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Author Topic: Verticals  (Read 27951 times)
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K5UJ
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« Reply #25 on: May 01, 2012, 09:33:15 PM »


I like the way you explained that. 

thanks Don


A common practice at broadcast stations in the past was to  lay out a  ground screen near the base of the tower, but I have read that it was later determined that the ground screen produces little or no improvement;

copper mesh is still put down but I've only seen it used in the immediate vicinity of the base pier.   I think the problem with mesh is (for lack of a better term) eddy currents.  I probably am not calling them the right thing but I hope you get the idea.  discrete radial wires don't have that problem. 
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« Reply #26 on: May 01, 2012, 11:55:39 PM »

Does all of this conversation mean that a vertical used only for receiving also needs radials? Or it it just for transmitting?
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« Reply #27 on: May 02, 2012, 08:47:09 AM »

A common practice at broadcast stations in the past was to  lay out a  ground screen near the base of the tower, but I have read that it was later determined that the ground screen produces little or no improvement; you are just as well of with 60 to 120 radials all the way out from the base common point without a ground screen. I have seen diagrams of LF and broadcast grounds where they laid out about 120 radials to something like 0.4λ, and between them laid out more radials, at 1/8λ or less, to make a grand total of 240 or so.

A buried, copper mesh ground screen around the base of an AM broadcast monopole has been used when the monopole has high r-f voltage at its base, such as for monopole heights around 1/2-wavelength.  This can reduce the losses in that area of the earth around the tower base resulting from the higher currents there, however there can be losses in the mesh resulting from eddy currents around the attached conductors of the mesh.

The more common practice for these tower heights nowadays is to intersperse 120 x 50-ft radials with the usual set of 120 x 1/4-wave (or longer) buried radials.
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K5UJ
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« Reply #28 on: May 02, 2012, 09:53:30 AM »

R. Fry, thanks--I for one did not know that.  It did not occur to me that a high Z high voltage feedpoint would make a difference. 

Does all of this conversation mean that a vertical used only for receiving also needs radials? Or it it just for transmitting?

It's common to use short verticals only 10 or 15 feet high as receiving antennas; they have no ground system other than a wire to a ground rod if that, and are usually phased with a network to throw nulls in the direction of unwanted signals.  I think you can purchase entire kits of these things--everything you need--antennnas, feedlines, phasing network, preamps....just be prepared to spend $$$.  Often mounted on wood fence posts, they are usually spaced 40 or 50 feet from each other.
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« Reply #29 on: May 02, 2012, 11:06:55 AM »

A 4 square RX ant controller can be built with a pair of DPDT relays and 3 delay lines. It would cost hundreds of dollars.
I bought 4 Clifton labs board kits for their vertical. The metal stuff is fairly easy to duplicate.
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« Reply #30 on: May 02, 2012, 11:05:38 PM »

I'm not going to buy or make all that directional stuff. Just wondered if a ground screen or some radials under the 50FT tall vertical wire would help, but I already have a ground rod available.
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« Reply #31 on: May 03, 2012, 06:37:59 AM »

Transmitting verticals, or any that are a significant fraction of lambda on the band of interest are not great rx antennas with or without a counterpoise.  The reason has to do with S/N ratio.  A vertical can be an okay antenna but hams often don't like them because they don't know how to use them.  On 75 and 160 m. there's the classic inverted L or 1/4 w. stick with ground system.  Pretty good tx antenna but for rx a separate antenna like a small loop is almost mandatory.   Verticals pick up too much noise, especially in high pop. density areas.

What about high bands.  Joe Ham puts up a 10 to 40 m. trap vertical and says it stinks on 10 m.  But he's ground mounted it with radials.   out in the open it may play great on 40 (once again separate rx antenna may be helpful) but the part that's on 10 m. is the lowest 8 feet, so he has a 10 m. vertical lower to the ground than a hamstick on a car on a band that is much more line of sight.

Verticals for 7 mc and higher need to be elevated at least enough to clear near field objects.  just 15 feet can make a big difference.  Radials, four for each band and cut to 1/4 w. can angle down at 45 degrees with the mast to form a skirt.  Such an antenna can work well on transmit.  Since a separate rx antenna is usually necessary and it isn't hard to have a dipole at decent height, especially on 10 to 20 m. there isn't much advantage to a vertical, other than being omnidirectional.   So to me, they are useful on the low bands.     
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« Reply #32 on: May 03, 2012, 09:59:50 AM »

Lots of interesting discussion, seems to be a "religious" subject for some folks.   Personally I'm a believer in the elevated radial school of thought.

