[PVRCNC] Optimum # radials article

Wed Nov 12 12:48:30 EST 2008

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] 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
_______________________________________________
PVRCNC mailing list
PVRCNC at mailman.qth.net<mailto:PVRCNC at mailman.qth.net>
http://mailman.qth.net/mailman/listinfo/pvrcnc

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.qth.net/pipermail/pvrcnc/attachments/20081112/28e69d02/attachment-0001.htm