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Author Topic: Ground mounted Vs Elevated vertical  (Read 8385 times)
KC2PHJ
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« on: March 04, 2010, 08:04:19 AM »

What are the advantages or disadvantages for ground mounted vs elevated verticals for 6 - 20M?

Dave
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N0CGF
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« Reply #1 on: March 04, 2010, 08:31:38 AM »

I elevated my Hustler 4btv & 6btv antennas from ground mounted. I live in a in the city with a small lot and houses around the Vertical Antenna. Because I was up above the on ground objects I was able to get out on the upper bands MUCH Better. Just my experience at my 2 locations.  73's N0CGF Dennis
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N0CGF
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« Reply #2 on: March 04, 2010, 08:36:00 AM »

I forgot to state that the Elevated Radials were more difficult to install and tune.  That was the only down side I encountered with the Elevated Vertical installation.  73's N0CGF
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WB5JEO
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« Reply #3 on: March 04, 2010, 08:46:32 AM »

If it's your only antenna, the most credible technical discussions I've seen lead me to believe that there's some validity in claiming an elevated mount with tuned, elevated radials offer some more versatile elevation patterns. But if you're primarily interested in DX, a ground mount, assuming an adequate ground screen, puts most of the radiation at a low angle, which is where you want it. You can back it up with horizontal wire for higher angles favoring more local work. But like so many things about antennas, the performance differences are often not so great in terms of actual working experience. There will always be some distances at which one or the other is observably better, but that's true with all antennas.

Obviously, different physical layouts may make it easier to install one or the other. Elevated verticals with elevate radials requires some points to tie off the radial ends or the non-conductive end supports, often having the radials and end ropes double as guying for the support mast. (XYL alert.) And a ground mount means installing relatively more wires, with the advantages (maybe) that they can be out of sight sewn just under the sod and of no critical length. A round mount relieves you of worrying about radial tuning or detuning by proximity to metal objects. Both installations can be done in a narrow space, with some modest alteration to the horizontal pattern on account of the way radials may have to be distributed. Usually the choice is dictated by one or the other of ground or elevated antenna mounting being most acceptable in a particular place. (The elevation pattern of an elevated ground plane antenna is somewhat unpredictable, because we rarely have solid information on local ground conductivity. We have the same unpredictability for horizontal antennas, for the same reason.)

On six and perhaps on ten, there may be considerations favoring elevated mounting if there's some interest in a repeater or a friend's location that's at some distance, since elevation give you some more line-of-sight range (really a bit more than literal line of sight). For DX on HF, adequately installed ground and elevated 1L/4 and 5L/8 verticals will both have similarly low take-off angles, with the elevated ground plane verticals having one or more higher angle lobes. Vertical dipoles are, of course, free from radial issues but not from height above ground issues.
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WA2ONH
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« Reply #4 on: March 04, 2010, 08:51:05 AM »

A good read and starting point for elevating any vertical antenna system is at:

Antennas by N6LF Rudy Stevens
http://www.antennasbyn6lf.com/

SEE: 7-Part QEX published articles now posted on his web site.

Field tests on a HF Vertical with both ground and elevated radials of various lengths to determine the best performance level.

http://www.antennasbyn6lf.com/2009/12/series-of-qex-articles-on-ground-system-experiments.html

Also, look at ?QEX Letter to the editor" article at:
http://www.antennasbyn6lf.com/2010/02/qex-letter-to-the-editor.html

This supplemental letter details additional details on the math and assumptions developed for the field tests.

73 de WA2ONH Charlie
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73 de WA2ONH dit dit    ...Charlie
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"No time is ever wasted that is spent LEARNING something!"
N3OX
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« Reply #5 on: March 04, 2010, 08:52:08 AM »

The big advantage of ground mounting is that you can use random length nonresonant radials and don't have to cut them to specific lengths.  You need a lot of radials but they're basically invisible and don't bother anyone once you put them down.  I just picked a location for my vertical and ran radials out to the edges of my yard.  No big deal.  For an elevated vertical, you need at least a couple resonant radials for each band, and it's good to use a choke on the coax feedline too.  This is a little time consuming.