I have ran a Hygain AV-640 very successfully here in Tyler, TX for the last 3 years.   I usually win the North Texas section when I enter RTTY/DX contests running the AV-640 and an Elecraft K3.   It does have some minor issues to watch for, like the jumper that connects the 40/30/20M sections to the 15M and up parts is missing in the plans.  Also it shows a resonance on 80M which is apparently related to a static drain choke that goes up in smoke if one tries to load it on 80M Grin Grin.   All in all I consider it to be an excellent antenna, mine is mounted with the base at 22 ft.

BTW somewhere in the transition to MFJ ownership the basic design description seems to have been lost.   It is technically a collection of paralleled 3/8 wave sections sitting on top of a 4 to 1 toroidal transformer feed by a toroidal 1 to 1 balun.   The 20/30/40M sections are top loaded.  Unlike most other multiband verticals there is very little interaction between the sections making tuning pretty straight forward.

73 Jack KZ5A
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73 Jack KZ5A
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« Reply #33 on: May 03, 2012, 04:07:10 PM »

Well, since I started the thread let me chime in.  I love my elevated multiband Zero Five.  It's a bit unconventional in that it uses a 26' radiator and six 100" (5 ft) radials.  It's advertised for 40 through 10 and it does a wonderful job on those bands through my Johnson Matchbox.  There are no traps but there is a matching network at the feedpoint. 

Now of course this does not compare with directional gain antennas but it really has outshone my 40 meter inverted vee on 40 and has been a great antenna for all the higher bands through 10 meters.

A few of you out there have worked my Johnson Viking II on 20/15 and 10 meters and have usually found my signal to be well over s9.

I'm impressed with this multiband vertical.  It is not an 80 meter antenna however.

http://www.zerofive-antennas.com/10-40-meter-multiband-groundplane-freestanding-vertical-antenna
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AMI#1684
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« Reply #34 on: May 03, 2012, 06:47:38 PM »

I have a ZeroFive 43 foot ground mounted vertical with fifty, 50 foot ground radials.
It works great on the higher freqs. except 10 meters.
I use the 10 thru 40 meter ground plane like yours for 10 and 12.
I built the 80 and 160 meter base matching network designed by AD5X for the 43 footer.
I get good reports on 80 and 160 meters.
In fact most stations that I work on 160 are amazed at the signal strength I am giving them for such a short antenna.
I guess it must be the ground radials.

Don W9BHI

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KM1H
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« Reply #35 on: May 03, 2012, 09:35:43 PM »

Ive been using elevated radials on 80 and 160 for 22 years and would never go back to on the ground. In my case I have almost no ground as Im on a hill and solid rock is only inches to 2' down. The radials are about 13' high so a tractor trailer, box truck, excavator or anything else can get under them.

As Im primarily a DXer Ive over 300 countries on both bands as well as many DX contest USA wins...Id say the antennas work.

The number of radials depends upon your ground, just keep adding until there is no more change on the antenna analyzer.

Carl
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« Reply #36 on: May 03, 2012, 09:45:26 PM »

I see I've done the wrong thing. Live and learn.
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« Reply #37 on: May 04, 2012, 09:18:31 AM »

I've never owned a "storebought" vertical, but have used a few ground-mounted, and a few elevated in ground-plane fashion, all fabricated with aluminum tubing, sometimes with a base matching network.

My present (and probably permanent) location is on a Kentucky hillside with many tall trees.  (and my wife is a tree nazi so I can't cut them)  Many of these trees are 50-70 feet, substantial portions of a wavelength on 40/80/160.  And grounded on one end.  And, being very moist internally, are lossy semiconductors.  And vertically polarized. 

I have to believe that significant energy would be coupled and lost, but this is an under-researched area.  A couple of years ago, I had some conversation with Rudy Severns N6LF about this, and he dug up some very limited  information about the military experimenting with intentionally coupling to trees to use them as makeshift antennas.  Presumably due to losses, the experiments had mixed results. 

In AM broadcast broadcast, conventional wisdom advises keeping the near field clear of trees and brush, even though at those frequencies, little approaches an 1/8  wavelength.

So I have almost dismissed verticals here.  But if anyone knows of more comprehensive research that has been done on the effects of trees at hf, I'm interested.

