Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Radials and Ground Conductivity in So Cal  (Read 1504 times)
WD6S
Member

Posts: 19




Ignore
« on: September 27, 2007, 12:17:20 PM »

First, I am a new extra and don't have a hundred years experience or knowledge. But I'm learning, which is fun.

My first HF antenna was a Hustler vertical, which did not perform very well for me. I tried adding radials which did not have any noticeable effect.

I want to move the vertical to our desert cabin in eastern San Diego County but I wonder about the viability of radials there.

Obviously the desert is quite dry (so is San Diego for that matter). I assume mineral ions in solution in the ground moisture support ground conductivity.

How dependent are radials on ground conductivity?  

If ground conductivity is important, is there a technique to measure it?

If ground conductivity is important, is there a way to improve it?

Your suggestions are appreciated. Thanks in advance

Bob
WD6S
Logged
K5LXP
Member

Posts: 4479


WWW

Ignore
« Reply #1 on: September 27, 2007, 12:30:26 PM »

> How dependent are radials on ground conductivity?

Comparatively, very little.  Consider the resistance of a piece of copper wire versus a bucket of dirt.  That conductivity you *can* control with an adequate counterpoise on top of the dirt.  There is a secondary effect of what happens in the far field of an antenna, and that's where ground conductivity that you *can't* control will make a difference.  The upshot of that is even on saltwater radials are still important, but the antenna will work better because the surrounding area beyond the near field has better conductivity, versus out in the middle of a sandy desert.  What you do in the near field (that you can control) will have a significant impact on efficiency and pattern, so I wouldn't worry much about soil conductivity in the far field (that you can't change anyway).


> If ground conductivity is important, is there a
> technique to measure it?

Yes.  There is a procedure in the "Low Band DX'ing" book by ON4UN.  It might be interesting to use for modeling, but there's not much you're going to do to change it.


> If ground conductivity is important, is there a way
> to improve it?

Yes. Flood several dozen square acres of land with saturated saline solution or cover it with aluminum foil.


Mark K5LXP
Albuquerque, NM
Logged
N0BLM
Member

Posts: 10




Ignore
« Reply #2 on: September 27, 2007, 12:54:13 PM »

Bob,

here is a link that helped me

http://www.geocities.com/SiliconValley/2775/gndsys.html?200718

I live about 3 hours north of you at China Lake Cal

I water my system to keep swr's down to 1.1 or better, due to large amounts of caliche in the ground

also I stay within less than a 1/4 wave lenght of my system, which in some cases may be hard to do

Good Luck
N0BLM  Mark








Logged
WA3SKN
Member

Posts: 5475




Ignore
« Reply #3 on: September 27, 2007, 12:57:57 PM »

The radials REPLACE the ground conductivity, as such.
And the current flow is directly below the antenna, so the lowest resistance is wanted there.
Thats why the more metal under the antenna, the better!

-Mike.
Logged
KB1LKR
Member

Posts: 1898




Ignore
« Reply #4 on: September 27, 2007, 01:04:30 PM »

See: http://www.fcc.gov/mb/audio/m3/index.html
for a map of Effective Ground Conductivity in the USA -- used for estimating propigation of AM broadcast stations
(from: 47 CFR 190 http://a257.g.akamaitech.net/7/257/2422/13nov20061500/edocket.access.gpo.gov/cfr_2006/octqtr/pdf/47cfr73.190.pdf ).

I expect local measurements would be done using a megohmmeter and driven conductors -- in fact here's a method from the 1994 ARRL Antenna Handbook:
http://www.amfone.net/ECSound/K1JJ12.htm

You may also find useful information in one of William (Bill) Orr, (W6SAI)'s books, I'd start with: "HF Antenna Handbook" or "All About Vertical Antennas" (w/ Stuart Cowan, W2LX).
Logged
WA3SKN
Member

Posts: 5475




Ignore
« Reply #5 on: September 27, 2007, 01:10:03 PM »

Try making a counterpoise out of welded wire fencing, or sheet metal.  Copper flashing is too expensive for this project.

-Mike.
Logged
AC5E
Member

Posts: 3585




Ignore
« Reply #6 on: September 27, 2007, 01:16:11 PM »

Several friends of mine in the high desert use MIG welding wire for radials. The stuff is fairly cheap and stands up to the conditions quite well. In theory there should be some difference in field strength between copper and MIG wire, but my FS meter can't find it.

