[PVRCNC] Optimum # radials article

Wed Nov 12 18:13:23 EST 2008

W8JI is one of those who measures.  And he's not some kind of autocrat rich celebrity we "common men" of common resources can now dismiss because of his dastardly autocratic money-bags celebrity-ness as nothing he's done could possibly scale down to our ordinariness.

Far from it.  He keeps up a large web site where he shares what he has.  He has an email address.  Ask him what you want to know.  He's been a great resource to a lot of hams.

He's had the opportunity to try all kinds of stuff on 160, including the only ham I know who put up a 160 dipole up at 300 feet to see how well  it would compare against a ¼ wave vertical over dense radials for DX. Models tell you all day long that broadside the dipole should be better by 3db or even more, depending. His description of the dipole (admittedly my recollection) was that it was rarely equal and mostly worse than the vertical.  Clearly something going on the models don't know about.

The comparison you quote is from a MODEL run.  The flaw in the model comparison is not from what happens in the air, but is in the evaluation of what happens from radials ON THE GROUND.

As to trying a solution, knock yourself out.  But do we want to export that to others as the way to go based on absolute specifications from a model based on the one thing that the model writers themselves say is imprecise?

From: Kent Winrich [mailto:kwinrich at gmail.com]
Sent: Wednesday, November 12, 2008 2:17 PM
To: Guy Olinger
Cc: Brian Alsop; PVRCNC
Subject: Re: [PVRCNC] Optimum # radials article

No doubt that running NEC is a pain in the backside.  Personally I have difficulty in working with the ground systems in those programs.  IMHO a lot of the models are not that reliable when trying to model ground systems.

W8JI may have done some testing, but where did he do the testing? Different times of year?  What was the comparison?   I can argue with his results, as my antennas are different than his.  I am not one of the "pro" stations.  I am an average ham station (heh below average actually).

Those that can run 120 radials per tower..... knock yourself out.  I dont know about you, but I dont have the room nor the resources to put in 120 radials.  If I could yes I would run a full ground plane.  Please do notice that the comparison was at up to 35 radials.  How many of us have more than that?  The big guns, like W8JI, but I bet the rest of us dont.  Again W8JI was comparing 60 radials.  The charts provided dont even go that high.

I am presenting this as an option for us smaller guys.  And to concentrate on the area around the base of the antenna.   I mentioned in PVRC, is this group strictly for the big guns?  If so, I guess I am in the wrong group.

A good point you brought up is "There remains, still, some number of poorly understood phenomena regarding the behavior of dirt at RF".  HOW TRUE!  How do you suggest that we better understand this phenomena?  By just relying on W8JIs tests?  Or perhaps by trying out our own situations?

Yes there is more measuring that needs to be done.  But that is what Ham radio is all about.  So go ahead and go with the W8JI situation.. if you have a four square.. and 40,000' of copper laying around.

On the other hand, I am going to build a ground system based on my own design.  And experiment with it.

BTW I believe the quarter wave "radial" situation you mention is close to the Franklin Antenna design that only one broadcast station KFBK in Sacramento has.  It is basically a vertical dipole (stacked balanced fed quarter waves).

Please correct me if I am wrong in any of the above areas.  I love to learn.

Kent
K9EZ

On Wed, Nov 12, 2008 at 12:48 PM, Guy Olinger <Guy.Olinger at sas.com<mailto:Guy.Olinger at sas.com>> wrote:

Kent, the problem with much of the ground radial flak (including the article referenced in the URL) is that it goes something like this:

Lawrence Livermore Labs is very smart and was paid by the government to do smart work.  They came up with Sommerfield Ground which got put in NEC2 and NEC4.

So we can run NEC2 and NEC4 and treat the model results as fact because of all the smart people.

The problem is that when you talk to the people responsible for the models THEY don't believe they have dirt solved at RF.  The intention of the Sommerfield ground was to get some measure of predictability of wire antennas IN THE AIR.  None of the principals involved thinks that the models are exact for wire ON or IN the ground.  And no one is paying them to find out.  A LOT of funding for a lot of things dried up with the end of the cold war.

