think someone else here.
It really helps us common folk out.
Fred

Unless I missed it, in those two articles, all measurements were done at 7.2 MHz and above.

That was my impression.  So you have to scale things to the low bands.    To possibly achieve the plotted performance from the data for the elevated radials 5 meters high on 40, you'd have to go to 10 meters high on 80 and 20 meters high on 160.  he's actually testing a bit higher than the 0.1 lambda fraction I gave at the beginning of the thread. 

My hunch is (assuming all radials are 1/4 w. long and the vertical is also 1/4 w.) there is a rough ratio relationship of height of radials and number of them that has to be maintained to achieve an acceptable gain figure, IOW 4 radials at 0.1 lambda and as you decrease height, the number of them has to increase at some number per meter of lost elevation until you are on the ground with 60 to 120 of them.

I'll report from the trenches what happens.
Better match?, known contacts previously made from the old design?, SSB contest in FEBRUARY!!!

I gots some 10 foot high plastic condit and a tulip planter on my battery drill and start stringing the radials. And fight the tuner at the base.

Fred

The world changes at 160 and lower, what that article says at 40M likely has no bearing.

Read thru the various BCB data of where stations replaced their rotting out buried radial fields with 10' or so high elevated radials and had to reduce power to conform to their original proof of performance. The FCC started allowing elevated radials a decade or so ago on an experimental basis and I believe they are now allowed as needed.

A Cristian broadcast AM transmitter site near Lincoln Park (South of Detroit) has an impressive nine tower sight with an elevated ground plane. The wire appears to be .375" stainless steel stretched as tight as a piano wire with very few supports. The elevation above ground is about 15 feet.

Mike

Impressive Mike,
Everything seems to point to get them high to avoid getting hung up in them. And 10 feet was a number from a broadcast antenna installation.

There were other links Don provided where some were 35 feet high and the feedpoint raised condsiderably also.

I'll try to start my adventure this weekend.

Fred

PICS coming tomorrow. Hopefully I remember to take them before we go to darkness.

I have 3 up so far and much easier to install than ground mounted. Effectiveness will be checked this Winter.

Thanks or tuning in.
Fred

OK with the USA time change madness I will post a pic sometime this weekend of the finished project. It would take special photo technique to see the magnet wire I used. #18 AWG

Easy to install and changed characteristics of antenna drastically......MA160 Cushcraft top loaded,capacity hat,30 feet tall.
At least the SWR is reasonable 2:1, 10kc BW and single digit reactance.
The Rx signals are as quiet as the dipole. Usual drop in sig level going to Vertical. close in stations would be lower RX sigs.............more listening and more use is needed to evaluate this new system.
All of those 10 foot high poles look weird out there. I hope the deer don't get tangled
FRED

Hello all, and long time no been here :) (Great grammar)

I can report some semi-interesting results from doing a vertical here, too.

I had 4 radials mounted at the ground level.  Remote tuna located at feedpoint, and 100 feet of wire in an Inv-L config....  40 feet (running parallel to the 40 foot tower) and then cutting off at diag level to a point about 20 feet off the ground.

I could get a decent match anywhere (Using a HULL electronics remote marine tuna), had RFI in the shack problems (the antenna was 15-20 feet away), but couldn't work anyone...  Maybe 10 contacts in 2 days....  6 meters seemed to work well with it as well.

Spoke with a friend who works 75 AM here on the west coast, he mentioned elevating them as high as I could get...  I figured I'd use the roof :)  So, I'm about 10 feet off the ground on my radials now.

Worked almost 60 countries in the next week, 30++ over CQWW.  Matching is a LOT different now, sometimes the best I can do is 1.7-1.9.  Antenna is slightly better than a dummy load above 21 mhz....  I've worked some 15 meters and some 2 meters, but nothing compared to when on the 11 meter vertical at 40 feet....  I even broke a couple pileups, I was surprised.

'Got my name called' on 20 AM once.  14 watts of carrier, not bad.

I'm going to increase it to 8 radials next, I have to get some poles to lift some of the ends up.  Radials all cut for 80 meter resonance now, I forget the exact length, but in the upper 60 foot range.  I also increased the length when possible a couple feet to couple them to the poultry netting that covers my fence (fences approximately an acre).

