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Author Topic: Ground Radials and Design Questions  (Read 5640 times)
KG4PES
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Posts: 21




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« on: July 21, 2011, 12:21:53 PM »

I am trying to work with the confines of a 1/3 acre lot with a house and other physical limitations.  My main question is this:  Is it a must to place the ground radials under the vertical antenna, or can they be more conveniently located and tied into the ground system. 

The reason for asking is this.  I can easily bury many ground radials on my property, but the location of where I need to hide a vertical antenna and/or load up a rain gutter is not conducive to easy and symmetrical ground radial installation. 

As everything in life and the design of my shack is a compromise, I wonder can I place the ground radials throughout my property and place a vertical or two any where I can hide them (which would not be directly above the radials)?

Thanks in Advance,
Adam
KG4PES
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K3GM
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Posts: 1776




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« Reply #1 on: July 21, 2011, 01:34:39 PM »

Think of radials on the ground as gatherers of the RF currents which are flowing back in from all directions towards the base of the antenna.   They're the fast track home as opposed to the actual soil.    Placing the radial system somewhere other than around the antenna and connecting the system to the antenna base with a single wire won't function as you would intend it to.  Just place as many wires as you can around the antenna.  If they have to be shorter in one quadrant than than the rest, it's ok.  Just make sure you connect the radial system to the shield of the coax by a low impedance path.  Something like copper foil is a good conductor.

Yon can share radial systems around multiple verticals by connecting their junction points, but this has to done in as many places as possible.
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N3WAK
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Posts: 274




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« Reply #2 on: July 21, 2011, 07:01:34 PM »

Adam--I agree with these other posters.  However, I found burying radials a lot of trouble.  I spent several days with a lawn edger making slits in the grass, going around my raised vegetable beds, my rows of blackberries, and lots of other obstructions in my yard.  Then I spent a lot of time pushing #14 insulated, stranded THNN wire from Lowe's into the slits.  Invariably, it was either too hot or too cold when I was doing this--the weather was never "just right," so I felt like Goldilocks while I was installing my radials.  After I put in about half of my crooked radials of various lengths, I decided to stop burying them.  I cut the grass relatively short, laid the radials down on top of the grass, and stapled them down every couple of feet with landscaping cloth staples from the garden section at Lowe's.  Now, you still spend a lot of time on your knees, but stapling the radials to the ground is a heck of a lot easier than burying them!  After a few months, the grass really does grow to cover the radials. 

I used a DX Engineering radial plate, which I think is a great product, and their Vertical Feedline Current Choke at the feedpoint.  I also use an RF choke in the shack.  Most of my radial wire came from Lowe's, although I used the DX Engineering stainless steel hardware to attach the wires to the radial plate. 

My QRZ webpage has a bit more info on my radial field. 

Good luck with your efforts!  The important thing is to put in a reasonable number of radials, arranged to fit in your yard, and use as short a run of good-quality coax as possible--I use "Bury-Flex" coax, which is great.  Your "real world" radial field may not look like the pretty diagrams of symmetrical radials in QST magazine, and you may be more than a few radials shy of the 360 used by some serious low band DXers, but I bet your vertical antenna will still work great. 

73, Tony N3WAK
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W8JX
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Posts: 5604




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« Reply #3 on: July 21, 2011, 09:17:50 PM »

I still question this need at least 30 and 60 is best. I guess my antenna should not work at all as it has none but then I guess it does not know any better. I heard VK3 calling CQ other morning on 20 and he was not too strong and no one was answering him so I gave him a call with 50 watts and we talked for 25 minutes and then signed as it was bed time down under. And guess what no LMR 400 (and run is 175 feet) and no 60 or even 30 radials. Do radials help, sure but do you really need 30 to 60, I think not.
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W6RMK
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Posts: 650




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« Reply #4 on: July 22, 2011, 10:20:48 AM »

The 30-60 recommendation is more about where you start to see no big improvement by adding more.

It's not that half a dozen doesn't work.. it's just that going from 5 radials to 10 will have a much bigger effect than going from 30 to 40, or even 30 to 60.

