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Author Topic: 43' Vertical Radials - More shorter vs. Less longer  (Read 5036 times)
WT3O
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« on: September 19, 2012, 11:45:21 AM »

I've decided to upgrade my antenna system from a G5RV to a 43' vertical. I ordered the antenna in June and installed it in August (an MFJ-2990). I have a ground rod at the base for lightning protection. I currently have only 8, 15' radials.

I've been doing some research and some say that more, but shorter, radials are better than fewer, but longer, radials. I don't have a problem laying more radials, but I just want the best performance possible from this antenna, so before I go laying more radials, I thought I'd see what anyone thinks about more shorter radials vs less longer radials.

I just don't understand how shorter radials would be more beneficial because at 75M, 15' is only 1/16 wavelength.
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W5DXP
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« Reply #1 on: September 19, 2012, 12:01:58 PM »

I just don't understand how shorter radials would be more beneficial because at 75M, 15' is only 1/16 wavelength.

If the radials are buried, the ground detunes them so a reasonable rule of thumb for buried radials is 1/8WL on the lowest frequency of operation. Personally, for 80m operation, I wouldn't bury anything shorter than 30 feet.
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KF6ABU
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« Reply #2 on: September 19, 2012, 12:12:07 PM »

http://rudys.typepad.com/files/qex-ground-systems-part-4.pdf
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AD4U
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« Reply #3 on: September 19, 2012, 02:25:13 PM »

Assuming your G5RV is at a decent heighth (50 feet or more) let us know if the 43 foot vertical actually out-performed it, especially on receive.

Dick  AD4U
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KC4MOP
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« Reply #4 on: September 19, 2012, 03:18:48 PM »

Once the radials are on the ground there is no 'tuning' of the radials. When radials are elevated about 15 feet off the ground; then you start 'tuning' and you only need 6 or 8 radials per band.
They are to complete the A.C /RF circuit.  The idea of concentration of radials close to the base is to reduce the effects of losses in the Earth. Typical broadcast stations (AM) use 120 radials 120 feet long. For us poor Hams 60, as long as you can lay out there, is sufficient.
Chicken wire is a good one to lay near the base of the tower. Lay down as much as you can afford.
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N8CMQ
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« Reply #5 on: September 19, 2012, 04:49:25 PM »

I have 125 radials filling a 60 foot square.
I used 22 ga copper plated steel welding wire, but I would recommend stainless or copper instead.
My 4 band trap vertical has edge to edge SWR under 2:1 on 10m 15m and 20m. On 40m, the SWR is below 2.5:1.
I also have an 80m resonator, but the bandwidth is narrow due to it being a resonator and not a trapped section.
My next experimental antenna will be a cone, or inverted discone...
I know there is a lot of theory saying many short radials, but I go as long as I can fit in the area.
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N3OX
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« Reply #6 on: September 19, 2012, 04:58:31 PM »

I just don't understand how shorter radials would be more beneficial because at 75M, 15' is only 1/16 wavelength.

They're not.  You're probably getting to the limit where that idea stops making sense.  At some point you just have to pony up for more wire Smiley

If you have the SPACE for quite long radials, say 0.3  or 0.5 wavelength, but can't afford much wire, then maybe chopping 0.3wl radials into three times as many 0.1wl radials would be really beneficial.  If you're already at 1/16 wavelength I wouldn't go shorter but I would add more, and also add longer ones if you can fill out a square or rectangle or other shape... not many people have round spaces to work with Smiley

You have to be careful about rules of thumb like "more and shorter is better than few and longer."  It's good advice for people who might not feel like putting down a lot of wires or who think that radials on the ground need to be a free-space quarter-wavelength long... four 1/4 wave radials on the ground is a bad radial system, and N6LF showed that at his location, it's SO bad that a ground rod significantly improves it.  Eight eighth wave or maybe even sixteen sixteenth wave could be better.

