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eHam Forums => Elmers => Topic started by: K9BAY on August 21, 2010, 06:33:13 PM



Title: Vertical Antenna Mounting Considerations
Post by: K9BAY on August 21, 2010, 06:33:13 PM
I am getting ready to put up a vertical antenna (40 - 10M).  I am contemplating whether to ground mount it using ground radials (16-32 required) or mount it elevated (4 elevated radials required, 45 degrees inverted V from the base of the radial connection to the feedline) on a tripod.  I was wondering based on actual experience, if there is any performance gain one way over the other (ground vs elevated).  I would think having the antenna elevated would be an advantage.

Where I can mount the vertical on the ground using ground radials, I will have obstacles. I may not be able to provide a complete 360 degrees radial pattern. Probably 270 degrees at best.  With the vertical elevated, I feel I have plenty of room for the 4 radials  North, South, East, West approx directions.

As far as radial length, ground at least 26 - 30 ft radials are recommended.  I have read where radial lengths over 20 ft don't provide any additional performance benefit.  I assume the same for the elevated in an inverted V configuration.

I would really like to hear from those who have used both vertical configurations (ground mounted vs elevated).  Or particularily those who have used an elevated vertical antenna.   I am also interested interested in susceptibility to lightning (since vertical is elevated) the best way to ground and protect the antenna from potential lightning strikes.

I am looking forward to real life experience feedback.

Thanks!


K9BAY


Title: RE: Vertical Antenna Mounting Considerations
Post by: WB2WIK on August 21, 2010, 09:06:09 PM
Elevated, with tuned radials (1/4-WL long each, 3-4 per band) is better.

I currently have, besides beams and wires and other stuff, a simple 6BTV vertical on a small roof tower at about 28' above ground with 24 tuned radials under it.

It's a pileup buster.

On the "lower bands" like 80m-160m this is really hard to pull off and ground mounted with lots of radials is the norm.

But on the "higher bands" like 40m and "up," in my experience the elevated vertical with just 3-4 1/4-WL radials almost always works better (and I've tried dozens of times, from about 15 different homes).


Title: RE: Vertical Antenna Mounting Considerations
Post by: K1WJ on August 22, 2010, 05:25:51 AM
If you ground mount the antenna you can put as many & as long radials as needed to fit. Put the antenna in the clear as much as possible. The ground mounted radials can be any length that works for your location. I would make some 8ft at the shorted & as long as 33ft. Try to have at least 16 radials if you can.
If elevated off the ground you will need minimum of 2 per band - 4 per band would be ideal. So for 10-40m you will need 8 radials minimum - 2 for each band. An elevated vertical with 2 radials per band would equal about 32 ground radials for ground mounted generally speaking.
Ground mounting is easy vs elevated because you do not have to tune the radials like an elevated vertical.

I've been running a 4BTV ground mounted with 32 radials for about 4 years now. I've also added 12m & 17m by running 1/4w wires parallel to main element - easy.

73 K1WJ David 8)


Title: RE: Vertical Antenna Mounting Considerations
Post by: W8JI on August 22, 2010, 06:15:14 AM
You will get quite a few opinions on this, and I've measured both as best I could. In truth, the accurate answer depends on many things.

My opinion is on higher frequencies like 20 meters and higher you are better off elevating the vertical in MOST typical locations. This is because height gets the antenna above ground clutter like fences, houses, and other objects. Height also reduces ground losses by reducing field intensity at earth surface.

On lower bands you are better off with a grounded vertical. There have been very accurate measurements that have shown eight elevated radials about 1/4 wave high are equal to a big ground system on the ground. The problem is on 40 meters or lower, resonant radials have to be 1/4 wave long.

Another problem is common mode current. Four radials are NOT a perfect ground, and do NOT have zero impedance. You can see how much feedline shield current there is here:

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

Don't let anyone tell you four resonant radials makes a perfect unbalanced system. It does not, and I have proved this time and again in measurements.