What you do not see in a lot of internet expositions is raw data with case A, and A environment carefully qualified, and raw data with case B with its environment carefully qualified.  There is a simple reason for that...getting raw data for 160 meters is a genuine real first class pain in the *rse.  You have to account for ground moisture, the chemistry of the dirt, which is never constant, and take measurements.  Then do it all over again later to make sure your measurements are repeatable, and account for the almost inevitable variations, and maybe do the same thing 30, 50, 100 times over the seasons and identify any statistical variations.

It's far, far easier to do a NEC2 run in your nice warm house, and write a paper based on a graph showing overlaid curves from several model runs.

The seminal careful measurements in the 30's and 40's by Bell Laboratories and others, who had budgets, vast acreage, and a commercial mandate to do the work, do not agree with some of the model results for elevated systems. W8JI has done extensive comparative measurements on elevated vs. buried, and his measurements do not agree with some of the model results.  He's gone back to buried, and it's hard to argue with his results.

There remains, still, some number of poorly understood phenomena regarding the behavior of dirt at RF, which because they are poorly understood, mean the models poorly estimate.  To wit, if you construct a copper plane and base an antenna on top, there is a significantly less level of current detectable underneath.  Changing over to wires, at some concentration of wire radials, the wires begin to behave as if they were a sheet, the area underneath gradually starts to behave as if it's shielded. One thing for sure, it's not at four radials, and there is significant flux density underneath four radials. One measured variable is that it takes fewer radials to accomplish the same measure of shielding as one goes higher.  Four radials is fairly effective at heights over a quarter wavelength, talking 125+ feet in the air for 160 meters.  W8JI was measuring equivalence between 60 buried radials and 60 elevated radials at something like 8' (anti-garotting height) for 160.

Model results presented as facts based upon the popular reputation of a model is still a violation of basic science.  For commercial enterprise, the beef is location, location, location.  For science the beef is measure, measure, measure.

Where's the beef?

73, Guy.

From: pvrcnc-bounces at mailman.qth.net<mailto:pvrcnc-bounces at mailman.qth.net> [mailto:pvrcnc-bounces at mailman.qth.net<mailto:pvrcnc-bounces at mailman.qth.net>] On Behalf Of Kent Winrich
Sent: Wednesday, November 12, 2008 10:11 AM
To: Brian Alsop
Cc: PVRCNC
Subject: Re: [PVRCNC] Optimum # radials article

You can play with burying hundreds of feet of wire or you can go elevated:

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

As I mentioned in my presentation, it is most important to cover an area close in to the antenna.  There is not a big addition in coverage with the longer wires.  It is better (if you go buried) to have MORE then LONGER radials.  I suggested a 20' square of an interwoven 'grid" with about 1 - 2' squares to create a "screen" .  Elevate it if you can!

In this article a number of issues are skipped over (or I read to fast, which is quite possible).

Dont you find it interesting that they are suggesting a LOWER number of radials in poor soil?  That is because of ground loss.... something the elevated system is supposed to lower.

Another issues is that they talk about the NUMBER of radials versus the area covered.  So if I have 500' of wire, they are still suggesting that ALL radials be 1/4 wavelength.  Unfortunately they didnt try shorter, but more numerous radials.

BTW in our area, I always assume that we have poor (heh or NO) ground conductivity.

Here is a discussion and data about elevated versus standard ground system in Ham Radio Frequencies:

http://www.arising.com.au/people/Holland/Ralph/shortvert.htm

Here you will see that 3 -4 elevated wires can out perform 32 buried wires!

Kent Winrich

K9EZ/4

b0zo #143. www.ab0zo.com<http://www.ab0zo.com>

Somewheres near Fuquay

Ex Cheesehead

Packer Fan and Stock holder!

On Wed, Nov 12, 2008 at 8:35 AM, Brian Alsop <alsopb at nc.rr.com<mailto:alsopb at nc.rr.com>> wrote:

Guys,

This makes interesting reading.

http://www.ncjweb.com/k3lcmaxgainradials.pdf

It determines the optimum length and number of radials (40/80/160M) at given amounts of available wire.
The results are plotted and tabulated for various ground conductivity values.

Given the data one may conclude that on 160M 500' of radial wires (with optimum radial lengths) is within 1.5 db of 32000' of wire also with optimum radial length!   The cost to obtain the extra 1.5 db is astronomical.

It gives hope to those who previously thought they couldn't put up a LF vertical because of ground system costs.

73 de Brian/K3KO
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