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Author Topic: Vertical Antenna Mounting Considerations  (Read 8852 times)
K9BAY
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« Reply #15 on: August 28, 2010, 06:49:41 AM »

I think I am going to go elevated for the upcoming winter months.  I can always move it to ground mount next spring.  Unless the elevated vertical doesn't perform, then I'll have some time to move it to a ground mount.

Thanks for the feedback.
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W9OY
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« Reply #16 on: August 28, 2010, 06:56:32 AM »

My experience mirrors W8JI's experience.  I think the real issue for a roof mount is height above ground (as a function of wavelength).  On 20M a roof mounted vertical is getting pretty ground independent as far as loss goes.  Where as on 80M a roof mounted vertical is still plagued buy considerable ground loss.  I also totally agree about the common mode issue in the roof mounted case. 

I'm not very convinced in the grand scheme of things that anything in the common suburban environment such as sheds and aluminum siding has much to do with anything when it comes to verticals.  If you live at ground level in some canyon of buildings in downtown Chicago or NYC that's a different story. 

If you ground mount a vertical what you want to do is MAXIMIZE your coupling into the dirt surrounding the vertical.  When you transmit, the vertical is inducing current in the surrounding ground and to maximize your signal you want to collect as much of that current as possible and send it back to your transmitter on the shield side of the circuit.  You do this with a lot of radial wire, that couples you into the mass of electrons below your antenna that are being excited by your radiator.  The whole purpose of an on the ground radial system is to couple you into this electron cloud and return the current to your transmitter.   

For a roof mounted vertical you want to MAXIMIZE the isolation from the ground and that is done by increasing the height (measured in wavelengths) above the ground.  There is nothing magic about "4 resonant radials" you would probably be better off with 30 radials above the ground as well since that number would tend to act as a low impedance shield from the ground and hence ground loss.  This is especially true if your roof mounted system is low in terms of wavelength (such as a 80M vertical on a 12 foot roof).   The larger number of radials would start to approximate a shielded plate and would solve the common mode problem etc. 

In either case a properly installed antenna with no corners cut on the radial system will probably get out about the same.  There is a reason these measurements have to be done with high accuracy, because if you don't use high accuracy the difference gets lost in the noise.
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W9OY
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« Reply #17 on: August 28, 2010, 07:10:19 AM »

PS I've trialed both systems (roof v ground) using the same radiator (butternut HF6V) which at least from 40-10 is a pretty efficient antenna.

73
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W4VR
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« Reply #18 on: August 28, 2010, 10:50:28 AM »

Elevate it.  You'll get better results.
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WA1RNE
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« Reply #19 on: August 28, 2010, 06:34:32 PM »

 I recommend reading both of these articles on elevated verticals.

 Both have echoed my results on 75/80 meters.

http://www.arising.com.au/people/Holland/Ralph/shortvert.htm

 Another good article on the subject can be found here, comparing 4-6 elevated radials to 120 on ground:

http://www.commtechrf.com/documents/nab1995.pdf


 If you have an IEEE Xplore account, check out this one by Christman:
  
  "AM broadcast antennas with elevated radial ground systems"

 Very interesting comparison of an AM broadcast band elevated vertical with 4 radials versus a conventional 120 radial ground mounted vertical.

 One difference should be noted: these antennas are being used by a corporation to make money, not win contests.

 Receiving can be a different matter. Vertical arrays or long horizontal antennas can be a big advantage versus a single vertical - on the ground or elevated.


 ...WA1RNE
« Last Edit: September 04, 2010, 09:05:43 AM by Chris Harris » Logged
K9BAY
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« Reply #20 on: August 29, 2010, 08:11:35 PM »

Thanks for the excellent articles.  I wish there was away to test your soil for potential ground loss.

So going "elevated" and using 4 radials on a 40-10M multiband antenna, what about radial length?  Should the length of the radial be for 40 meters?

Thanks again for the helpful information.

73, K9BAY
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WA1RNE
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« Reply #21 on: September 04, 2010, 09:05:04 AM »

 VK1BRH shows that it is possible to use shorter radials and obtain decent efficiency. The general consensus is to use 1/4 wavelength long radials on all bands for maximum decoupling, and if you don't have any physical restrictions there isn't a good technical reason not to.

 For 40, that's only 33.4 feet which is pretty manageable for just about everyone. If not, I would still simply bend them a little to accommodate property lines, etc.

 I used 0.2 wavelength radials with a 0.15 wavelength radiator to accommodate a special physical restriction I had to deal with. Later I tried 1/4 wavelength radials but didn't notice a significant difference while operating other than a slight change in feed point impedance. Admittedly I wasn't able to measure the effect but it served my purpose, especially in 10 degree F weather

 As for the soil, even the guys using verticals on the ground with 120 radials don't have a lot of control of soil conditions, especially in the far field, unless of course you pick an oceanview QTH.
« Last Edit: September 04, 2010, 09:07:48 AM by Chris Harris » Logged
K9BAY
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« Reply #22 on: September 04, 2010, 04:11:59 PM »

Thanks for the reply.

