Elevated Radials

[flintstone mop]

Hi All
There was an interesting interview with a well known antenna manufacturer/Ham NOTT, In this months Radio World.  He was making a nice heavy duty version of the screw driver antenna.
The question came up about folded unipoles and raised ground radials. You start at the tower with a 30 degree angle and go upward so that a framer could run his equipment under the raised radials. NOTT said 6 is enough compared to the industry standard of 120 radials. The raised radials sould be a little longer than 1/4 wave. Does this sound ok?

Fred

[K1JJ]

Hi Fred,

Here's everything you ever wanted to know about ground radial systems, taken from my conversations with many 160M vertical gurus. I spent months testing and talking to these guys before writing this.

http://amfone.net/ECSound/K1JJ16.htm

Taken from this article he is what I said about elevated radials:

10) "The successful technique of using only 2-4 elevated radials may be overstated.

The jury is still out - many guys do not agree as to what amount of elevated radials equate to ground radials. According to some, four elevated radials on HF work fine . Still others say four have very little shielding effect and are down as much as 3-5 db over a full-blown 120 ground radial system. Four will work for a VHF ground plane that is essentially in free space, but for HF, the Earth is a major part of the equation and RF currents must be collected around the vertical in the near field and returned to the base in an efficient manner. A few elevated radials cannot do this efficiently simply due to the wide open missing gaps. Some say that at least 30 elevated radials are needed to do the job of 120 ground radials. Maybe more. Elevated radials 1/8 wave high or higher may be an exception to this.

My question is this:

 If 3-4 elevated radials are equivalent to an elaborate ground radial system, why do the AM broadcast stations continue to pour tens of thousands into elaborate 120 radial ground systems when they could hang four simple elevated wires? Why would the FCC still require it? Do the pros like to spend money for nothing or are the hams holding back a valuable secret? HA! Wish I had the answer. Either way, I have personally installed (90) 1/4 and 1/2 wave long in-ground radials under each of three in-line verticals here - I'm happy."

73,
T

[W7IXZ]

As a broadcast engineer at a 50 KW DA-2 station on 750, I have constructed several DA systems and in the past we were required to install 120 radials at each tower and bond them together to a copper strap where they cross each other.  Also we installed copper screen 50 to 60 feet diameter below each tower.  However in recent years there has been a lot of research into AM antennas and ground systems.  There is e "short" antenna called a "KINSTAR" made by Kintronic which is 67% reduction in height from a full quarter wave antenna that is FCC approved for Non-directional AM stations.  (see www.kintronics.com)  NOTT.LTD. has developed an ELEVATED radial system that is FCC approved and fully complies woth the FCC requirements for ground systmes at AM broadcast stations.  It has been proven equal to or better than a burried system and can be built out of copper weld instead of pure copper.  That makes the ground system less prone to theft (which happens a lot) and it lasts longer.  The ends are insulated and can be quite hot depending on the power.  So, if it is FCC approved for commercial AM installations, I would think it would be great for ham sue as well. (nott ltd website: nottltd.com or e-mail to: email@nottltd.com)

Larry W7IXZ

[K1JJ]

Hi Larry,

Do you know how many elevated radials they use to equate to the 120 buried?

T

[Steve - WB3HUZ]

Six (6)

[KB2WIG]

6  radials
6 meters
6 beers in a 6 pack

[K1JJ]

Six (6)

Hmmmmm... think so?

On 160M, at 1/4 wave away from the vert base the gap (using only six radials) is about 125' between radials.  120' * 2 *3.14 / 6 = 125'.   

With 120 radials it's about a  6' gap.

If you subscribe to the "shield/screen" theory to return RF current back to the vertical base, how does that wash?  The so-called gurus said the radial spokes need much closer spacing to collect the RF or it will have to flow through lossy Earth back... ??

T

[Steve - WB3HUZ]

Hmmmmm... think so?

Not me saying this, but Mr. Nott. Supposedly FCC approved.

[flintstone mop]

YUP the FCC approves his raised radial system for AM broadcast.
Fred

[K1JJ]

I wonder why it's only FCC approved for single stick systems... cud it be the pattern is not clean enuff for a multi-tower array?

Has anyone seen efficiency studies of an elevated six radial system compared to a 120 in-ground?  It's not easy to do on 160M or lower cuz the two towers will easily interact unless far far apart. According to what I read in the past, elevated with few radials was down 3-5 db from 120 gnd mounted.

I don't know the answer myself, so that's why I'm axing. The last time I went axing on the 160M reflector a few years ago, I got some private emails from guys saying they didn't want to post their response on the reflector for fear of getting attacked again. This debate has been raging for many years now....

T

[WU2D]

Tom,

I got a bug to do some DX on 75M in the "SSB DX Window" 3750 to 3800 kHz about 4 years ago. My goal was to work 100 countries in one winter season. My TX was an old Heath Marauder coupled to another classic, the Gonset GSB-201 which is an ancient 4/811 tabletop. I used the R-390A and TMC as the RX side. I used my inverted L until I ran out of patience - that was at about 40 countries.

What could I put up that would get my signal out further? The first thought was a Yagi facing east. I put up a full sized 80M dipole broadside to Europe with a reflector in back of it. The problem was that I only could get the beast up to around 40 feet. This system tuned well but it simply did not work.

Next I tried a vertical with a few ground radials. This worked OK, but it was not much better than the inverted L. I suspended four 65 foot radials at the 10 foot level and fed the vertical quarter wave at that height straight to 50 Ohm coax. Bingo - now I was hearing and getting DX better than the Inverted L and I quickly worked 10 more countries.

Being ignorant of what would happen, I figured that I would try an experiment. Why not add a vertical parasitic element 5% longer at around 50 feet off the rear radial and add three more radials around the parasitic?

The resulting beast was large but it was completely hidden in the woods.

Now I was giving the guys with the delta loops a run. This system allowed me to talk into Europe sometimes all day and the locals dissapeared. Of course the wjhole thing came down when I lost interest in DX.

Oh, I got up to 70 Countries before I quit that spring. Raised radials work on 80M, even in the trees.

Mike WU2D

 

[K1JJ]

Sounds like a neat experiment, Mike!

Yes, the parasitic vertical reflector is very effective. I used it myself as well as a few others.

No doubt a Yagi at 40' on 75M is about useless for DX. I wud pick the verticals over that without question.  I'm sure that elavated radials "work", but I still wonder how far down a vertical system like yours would be from a full blown set of 240 gnd radials for a pair of verticals like you described.

Unfortunately the only way to find out is to A/B them on the air with them far apart for no interaction. A 3-5db difference (if that's what it is) isn't easy to detect unless they are compared together.

I'm hoping to get my rigs and amps finished up before the end of the fall, so will be back on AM and the 75M DX window again. Maybe you'll get something up there again.  There's at least ten AMers I know who play around in the DX window with me from time to time.

Later -

T