--Shane
KD6VXI

Dont expect the SWR to improve with more radials, just the radiating efficiency. A 1/4 wave vertical with no loss is around 26 Ohms so with a few more radials you should be at the 2:1 point.

Yep, elevated radials really do work.

Carl (and others).

I have an idea for a vert....  I picked up an 80 foot tower and have a 31 foot aluminum monopole I was going to mount on top of it and then feed it as a base fed vert.

BUT, that was before playing with the elevated radials.  I did a bit of reading, but came to nothing conclusive on this, so:

Can I run the radial network 10 feet up the tower?  If so, would be it better to ground the base of the tower, or leave it isolated electrically?

I also HAVE to run guy wires...  I was reading about people feeding towers as verts that some isolate the guy wires, break them up, etc., while others use them as capacitive hats....  Since their would be a "stinger" above the tower, would it be better to isolate and separate them, or use them as cap hats?

I guess another 'issue' would be power handling capabilities.  I'm not looking to do anything near the mobile, but you know I LIKE QRO....  Which would be the best method of feeding with 'available' components (like 4CX5000).

--Shane
KD6VXI


* Don't mean to hijack the thread, but one question led to another to another :) *

Finally unveiling of the elevated radials at MOP radio.
I'll see what happens with this antenna this Winter.
I found out that with about 150PF in series that 40M is ready to go. Almost entire band.
Thanks for looking.

Picture 005 was supposed to be a view of a radial leaving the ground rod heading to the first 10 foot pole about 20 feet away.

Im trying to show the general layout of the poles. The magnet wire #18 is too small to see with the camera. I'm not a very good photographer.

Fred

 
Will that be an insulated or grounded base?  With an insulated base you can slope the radials up fast and then run horizontal but putting down a ground screen as Ive mentioned a few times will probably help.

With a shunt feed you can use any point to establish a ground reference.




Id ground it for lightning protection and static bleed.


I
At a prior QTH I had 90' of tower with 4 el for 10/15/20 stacked on top. Guys were Phillystran which suck. The large amount of top loading resonated the tower down around 1700 KHz and required a big cap to tune out the reactance, I needed 1/4" spacing to keep from arcing with 1200W and the bandwith was only around 35-50 KHz. Luckily I soon moved to here and went with the elevated radials phased verticals sloping off the tower guys for 160.  You can easily do a 4 square on 75 with your proposed setup.



If it needs a tuning network then youre into a big vacuum and tubing coils. If its just a phased array its simple to do just with coax and each antenna only takes part of the power. I never bothered with those fancy phasing boxes, the F/B was only 15-20dB but I use Beverages to receive most of the time anyway.

Carl

The little vertical that could............proving to be a performer on 160M. I'll try      some A-B comparisons with my full length dipole / VEE at 70 feet.
 Some surprises that it's the Cushcraft 27 foot top loaded vert for 160M.
Fred

I don't have a choice on the grounded or not, it HAS to be grounded because of ice issues:  If I insulate it, then 3-4 months out of the year a good 15 days each of those months, it's unusable because it will be shorted.  Ice forces it.  I lost a 300 dollar ground plane antenna today due to ice, nice reminder.

I'm with you on the static bleed and lightening safety.  Although I've not had a strike here, near me, or anywhere I can find (other than Google earth lol), I DO have an issue with static electricity here....  It's the high desert.

I had tried a commercial ground plane.  It came down in the ice today.  SO, I'm back to doing things KISS.

You answered my main question:  Can I have the base of the tower GROUNDED, but also have my ground plane ELEVATED.  And the answer is yes.

Should prove to be interesting the v/i relationships below the ground screen / above the actual ground....

Thanks for the info..  I knew it would be necessary to go to vac caps and large diameter tubing....   It's going to be fun playing this far down low :)

The remote tuna is working great, but the noise is through the ROOF today, ground plane wire is +14 ga....  And it's measured at 3/8 inch about 2 hours ago in thickness in the vertical plane.  That's a buncha ice buildup!  The sag is pretty good, too, but the antennas still workin!

--Shane
KD6VXI