Do I need to have a radial 1/4 length for each band 40, 20, 17, 15 and 10?  Or just 33.4 feet length for all of the 4 radials?

Thanks!

K9BAY
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W5WSS
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« Reply #23 on: September 04, 2010, 05:10:03 PM »

Well here I go.....Everything I have read in this thread is good advice but,... one area to remember with respect to the elevated radial/s case is in the angle of slope downwards towards the ground. The benefits of this technique is often overlooked as advantageous and misunderstood even excluded as a viable consideration of part of the antenna. The slope angle of the tuned elevated radials usually around 45 degrees actually changes the definition of this antenna to center fed dipole and should not be considered a ground plane the distinction is because in a ground plane where the radials are at a right angle with respect to the vertical monopole horizontal oriented radials work to cancel the horizontal radiation and they do a good job when they are symmetrically oriented around the pole. IE 0,90,180 and 360 degrees respectively. Additionally The center fed dipole exhibits gain over and above an elevated 1/4 wave ground plane because the sloped radials not only help set the low loss feed point Rr but because they also add to the far Field gain that which a ground plane simply can not provide. So sloped elevated radials since they occupy as much vertical dimension as they do vertical dimension we now have a vertical dipole that is close to a natural 50-j0. 73
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W8JI
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« Reply #24 on: September 04, 2010, 05:14:22 PM »

Thanks for the reply.

Do I need to have a radial 1/4 length for each band 40, 20, 17, 15 and 10?  Or just 33.4 feet length for all of the 4 radials?

Thanks!

K9BAY

The problem with a question like this is you will get many answers of what people want to believe, not what they know as a fact. If you want a winning big signal, it takes work. If you just want to make contacts, it doesn't take much work. Anything much over a dummy load will work DX if you don't mind waiting your turn.


Hams have a particular misunderstanding of broadcast systems. We often think, quite wrongly, that a perfect ground is 120 buried radials and that 4 elevated radials equals 120 radials. Thus 4=120

Factually about 15-30 radials buried is the limit needed to have nearly 100% efficiency, not 120. The 120 comes from an FCC mandate for eliminating a full field proof, not what is really needed for "perfect". It is very misleading to claim 4 elevated equals 120 buried radials, because 4 elevated radials (at enough height) really equals 10-30 radials that are buried, depending on soil, band, and radial height.

Here's the other problem no one thinks about. When we elevate the radials, we have no real lightning  protection added. We also need to isolate the feedline for RF to get peak efficiency and to keep RF from following the feedline to the rig. We also, if it is multiband, need 4 radials for every band unless they are in a 3rd  harmonic relationship to some other band's radials.

If we just use 15-30 buried or surface radials (or more) we get all bands, some lighting protection, and minimal coax shield currents. For example my on the ground system of 35 radials ranging from 60 to 100 feet long (depending on directions) is out of sight, out of mind, offers lightning protection, and works as well as or better than 4 or 8 elevated radials would, and does it on any band from 160 to 10 meters. I can and do put any antenna there I want, and never have to worry. One ground fits all, and it never falls down.

The real factor that determines what you do is mostly physical. While height will often help on 10 through 20 meters because the antenna can get above ground clutter, it generally makes no difference at all and sometimes can actually hurt on 160 and 80.  Few people use an elevated system on lower bands, and for good reason.

If you want to see how much common mode you can have with four radials, look at this page:

http://www.w8ji.com/verticals_and_baluns.htm

You can have 20% or more of the antenna current on the coax shield with four radials!! Think how bad that can get with one or two radials per band!

Here's the bottom line....almost anything will radiate enough to make a lot of contacts. Anything that makes contacts will make some people happy as a lark. With my mobile antenna on my truck, I've worked Europe on 160 SSB and VK, JA, and other DX on 160 CW. That antenna is less than 1% efficient, and that is 160 meters! The most important thing is to have the antenna fit what you can do, and do as much work as you want to do.


73 Tom













« Last Edit: September 04, 2010, 05:16:40 PM by Tom Rauch » Logged
K9BAY
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« Reply #25 on: September 05, 2010, 07:30:33 AM »

Thanks for the info.  In Indiana, we are approaching fall, and winter after, so the threat of thuderstorms will be at a minimum.  My thinking was to set up the elevated vertical on a tripod, and then work on the ground radials next spring and then move the antenna to ground based.  I will be using a Balun Designs 4:1 Unun as recommended by the antenna manufacturer.