The only gotcha is the need to make a good mechanical connection at the base of the vertical. A couple of wraps between two stainless steel washers and tighten 'er down gets the job done.

73 Pete Allen  AC5E
Logged
N6AJR
Member

Posts: 9906




Ignore
« Reply #7 on: September 27, 2007, 01:16:45 PM »

look at radials as 1/2 of a big capicitor with the ground as the other half. the more radials you have the better the coupling to the earth.

it ain't exactly correct, but it makes it easy to think about
Logged
WA2ONH
Member

Posts: 253




Ignore
« Reply #8 on: September 27, 2007, 03:58:37 PM »

"If ground conductivity is important, is there a technique to measure it?"

Yes. Check out "Antennas By N6LF" at
http://www.antennasbyn6lf.com/

TOPIC: "Soil parameter measurements at HF"
http://www.antennasbyn6lf.com/2005/05/soil_parameter_.html
----------------------------------------------------------
One of the basic inputs to antenna modeling programs are the ground conductivity and relative dielectric constant.  Frequently however, modelers have no real idea what their particular ground characteristics are.  It is possible to make useful soil parameter measurements at HF which are sufficiently accurate for modeling purposes.  The nice thing is that these measurements are not very difficult requiring only a very simple mechanical assembly, say a rod and a piece of screen, and an impedance bridge like an MFJ259 or similar units. The following file has a detailed discussion of this kind of measurement: ground parameter measurements, 1 MB. I recently gave a talk at the Dayton Hamvention. Here are the slides: Dayton 2005 slides, 220 kB.

Sometimes it is handy to know the skin depth and wavelength in a particular soil. Skin depth and wavelength in soil, 70 kB.
-------------------------------------------------

Good Luck!
73 de WA2ONH Charlie
Logged

73 de WA2ONH dit dit    ...Charlie
----------------------------------------------------------------------------
"No time is ever wasted that is spent LEARNING something!"
WD6S
Member

Posts: 19




Ignore
« Reply #9 on: September 27, 2007, 04:20:54 PM »

Thanks for all of your rapid and voluminous responses. It will take a while to digest it all, and try them out. Your responses were to the point, and not flippant or rude, which as a newcomer I very much appreciate. Some folks find sport in roasting rookies like me.

Bob
WD6S
Logged
WA1RNE
Member

Posts: 825




Ignore
« Reply #10 on: September 27, 2007, 05:43:18 PM »


 I'd work on your first question and not be so concerned about soil conductivity - which as others have said you really can't do much about without jumping through hoops.


 Was the vertical ground mounted or elevated? If elevated, how many feet off the ground?

 How many radials did you use?

 Which band(s) were the radials cut for?

 Any issues tuning the antenna?

 
 WA1RNE
Logged
KE3WD
Member

Posts: 5689




Ignore
« Reply #11 on: September 27, 2007, 06:51:11 PM »

No, Radial wires underneat the vertical do not have to be copper.  

As already mentioned, MIG wire can work, so can Aluminum, even steel electric fence wire can work for radials.  

What is most imporant is MANY radials do the better job and that is where a lot of hams miss the boat.  

By many, I mean anywhere from 30 to 60 radials or more...  

And longer is, of course, better.  No need to measure really, just lay 'em out there.  

And the previous poster asks the right questions about the rest of it IMO.  


KE3WD
Logged
K9KJM
Member

Posts: 2415




Ignore
« Reply #12 on: September 27, 2007, 11:24:24 PM »

The steel fence or copper plated welding wire will NOT last long in normal type soils! But will change to iron oxide (rust) within a year or so.

The super dry desert conditions MIGHT have a different effect, Such wire MIGHT last longer under those conditions.

Around here, Bare copper wire is the choice for radials. (Buried in the ground anyhow)  Elevated radials are another story.

Commercial AM broadcast stations generally try to find the lowest, Wettest "swamp" land possible for transmitter sites, Then run out 120 10 gauge copper radial wires from the base of the tower.
Logged
WA3SKN
Member

Posts: 5475




Ignore
« Reply #13 on: September 28, 2007, 05:30:02 AM »

It's hard to find a "Wet Swamp" in the desert!
It's also hard to bury wire in solid rock!

-Mike.
Logged
AD4U
Member

Posts: 2164




Ignore
« Reply #14 on: September 28, 2007, 06:35:12 AM »

Another source for radial wire is electric fence wire.  It comes in 1/4 mile spools and is very stable out in the weather.  Last time I bought some a 1/4 mile spool cost around $15.
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!