There's also a whole lot of tradition, stemming from the Brown, Lewis, Epstein work on broadcast antennas.  You install 120 radials of specified length, and the FCC lets you not have to make measurements in the field. If you're building a broadcast station, that gives you a choice between spending money on radials or spending money on field proof of performance tests.  (Broadcast stations must have a specified field strength at specified distances at one frequency, not too much, not too little, so you need a predictable, stable antenna system... this is VERY different than ham applications..)

The easiest way to connect all those radials together (if you're not doing the "twist the bundle and solder" approach) is to get ground bus bars that are usually mounted in a circuit breaker box.. They're $4-5, have a dozen or two nice holes with set screws, and actually intended for this kind of purpose.  No putting lugs on, no wrapping wire around a bolt..
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K5ML
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Posts: 25




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« Reply #5 on: July 22, 2011, 06:51:13 PM »

Hi Adam,

Some of the best empirical research on ground radials and their effect on vertical performance was done by Rudy Severns, N6LF. Here is one of his many excellent articles that will help answer your question:
http://rudys.typepad.com/files/qex-ground-systems-part-4.pdf

I have two ZeroFive ground mounted verticals: a 41' and a 33'. I live in the desert where ground conditions are allegedly poor. I experimented by adding 8 radials at a time and found that after 32 radials, I could not distinguish any improvement by going to 64. I know two hams who have excellent signals with no-radial verticals. One lives near Chicago and the other lives on the Mississippi Gulf Coast. Both have just a simple ground rod. The soil in both cases is obviously excellent.

If you need radials, a good rule of thumb is to make them as long as the length of the vertical. I have 40 radials on both of my verticals. The radials are of varying length and the patterns they are laid out in are far from perfect. My 33' vertical is next to a swimming pool and the radials wind around the yard in a pattern similar to a 3-sided swastika. Nevertheless, it works fine. Do the best you can with what you have and chances are you'll work a lot of DX and have a lot of fun. Good luck.

73,
Mickey, K5ML
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W0BTU
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Posts: 1626


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« Reply #6 on: July 22, 2011, 09:51:26 PM »

I still question this need at least 30 and 60 is best. ... t do you really need 30 to 60, I think not.

I agree. http://www.w0btu.com/Optimum_number_of_ground_radials_vs_radial_length.html
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K8IZ
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Posts: 17




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« Reply #7 on: July 31, 2011, 10:36:47 AM »

This is an interesting concept for a ground radial http://www.kiss-ssb.com
Called then and they claim its work great in boats and its about 14 feet long so to short for an actual 1/4 wave radial systen
I was thinking of using in my Toyota tacona as it has a composite pick-up bed and does not provide a lot of ground plane for HF operation.

Gary K8IZ
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W8JI
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Posts: 9304


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« Reply #8 on: August 02, 2011, 04:09:34 AM »

The optimum length of radials is NOT related to length of the vertical at all. That is an old wives tale that is false.

As a matter of fact, the SHORTER the vertical the longer radials need to be.

A half wave vertical can use a minimal ground system with just a few short radials.

A 1/4 wave vertical needs about 10-25 radials and they should be 1/8th wave or longer, and centered on the antenna base.

A 1/10th wave tall vertical needs even more radials for peak efficiency, perhaps 25-50, and they should be close to 1/4 wave long.

So you see, the truth is nearly the opposite of the old wives tale that radial length needs to be tied to vertical height!!!!

73 Tom
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KB2HSH
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Posts: 220


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« Reply #9 on: September 17, 2011, 06:38:07 PM »

W6RMK is 100% correct...going from 5 to 10 makes a HUUUUGE difference.  I just installed a Hustler 4BTV at my QTH (on the garage's flat roof to keep the XYL happy) and had 2 radials per band.  After 1 week, I have added 8 more.  The change is overwhelming.  My SWR on ALL bands is less than 1.9:1, and at 28.120, my SWR is flat, where before it was over 1.5:1.

Good Luck!

John KB2HSH
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