Here is the quote from the S9Antenna vertical antenna manual:

For elevated installations, use 4 radials, each ¼ wavelength at 7 MHz (33 feet,
5 inches long). Simply attach the 4 radials to the optional S9v Pipe Mount
Clamp below the base of the antenna and try to position the 4 radials
equidistantly around the S9v base. If possible, drop the radials away from the
S9v at a 45-degree angle to the base. Attach insulators to the ends of the
radials. Connect your coax shield to the clamp and radials. Do NOT run a wire
from the radials/clamp/coax shield to an earth ground.


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WA1RNE
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« Reply #26 on: September 05, 2010, 07:59:39 AM »

Quote
Thanks for the reply.

Do I need to have a radial 1/4 length for each band 40, 20, 17, 15 and 10?  Or just 33.4 feet length for all of the 4 radials?

Thanks!

K9BAY

 
 Yes, an elevated vertical requires tuned radials for each band. You mentioned 40 meters so I used that as an example.


 
Quote
Thanks for the info.  In Indiana, we are approaching fall, and winter after, so the threat of thuderstorms will be at a minimum.  My thinking was to set up the elevated vertical on a tripod, and then work on the ground radials next spring and then move the antenna to ground based.  I will be using a Balun Designs 4:1 Unun as recommended by the antenna manufacturer.

 My first impression was that you were using a trap vertical and didn't realize you were using one of the many 31/43 foot "all band" verticals. I'm not sure where S9 is coming from with 40 meter radials for all bands but that's not going to provide sufficient decoupling. If you use a tripod to support an elevated vertical, make sure it's insulated from ground as you don't want the feed point shield connected to earth. Also keep the feed line running to the shack along the ground or buried using acceptable methods.

 Because of the wide range of feed point impedances you will see on 20, 17 and 10 meters, I would also use install a tuner at the feed point, not at the shack.
 
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W8JI
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« Reply #27 on: September 06, 2010, 03:50:15 AM »

Thanks for the info.  In Indiana, we are approaching fall, and winter after, so the threat of thuderstorms will be at a minimum.  My thinking was to set up the elevated vertical on a tripod, and then work on the ground radials next spring and then move the antenna to ground based.  I will be using a Balun Designs 4:1 Unun as recommended by the antenna manufacturer.

Here is the quote from the S9Antenna vertical antenna manual:

For elevated installations, use 4 radials, each ¼ wavelength at 7 MHz (33 feet,
5 inches long). Simply attach the 4 radials to the optional S9v Pipe Mount
Clamp below the base of the antenna and try to position the 4 radials
equidistantly around the S9v base. If possible, drop the radials away from the
S9v at a 45-degree angle to the base. Attach insulators to the ends of the
radials. Connect your coax shield to the clamp and radials. Do NOT run a wire
from the radials/clamp/coax shield to an earth ground.





I think that is terrible advice. It tells me they don't understand the product they sell.

As WA1RNE says, that would only MARGINALLY decouple the feedline on 40 meters and 15 meters. Even on those bands you could expect significant coax shield current. On other bands where the antenna will really work, like 60 meters, 30 meters, and 17 and 12 meters that is a poor ground. The coax would be hot.

On 20 and 10 meters it is almost like no ground at all.

Why would you buy a vertical like that when you can buy a good trap vertical like a 4BTV or 5 BTV vertucal, or a Butternut trap vertical??? I really don't understand the fascination with these mismatched verticals, and very clearly the manufacturer often doesn't understand ground systems and safety.

If I were buying a vertical, I'd buy a good trap vertical have a BETTER signal on all bands from 40-10 without using a tuner. I'd also install a good ground system, and be done with it.

73 Tom
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K9BAY
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Posts: 144




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« Reply #28 on: September 06, 2010, 07:53:48 AM »

Tom, for one the COST!!!!!!!  I don't have $400 - $500 to lay down for a vertical.  The S9 Antenna is the best performance to cost antenna that I found during my extensive research.  Also 36 reviews, and a 5.0 rating, I think it will do a fine job.   

You can look at the reviews and comments.  Hopefully this will change your opionion.

http://www.eham.net/reviews/detail/8067

The bottom line is that I have to set it up and see what the performance is.  I will report back to this thread when I have done so.

73, Barry



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K2QPN
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« Reply #29 on: September 06, 2010, 07:56:18 AM »

I have used ground mounted Hustler verticals for years. I like them. I have worked 260 countries with the Hustler so they sure work. Currently I have a 5BTV with the 30 meter trap, the 17 meter add on and a 12 meter wire element. My experience shows the vertical is OK on 80M, good on 40M and 30M, OK on 20M, fair on 17M and 15M, and poor on 12M and 10M. I think the reason is that the antenna becomes electrically shorter as the frequency goes up.  A short vertical is shielded by trees and buildings. I also suspect the vertical is helped on 30 and 40 by being ground mounted. A second antenna might be the answer. Currently, I use the vertical for 80, 40 and 30 meters and a Broadband Hexx Beam for 20 to 6 meters.

73, Bob K2QPN
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