However, elevating a vertical will allow the radiated fields to clear surrounding objects a lot better and does change the radiation pattern a little.  Whether or not that matters much depends on your surroundings, keeping in mind that on the higher bands, smaller and smaller objects, terrain features, etc are more important, smaller conducting objects are more likely to interfere, etc.  Having a car next to a 6m ground mounted vertical is like installing an 80m vertical near a big metal warehouse.

You'll make contacts on a ground-mounted 6m vertical but only because you can make contacts on a 6m anything :-)

All in all, I would go with an elevated system for a 20 thru 6m vertical even though you'll need resonant radials for each band.  On 40m or 80m, local clutter is unlikely to matter as much and significant elevation is expensive and difficult.  On the high HF bands and 6m, it might really help to elevate the antenna.

For the low bands I prefer a ground mounted vertical because otherwise you have to have a giant canopy of wires and it's just hard to elevate.  If you have a lot of space where no one needs to go on the low bands, sometimes elevated radials can save work in achieving a certain amount of ground system loss, but it's easy to make a good, low loss radial system on 20 through 6m with a reasonable amount of wire and a reasonable amount of space...

It's just that even with negligible loss around the base of the vertical, you still end up with a lot of stuff in the way for the radiation from an upper HF/6m ground mounted vertical.  The amount of the effect depends on a lot of factors, but getting the antenna up in the clear is pretty much certain to be a little better than burying it in wavelength-tall or half-wavelength tall objects.

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WA2ONH
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« Reply #6 on: March 04, 2010, 09:26:00 AM »

The QST March 2010 N6LF Rudy Severns article (4-pages) is a shortened version of the QEX 7-part series. The 7-Part article (30-pages)is referrenced in the "NOTES" section.

73 de WA2ONH Charlie
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VA3GML
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« Reply #7 on: March 05, 2010, 07:18:15 AM »

For what it's worth.

30 years ago, I had a Hy-Gain 18AVT vertical as my antenna. It was mounted on top of an apartment building with about 6 radials laid across the roof and cinder blocks to keep them in place. It worked ok but not outstanding. I went 'off the air' for about 10 years and when I got back on, I bought a Hy-Gain 14AVQ vertical, purely because I had a Hy-Gain antenna before. This time, it was mounted on a roof of a 2 story house with a counterpoise system. Again, it performed ok. I went off-the-air again (raised the family) and have recently come back on. This time though, I took the time to really investigate all the different vertical antennas out there. When the dust settled, I chose the Butternut HF6V. It appears that 'traps' are 'lossy' and after checking reviews on a variety of assorted sites (including eham), the Butternut sounded like the best option...especially because there are no traps. I have it ground mounted with only 13 radials, mounted in a semi-circle (like a half moon) just under the surface and even though the bands haven't been great, generally, if I can hear them, I can work them. Lately, we have had some pretty violent storms (wind & lightning) and I watched as the antenna was pushed down to around 30 degrees...and it popped back up each and every time the wind died down. Im my opinion, ground mounted seems superior in both performance (low take-off angle for DX) and handling nature.
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N5YPJ
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« Reply #8 on: March 05, 2010, 08:04:11 AM »

On 6 - 20 in my opinion the best way to go is elevated to get the antenna above surrounding objects that could interfere with the antenna's operation and to not have to lay as many radials on the ground. Four elevated radials are said to equal 60 + on the ground and at 20 meters a 1/4 wave radial is only roughly 17 ft long. My vertical is elevated w/ 4 radials per band and if I were to do it again it would be elevated.
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W4VR
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« Reply #9 on: March 05, 2010, 08:13:58 AM »

An elevated vertical with radials is manageable on 20 through 6 meters...but becomes cumbersome at lower frequencies as you can well imagine.  I use a ground-mounted vertical with 50 long radials on 6 meters..I've compared it to a 6 meter dipole at 15 feet and I get better results with the vertical.  The reason I did the vertical was for convenience...I already had a 160 meter inverted-L using the same ground screen.
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N3OX
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« Reply #10 on: March 05, 2010, 11:28:40 AM »

I chose the Butternut HF6V. It appears that 'traps' are 'lossy' and after checking reviews on a variety of assorted sites (including eham), the Butternut sounded like the best option...especially because there are no traps.