Chris
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« Reply #38 on: May 04, 2012, 09:33:58 AM »

I'm using the DX engineering slow taper 43ft ft model with the based fed matcher for 80/160. I have a very small yard, so I'm limited to about 45 radials ranging from 15 to 45 feet. All radials were placed at ground level and held in with staples. Nature buries them for me. I find the vertical is an excellent performer on 80-15... 10 is just OK. I haven't tried 160 because the receive is just too noisy. I will be putting up a receiving loop this fall. Even though I have a small lot, I am blessed with very good soil. I think that makes up for my short radials.
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« Reply #39 on: May 04, 2012, 01:57:44 PM »

W2JRO , you mentioned you have good soil under your vertical .  That makes a lot of difference why some people have good luck with verticals and some dont and cuss them .  I live out in the desert with rocks and sand and dry as a bone ,  where you would naturally think it would be a lousy area ,  and yet the FCC ground conductivity map shows my area in northern AZ to have pretty decent conductivity .  A few guys I know get very good performance from their verticals here .  Conversely , one would think the seacoast would be a killer area for a vertical , but not neccesarily so .  In most parts of the country its only so-so ,  unless of course you are right over salt water .  Some of the prime area is dead smack in the middle of the country in that good old black loamy soil in the midwest .  I grew up in Nebraska and that whole farming area is the very best in the country .  I wish I had taken advantage of it when I was a young whippersnapper ham back then ... Grin ...Point is ,  I guess thats why some people can pound in a few ground rods and some people have to put in a lot of sweat to make a vertical come alive .  If you are blessed with good soil AND lots of wire under that vertical you have a most excellent antenna  .

N7BDY
Bob
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KX5JT
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« Reply #40 on: May 04, 2012, 02:44:55 PM »

Bob, I believe the elevated radials would be the thing do to in your situation.  Heck, from what I seen, it seems EASIER to erect 4 ten foot masts out for 4 radials that are above head level than to lay down 60 to 120 ground radials anyway...
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« Reply #41 on: May 04, 2012, 03:45:36 PM »

Hi John ,   the elevated vertical(s) would definately be the best performance wise hands down I believe .  Here is the fly in the ointment though ,  I have a 30 foot TV push up mast that I'd like to use up  (  in fact i have 2 of them ) and that sucker is heavy .  They are old and made from heavy gauge steel tubing . It would be difficult to get it up 10 feet so that I could get a tractor under it to periodically drag the ground for weeds .   The fellow I got the masts from had these 2 masts fed with a phasing harness on 40 and it was a fantastic setup .  Thats why I was leaning towards a ground screen ,  but the more I think about it , the weeds will come up through the mesh so how can I run a drag over it anyway without tearing it to pieces ?   The screen is becoming less of a good idea .  I could probably get it up 3 or 4 feet on 4x4 posts and do the elevated radials .  Thats not very high , I dont know how much interaction with the ground it would have so that they no longer look like  "elevated" radials and become more like ground radials which means more of them  .   I could make it so I could unhook the radials to drag the weeds .  4 radials isnt a big deal ,  very many more would be a pain though .  I mentioned temporary because I am putting up some buildings on the 4 acres eventually and the antennas may have to come down and moved , or something much better .  But thats not a big deal ,  I'm just thinking out loud how I'm going to do this .   I'm fortunate I have the space to do antennas at all Smiley  Ideally I'd just get some lighter aluminum tubing but I'm trying to use up the junk I have on hand .  With 2 of these things at hand I could do an "L" , a "T" ,  phase 'em , lots of choices .  I appreciate any ideas .

N7BDY
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« Reply #42 on: May 04, 2012, 07:22:26 PM »

Wow.  In the right climate you could disguise the elevated radials as a vinyard!
Yes, but you have to keep a lot of cheese and crackers in stock to fool the neighbors.
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« Reply #43 on: May 07, 2012, 01:35:23 PM »

Here is a paper as presented at the 1995 NAB Broadcast Engineering Conference.

Quote
(Elevated radials) The measured RMS efficiency was 287 mV/m... the same measured value as would be expected for a 0.17 wave tower above 120 buried radials.

They also propose an interesting idea, to shunt feed a grounded tower using one internal wire, suspended from the top of the tower at the mid-point of the tower cross-section, and fed at the bottom,  instead of the usual external skirt.

www.commtechrf.com/documents/nab1995.pdf
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