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Author Topic: Radials on vertical antenna  (Read 3342 times)
M5AEO
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Posts: 259




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« on: November 19, 2011, 02:25:23 AM »

What would happen if the radials on my vertical antenna were longer than the driven element?!
Just a thought because this is possible in my situation.

M5AEO

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G3TXQ
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Posts: 1464




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« Reply #1 on: November 19, 2011, 04:12:27 AM »

What would happen if the radials on my vertical antenna were longer than the driven element?!
Just a thought because this is possible in my situation.M5AEO
What frequencies?

Ground radials or elevated radials?

Steve G3TXQ
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AD4U
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Posts: 2153




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« Reply #2 on: November 19, 2011, 05:27:45 AM »

Assuming HF operation.................

Ground mounted vertical - radials of excessive length not that important, but longer is not necessarily better (in this case - HI)

Elevated vertical - "correct" radial length is important

Dick  AD4U
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WB6BYU
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« Reply #3 on: November 19, 2011, 07:36:36 AM »

I regularly build my 2m ground plane antennas this way - 18" for the radiator, 24" for the radials.

There are conditions where it will work (and may be the best approach), and others where it
won't / isn't.  More detail in your exact circumstances would help use to give better advice.
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K0ZN
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« Reply #4 on: November 19, 2011, 03:51:19 PM »

Hi.

Assuming you are talking about a ground mounted vertical on HF:  ALL the radials do is reduce the ground losses by being better conductors than dirt. ( Duh!)
Length of in-ground radials is not critical, but they should generally be at least 0.2 wavelength if possible. Longer, up to about a half wave length, is "better",
but it becomes very marginal as to benefits once you go over 1/4 wave length. What is more important is the number of radials. You are far better off with a
lot of shorter radials than a few long ones because the RF current is highest near the base of the antenna and more radials reduces the ground losses near
the base where the current is highest.

In the real world, an 'excellent' ground radial system would probably consist of 60 to 75 radials that are 1/4 wave length long. If you are a screaming perfectionist, put in 100. Going back to the number of radials, you would be better off with 40 radials that are 0.15 wave length than 20 radials that are 0.25 wavelength. Again, this assumes in or on ground radials. FYI:  there is no point in bending radials around corners, etc. The RF currents flow in straight lines from the base of the antenna and zigging and zagging radial wires to make them longer has very little benefit.

If your yard will not allow a symetrical radial system that is OK. Just do the best you can. Lastly, another common question is what wire size should be used? The answer is about anything. The main consideration is simply mechanical strength. U.S. wire gauges #16 and #14 seem to be very good but smaller is fine if it won't get broken.
Do NOT use steel wire! (It will quickly rust and become ineffective.) Use copper wire. Aluminum can be used but some soils will corrode it rather quickly and you also have to deal with possible corrosion at connection points. Bottomline: copper is the best wire....and yes, you can use insulated wire if that is what you have.

If you are talking about a VHF antenna or Elevated radial wires for HF, not in contact with the ground, they DO operate as "tuned" and must be 1/4 wavelength.

73,  K0ZN
« Last Edit: November 19, 2011, 03:54:34 PM by K0ZN » Logged
K2YO
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Posts: 436




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« Reply #5 on: November 20, 2011, 12:05:08 AM »

One the subect of how many radials, N6LF has done some very interesting research on how many ground radials you need. Some of it can be found here;
http://www.antennasbyn6lf.com/files/antenna_ground_system_experiment_1.pdf

If you belong to the ARRL, look for a series of articles we published in QEX in 2009 on similar subjects.

He puts some hard data to what has been a subject of much speculation over the years.

Bernie
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W8JI
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Posts: 9304


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« Reply #6 on: November 20, 2011, 06:32:01 AM »

One the subect of how many radials, N6LF has done some very interesting research on how many ground radials you need. Some of it can be found here;
http://www.antennasbyn6lf.com/files/antenna_ground_system_experiment_1.pdf

If you belong to the ARRL, look for a series of articles we published in QEX in 2009 on similar subjects.

He puts some hard data to what has been a subject of much speculation over the years.

Bernie


He also warns his results only apply to his situation, and should not be assumed to apply in other cases.

:-)

It will always be this way, because the earth is not homogeneous.
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K2YO
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Posts: 436




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« Reply #7 on: November 20, 2011, 06:33:49 AM »

Well that will always be the way when lawyers are around, hahahhaha.
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NZ4Z
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Posts: 173


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« Reply #8 on: November 22, 2011, 06:48:15 AM »

Here's a different thought......I recently bought a Zero Five 43 ft vertical 10-160 ..... and at the suggestion of a friend, who has tried it with many radials also, I only used 2 8ft ground rods. This this works awesome....people can't believe I'm on a vertical. I have talked all over the world, and most of the time bust through the pile ups.....never more than 2 or 3 calls.
So....you may want to try the simple approach 1st.

73

Steve
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M5AEO
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Posts: 259




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« Reply #9 on: November 25, 2011, 03:13:29 PM »

Thank you everyone for the useful and interesting replies.  Just to answer a few questions:  the antenna is for HF, it is a helical vertical (one quarter wavelength at 7mHz).  It is mounted on my appartment balcony about 60 feet above ground level. At the moment I have 14 radial wires connected to it: they vary in length but are cut to quarter wave for each band, up to a maximum of 33 feet for 7mHz, which is the lowest band I can operate it on.  I am using thin insulated copper wire for the radials, which are spread out on the decking of the balcony, or the longer ones drape over the sides and drop down vertically.
The antenna works amazingly well, and I recently worked my first ever VK with it.
I was just curious about the radial lengths as I could, in practice, have 60 foot long wires attached; but from your replies it would appear that it's not worth the trouble!
Again, many thanks and 73
Jonathan, M5AEO


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W8JI
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Posts: 9304


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« Reply #10 on: November 25, 2011, 05:10:11 PM »

The golden rule of awesome super performance:

Any antenna that makes a contact we have not made before is awesome and/or works great, super, wonderful, etc., and can hardly be better.

This is true no matter how it really works.


:-)

73 Tom
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WB6BYU
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Posts: 13033




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« Reply #11 on: November 25, 2011, 05:40:58 PM »

With elevated radials as you describe, they need to be resonant for the bands you are
operating.  And while a 3/4 wave radial will be resonant, if it is handing down the current
in the bottom 1/2 wave will be out of phase with that in the vertical + the top 1/4 wave
of the radial, giving you a null at low angles.  That's probably not what you want.  Keep
them 1/4 wave long.

The next question is how well your 40m helical whip works on the higher bands - there
is no guarantee that it does.  I've seen some types that were designed to do so, and
others that were quite lossy due to internal resonances in the antenna even when they
were matched to a low SWR with a tuner.
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AD6KA
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Posts: 2232




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« Reply #12 on: November 25, 2011, 05:43:07 PM »

Quote
It is mounted on my appartment balcony about 60 feet above ground level. At the moment I have 14 radial wires connected to it: they vary in length but are cut to quarter wave for each band, up to a maximum of 33 feet for 7mHz, which is the lowest band I can operate it on.  I am using thin insulated copper wire for the radials, which are spread out on the decking of the balcony, or the longer ones drape over the sides and drop down vertically.

1/4 wave cut radials laying on the decking?
You only need to cut radials to 1/4 wave when
the antenna feedpoint is completely suspended in the air. They are
coupling to the decking and acting as any old ground radials.
Which is better than nothing, but not worth the effort
to cut them to 1/4 wave.

You must have HUGE apartment deck if I am reading this right.
« Last Edit: November 25, 2011, 08:37:28 PM by AD6KA » Logged
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