The real choice is mostly mechanical, because either system will work with pro's and con's.

The elevated system, if you can get enough height to clear surroundings and enough radials, will work a little better (especially on higher bands). You would have to decouple the feedline shield and could have lightning issues because the common point of the radials cannot be earth grounded if you want maximum performance.

The earth mounted system would be lower maintenance, better aesthetically, and not have so many lightning and common mode problems. The radials would also work on ANY frequency with no need for special radial lengths. just as many as you can as long as you can, with little need to have more than 20 or so. It would not do as well on fifteen or ten meters unless you have a clear area.

The choice is really yours, because each has advantages and disadvantages and each will make nearly the same contacts.

73 Tom






Title: RE: Vertical Antenna Mounting Considerations
Post by: K9BAY on August 22, 2010, 07:28:29 AM
Thanks for the replies thus far.  The antenna manufacturer recommends 4 radials but I am finding out that 8 radials are a minimum.  This leans more toward the ground mounted anteanna.  For an elevated, I was hoping to achieve this with 4 radials inverted V all ending at the as close to a ten foot line in the trees surrounded (feed by nylon rope to maintain seperation from the trees themselves). Adding another 4 radials, depending on how far apart they are spread, will instill the laundry line look in the backyard.  I may be able to get away with 4 radials, but 8 may be a stretch. 

My plan was to set the elevated vertical up for the late fall (post mowing season), winter, spring (pre mowing season). As accessability to the yard for mowing, etc is mute. Then convert it to a ground mounted vertical stringing ground radials several weeks prior to mowing season starting.  Thunderstorms in the late fall, winter, and early spring are vary rare.  If the elevated system is guyed down securely, I think the only issue maybe ice.  I don't know how ice buildup on a vertical impacts performance.

I may be able to keep the elevated vertical in place if the end points of the radials are elevated 8-10 above the ground.  The term "temporary" makes the XYL more agreeable to see how various vertical configurations work. 
As transparent as possible, the goal.  I started out with a Buddipole in the back yard on a tripod and transitioned to a 20M dipole hung in the yard.  So I am slowely transitioning to larger antennas.
 :)

Thanks!

K9BAY


Title: RE: Vertical Antenna Mounting Considerations
Post by: K3GM on August 22, 2010, 08:10:56 AM
.....Don't let anyone tell you four resonant radials makes a perfect unbalanced system. It does not, and I have proved this time and again in measurements......

Tom, you once said something like "if you could measure the current flowing in the radials versus earth, you'd see that 4 radials are insufficient".  Is this something that can be done with average shack equipment, and how do you go about setting up the test?


Title: RE: Vertical Antenna Mounting Considerations
Post by: N3OX on August 22, 2010, 10:01:05 AM
Thanks for the replies thus far.  The antenna manufacturer recommends 4 radials but I am finding out that 8 radials are a minimum.  This leans more toward the ground mounted anteanna.  For an elevated, I was hoping to achieve this with 4 radials inverted V all ending at the as close to a ten foot line in the trees surrounded (feed by nylon rope to maintain seperation from the trees themselves). Adding another 4 radials, depending on how far apart they are spread, will instill the laundry line look in the backyard.  I may be able to get away with 4 radials, but 8 may be a stretch. 

My personal preference is to use a ground mounted antenna for the lower bands where houses and other obstacles should be a bit  more transparent, and cover the higher bands using horizontal antennas as high as I can get them.  It doesn't take that much height  over regular dirt to have a dipole equal to or significantly better than a vertical, even if the vertical was elevated... if I can get a horizontal antenna up at least a half wavelength, I don't even think about a vertical for that band, basically.

My horizontal antennas are all rotatable, so that's a consideration, but it's pretty easy to make a simple, cheap rotatable antenna... I used to run a 17m loop antenna built like this:

http://n3ox.net/files/17loop.jpg

Subjectively speaking, with the loop bottom only 6 or 7 feet off the ground (top at maybe 25 feet) ,  it beat the pants off of my 17m ground plane with radials up about 8 feet.   That won't necessarily predict what that kind of thing will do for you, because a simple model shows that the vertical should actually be a tad better at very low angles than the loop (the loop is much better above 10 degrees elevation).   