Generally, all multiband antennas will be lossier than, for example, a simple quarter wave vertical.  But it's certainly not as simple as the marketing quote on Butternut's website: 

"The matching network used is an ingenious combination of high-Q coils fabricated from large diameter aluminum wire, and heavy duty high voltage ceramic transmitting capacitors. Needless to say, there are no traps, "high performance" or otherwise. Traps cause loss. Period. "

Stubbing causes loss.  Coils cause loss.  Heavy duty high voltage ceramic transmitting capacitors cause loss.  Every possible circuit that is not made of superconductors has some heat losses associated with it. 

And generaly, making an antenna resonant on many bands relies on an increase in increased energy storage in the antenna system... the resulting circulating currents from the extra energy storage in coils, stubs, capacitors, traps, whatever drive the loss up a bit.

But here's the thing.

But what matters is not the fact that there is loss.  What matters is how much loss there is.

Good trap antennas exist.  It is possible to build trap antennas with a small fraction of a dB total loss in all the traps.    "Lossy traps" exist too, and some antennas are built with those, but largely the idea that "traps are lossy" is an antenna marketing tool, not physical reality.

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

Trust me, the HF6V has matching system losses as well.  I think it is a good design that keeps losses low.  But there are antennas with traps recognizable as traps that also keep system losses low.  So we shouldn't be insisting that "traps are lossy" or "coils are lossy" or "stubs are lossy" or whatever without qualification.   That's a great marketing trick but doesn't help us understand which antenna is best.

There are good trap antennas and bad trap antennas.  The best way to tell the difference is to make a controlled field strength measurement, and that's probably the only way to tell the difference between a couple antennas where one is 3 or 4dB lossier than the other.  And 3 or 4dB is already in "danger" territory for a trap vertical that's rated for QRO that only has "lossy traps" to burn that extra power, because then the traps have to dissipate half or more of the 1500W rating.  I doubt such an antenna would survive long in eHam ratings without getting a "0/5 burned up" or several.


 
73
Dan 


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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AL7AW
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« Reply #11 on: March 05, 2010, 11:37:21 AM »

I is usually easier to construct radials at ground level.
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SV1BDO
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« Reply #12 on: May 06, 2010, 04:48:23 AM »

I am building a homebrew Butternut HF2V (30m included) and I plan to install it in a few weeks on a top of an almost square tarace (aprox 12mX14m) on a 4 story building, but not in the middle of it, but about 3m away of the center.   

I am concerning about elevated installation of the feeding point on an insulated fiberglass pole at aprox 2-2,4m. I plan to install about 40 radials, but few of them will be resonant for the 40m band and the others will be shorter or longer. Most radials will be from thin solid chicken wire and few of a little thicker insulated copper wire (used in house hold installations).

I was searching for information about this kind of installation and the most relative I found is Rudy's N6LF article in QEX (mentioned in this post). My installation will be like the one described in "Part 7, Ground Systems With Missing Sectors, Fig 2, C9" of his article.

So my questions are:
a) The height of feeding point is critical or not?
b) Is there any need for the radials to be resonant for a given band (40m), or the antenna will perform better with as much more radials as I can install, even though some of them will be longer or shorter than resonance?
 
Thanks & 73,
Sotiris SV1BDO
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WX7G
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« Reply #13 on: May 06, 2010, 09:12:05 AM »

If you are saying that the feedpoint will be 2 meters above the radials that is a problem. The 2 meter mast lengthens the radiator by 2 meters and will detune the antenna. If the radials are attached at the top of the 2 meter mast (at the base of the antenna) it will work.

I believe you will need resonant radials; two or more per band arranged symmetrically will work. The symmetrical configuration greatly reduces radial radiation. The radials can be bent to fit the available space as long as they are not bent at greater than 90 degrees. A 1:1 choke balun at the feedpoint will ensure that the radials carry most of the counterpoise current and not the coaxial feedline shield.
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WB6BYU
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« Reply #14 on: May 06, 2010, 09:49:56 AM »

For elevated mounting on top of a building, the radials should be resonant.  If you are planning
to operate 20, 30 and 40m, for example, you would want to use 4 radials that are quarter
wave resonant on each band (a total of 12 radials) instead of random lengths.  You can use
more or less radials, but the ones that are a quarter wavelength long are the ones that are
most important on each band.

The radials must be attached right at the feedpoint to the antenna, not at the base of the
mast it is mounted on.  Otherwise the mast must be considered as part of the antenna, and
the shield of the coax is no longer connected at a grounded point, so it will be more prone
to common mode current.
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