But it's not a rule that makes mathematical sense forever.  A thousand 1/1000 wavelength radials is an awful system too.
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W5WSS
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Posts: 1772




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« Reply #7 on: September 19, 2012, 05:50:25 PM »

Hello, W8ji is progressing with a multi band counterpoise technical helping to demystify some of the stereotypical rhetoric and help with relaying sound radial counterpoise construction techniques.
Check his website.
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KK5J
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« Reply #8 on: September 19, 2012, 08:07:48 PM »

I agree completely with N3OX. I don't consider it as an either/or situation. I go as long as I can and have put down as many as I can. Laying down more wire is probably the best advice anyone can give. Good luck with your project.
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K0OD
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« Reply #9 on: September 19, 2012, 09:16:49 PM »

Quote
"I've decided to upgrade my antenna system from a G5RV to a 43' vertical. "

As the owner of a 43' vertical for several years, I'm troubled by that first sentence. I'd take a high G5RV over my vertical for many purposes. And I have a very good radial system under my vertical.

How high is your G5RV? What bands do you operate and do you mostly work DX or ragchew?

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RFRY
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« Reply #10 on: September 20, 2012, 02:25:09 AM »

Below is a link to a NEC4 study showing how earth conductivity at the antenna site affects the radiation efficiency of a 10-m vertical using 32 x 10-m buried radials, on 1.85 MHz.

The r-f ground connection loss vs earth conductivity for that set of radials on that frequency would be essentially the same if used with a 43' vertical, so that data may be useful here.

http://i62.photobucket.com/albums/h85/rfry-100/10m_Vert32Buried_Radials.jpg
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K2DC
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« Reply #11 on: September 20, 2012, 03:35:22 AM »

I agree with W5DXP, more is always better than longer.  A friend of mine Brian, N2MF published an extensive modeling study in QST many years ago.  The study showed that more is always better, and that the benefits only improve substantially up to about 1/8 wavelength at the lowest frequency.  There is some improvement from there up to 1/4 wavelength but longer than that is hardly worth the copper.

73 All,

Don, K2DC
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WT3O
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« Reply #12 on: September 20, 2012, 06:24:59 AM »

Thank you all for your wonderful responses!

I have the space to lay down some longer radials (my house sits on an acre lot with no HOA).

Now here is my next question: are a lot of longer (60'+) radials better than radials cut for a specific band (9' for 10M, 12' for 15M, etc...)? I operate from 10M down to 80M.

My G5RV is only about 10' up in the air (I know it should be higher), so I'm expecting the vertical, with better feedline (LMR-400 as opposed to RG-8X on the G5RV) and proper radials, to outperform the G5RV.


73 de WT3O
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RFRY
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« Reply #13 on: September 20, 2012, 07:09:24 AM »

> Now here is my next question: are a lot of longer (60'+) radials better
> than radials cut for a specific band (9' for 10M, 12' for 15M, etc...)?
> I operate from 10M down to 80M.

The function of buried radials is to provide a low-loss path for the conducted r-f currents flowing in the earth within about 1/2-wavelength of the monopole to return to the r-f ground terminal of the antenna system.  Producing that low loss doesn't require buried radials to be resonant.

The goal is to make the set of buried ground radials very dense in that circular area.  Broadcast stations often use 120 x 1/4-wave radials.  If the set of buried radials is dense out to least 1/4-wavelength radius on 80 meters it will still be dense on the higher bands.

If earth conductivity at the antenna site is very good (~10 mS/m and above), then fewer and shorter radials might be acceptable, as shown in the NEC4 study I posted.
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W8JX
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« Reply #14 on: September 20, 2012, 07:34:37 AM »


My G5RV is only about 10' up in the air (I know it should be higher), so I'm expecting the vertical, with better feedline (LMR-400 as opposed to RG-8X on the G5RV) and proper radials, to outperform the G5RV.


Do not bet the farm on it. The 43 foot vertical will be at a disadvantage on 20m and above with a higher angle of radiation. 
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