 In my particular tests, the rotatable loop was much, much better even for very long haul stuff.   It was so much better that it's suspicious.   Nevertheless, I did a lot of tests over maybe a year or two and always found the horizontally polarized loop to be better.  I was really curious to do a lot of tests because I was new and everyone was saying "verticals are better for DX" and that was blatantly untrue for my particular circumstances.    I wish I could go back in time and slap a current meter on the vertical's feedline because I suspect something was wrong with it given the outcome.

I've tried other monoband elevated verticals and even things like half squares (two phased) vs. reasonable height horizontal dipoles, etc, and I've never been impressed with "verticals for DX" over ordinary dirt on the high bands.  The verticals work "fine" but the horizontal dipoles really work better.  Not as dramatically as my loop vs. vertical on 17m, but generally better. Theory backs that up: you get more advantage from ground reflections over ordinary dirt when you run reasonably high horizontal antennas.

The other thing to consider is that a random length radial field on the ground can be used with ANY vertical you ever want to try without changing anything.  When I decided to change from a 40 foot vertical to a 60 foot vertical to get better results on 160m, I didn't have to do anything to the radials because I'd already filled my yard full of them.    If you wanted to add 30m and 17m to an antenna that didn't have them before, you wouldn't have to change anything... that's not true of elevated, resonant systems. 

So all in all, I like ground mounted verticals and I just use horizontal antennas where a ground mounted vertical might be a poor performer.  If you're not restricted to one antenna, I'd maybe recommend that, or at least experiment with it.


73
Dan



Title: RE: Vertical Antenna Mounting Considerations
Post by: K9BAY on August 22, 2010, 10:38:31 AM
Thanks, I am hoping to hear from some other hams with elevated vertical antenna experiences.

So a ground mounted vertical is leading.  But I think having the antenna higher in the air, would make a difference.  So far there is no evidence to elevated is better.  It is quite a bit of work to run the radials for either ground or elevated.  I really would like to test the elevated and see.  I realize EVERY antenna in its own environment is different, and has its own footprint.

Thanks!

K9BAY


Title: RE: Vertical Antenna Mounting Considerations
Post by: N3OX on August 22, 2010, 01:35:02 PM
 So far there is no evidence to elevated is better. 

I've never had equivalent verticals ground mounted and elevated at the same time, but I guarantee you that in a typical suburban backyard, a vertical up high enough to clear the "ground clutter" of surrounding houses, sheds, cars, etc, has a very good chance of showing a measurable advantage on the higher HF bands.  And even elevating some will help the blockage due to obstacles. 

Elevating gives a bit of ground reflection  gain if ground loss is held constant.

But if you're not talking about significant elevation to clear surrounding stuff, you get into a situation where the advantages won't be clear.

Quote
Thanks, I am hoping to hear from some other hams with elevated vertical antenna experiences.

All of the "ground plane" antennas I was talking about were elevated.  That's what I mean when I say "ground plane."  I call the one on the ground a "ground mounted" antenna.    My old QTH was my parents' house back in high school, I installed many verticals but never put down ground radials for a ground mounted antenna because it seemed like too much work compared to just having a few 1/4 wave wires above ground.  They didn't mind a lot of wires in the air, but I didn't want to dig up the lawn (this was before I discovered the "lawn staple" method)

At the old QTH I also had a 40m 1/4 wave with four radials elevated about 16 feet and I was very happy with that antenna, but there's not much point in talking about it with respect to the other 40m antennas I've used, because they were in different states at different parts of the sunspot cycle ... I didn't have a ground-mounted vertical to compare the elevated 17m and 15m and 12m antennas to, but at least I had SOMETHING to compare on the higher bands :)

In the end, how much elevating matters is something that only YOU can find out.  No one else's advice about their antenna's environment will apply very well to your situation.    And to get a real answer, you have to install BOTH antennas separated by enough that they don't interact and then you need to A/B test them for a year.   Almost no one does that.... so keep that in mind when people tell you "I didn't have any other antennas but my elevated GAP vertical was great"

;D

This is especially true if elevating can get you out above nearby obstacles... no one can ever tell you if the neighbor's house is blocking your radiation... you just have to test it.  On 80m, where your neighbor's house is a little 1/8th wavelength tall "bump," you can be pretty certain it can't do any significant damage to your pattern.  On 10m where it's a wavelength tall and a wavelength or two wide, it could cause trouble.  But it might just happen to be more or less transparent to radio waves...

It won't hurt to try the elevated antenna... higher IS better.

73
Dan


Title: RE: Vertical Antenna Mounting Considerations
Post by: K9BAY on August 22, 2010, 02:12:45 PM
Thanks Dan,

I think I am going to test for about a few weeks or so with the vertical elevated using 4-8  radials, and see how that works.  If it doesn't work out, I can move it over to a ground mount with ground radials.   I will probably just pound in the ground mount and have the radial plate ready to go.  Because I am not mowing, I can string the radials quickly and just tack each down in a few places with fabric staples.    Then I can check at pre-spring time and decide to bury them.  Going through a fall / winter season, the ground radials may just need some additional meshing and tacking to get them clear of the mower.

Dan, a couple of questions.  Did you run your elevated radials on a 45 degree slope all the way to the ground?  Can the radial endpoints also be elevated so they are above human height and not an obstacle themselves?

Thanks again,

73 K9BAY


Title: RE: Vertical Antenna Mounting Considerations
Post by: N8CMQ on August 22, 2010, 04:44:13 PM
I am getting ready to put up a vertical antenna (40 - 10M).  I am contemplating whether to ground mount it using ground radials (16-32 required) or mount it elevated (4 elevated radials required, 45 degrees inverted V from the base of the radial connection to the feedline) on a tripod.  I was wondering based on actual experience, if there is any performance gain one way over the other (ground vs elevated).  I would think having the antenna elevated would be an advantage.

Where I can mount the vertical on the ground using ground radials, I will have obstacles. I may not be able to provide a complete 360 degrees radial pattern. Probably 270 degrees at best.  With the vertical elevated, I feel I have plenty of room for the 4 radials  North, South, East, West approx directions.

As far as radial length, ground at least 26 - 30 ft radials are recommended.  I have read where radial lengths over 20 ft don't provide any additional performance benefit.  I assume the same for the elevated in an inverted V configuration.

I would really like to hear from those who have used both vertical configurations (ground mounted vs elevated).  Or particularily those who have used an elevated vertical antenna.   I am also interested interested in susceptibility to lightning (since vertical is elevated) the best way to ground and protect the antenna from potential lightning strikes.

I am looking forward to real life experience feedback.

Thanks!


K9BAY


Hi!
 You should read QST in the 71 to 75 range, by Jerry Sevick... He did a great job on vertical antennas, and they should have been turned into a separate book by the ARRL...
 To post script it all, a ground mounted vertical needs as many and as long a radial as you can install. And a ground mounted vertical will outperform an elevated vertical with four radials per band...
 And I proved it to myself. I placed a 4BTV in the center of my back yard with 100 radials going to the edges of the backyard. This was a roughly 60 foot square, so each radial was 30 to 35 feet long, both copper and aluminum wire was used. It was a DX magnet, and a net master!
 My XYL did not like the antenna and demanded it be removed... It was acceptable to her to have it on the roof. I installed it there with 4 radials per band, but it did not match the performance of it on the ground, even though it was 15 feet higher in the air, and above the aluminum siding of the surrounding houses... After the divorce, I was able to ground mount it again, but I did a mod Dr. Sevick mentioned in one of his articles...
I have restored this antenna, and have reinstalled it at my present location, I have 125 radials under it, and even though it is 40 years old, it still performs very well! Friday, 8-20-10, I listened to a gentleman in Ireland talking to people in Japan, on 20 meters at 6:30 AM... Check out my Blog at www.myspace.com/n8cmq


Title: RE: Vertical Antenna Mounting Considerations
Post by: VA3GML on August 23, 2010, 09:50:51 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.


Title: RE: Vertical Antenna Mounting Considerations
Post by: WA1RNE on August 23, 2010, 10:32:21 AM
Thanks, I am hoping to hear from some other hams with elevated vertical antenna experiences.

So a ground mounted vertical is leading.  But I think having the antenna higher in the air, would make a difference.  So far there is no evidence to elevated is better.  It is quite a bit of work to run the radials for either ground or elevated.  I really would like to test the elevated and see.  

 You should try an elevated vertical at least once, but like most antennas, certain systems provide better performance.
 I've had some very positive experiences on 75/80 using a top loaded 36' vertical with 4 elevated radials. IMO, the bottom line is minimizing ground losses as well as maintaining a clean pattern. The key to minimizing ground losses with a low HF band elevated installation is maintaining a minimum height above ground as well as insuring proper radial length. My system maintained 0.05 wavelength above ground, which on 75 is about 13' (about 7' on 40). I used a current balun at the feedpoint which was approx. 30 turns of RG-8X close wound on a 4" PVC form. At 36' tall, 100% top loading and an L network to match the ~28 ohm feedpoint impedance to a 50 ohm line, the antenna performed extremely well, and allowed me to break through pileups on the 75 meter DX window regularly. Total cost: about $75.


Title: RE: Vertical Antenna Mounting Considerations
Post by: N3OX on August 23, 2010, 10:52:02 AM
Dan, a couple of questions.  Did you run your elevated radials on a 45 degree slope all the way to the ground?  Can the radial endpoints also be elevated so they are above human height and not an obstacle themselves?

The elevated verticals I've used have all had the radial tips well above human height.The 40m vertical had no slope at all... 15 feet or so on both ends.  The others had a little slope but never 45 degrees... it improves the match, but I don't think it's worth trading off safety and convenience for that... plus, it's important to keep the tips reasonably above ground for loss reasons too.  There's strong electric field around the tips, and you don't want that shoving around electrons in the dirt !

The 40m vertical was something like 30-35 ohms which shouldn't pose a problem in most circumstances.  I had a slightly weird issue that needed a transformer for that antenna, but it was just because I accidentally buried some nice 75 ohm RG-11 over to the antenna, not realizing it wasn't RG-8, and didn't want to dig it up  ;D

73
Dan



Title: RE: Vertical Antenna Mounting Considerations
Post by: M5AEO on August 28, 2010, 03:12:35 AM
I have a helical vertical mounted on my balcony at about 55 feet agl, with 10 tuned radials undneath.  It just about works on 40m, but works very well on frequencies above 10mHz.

Jon, M5AEO, London.


Title: RE: Vertical Antenna Mounting Considerations
Post by: K9BAY 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.


Title: RE: Vertical Antenna Mounting Considerations
Post by: W9OY 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.


Title: RE: Vertical Antenna Mounting Considerations
Post by: W9OY 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


Title: RE: Vertical Antenna Mounting Considerations
Post by: W4VR on August 28, 2010, 10:50:28 AM
Elevate it.  You'll get better results.


Title: RE: Vertical Antenna Mounting Considerations
Post by: WA1RNE 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 (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 (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


Title: RE: Vertical Antenna Mounting Considerations
Post by: K9BAY 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


Title: RE: Vertical Antenna Mounting Considerations
Post by: WA1RNE 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.


Title: RE: Vertical Antenna Mounting Considerations
Post by: K9BAY 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


Title: RE: Vertical Antenna Mounting Considerations
Post by: W5WSS 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


Title: RE: Vertical Antenna Mounting Considerations
Post by: W8JI 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















Title: RE: Vertical Antenna Mounting Considerations
Post by: K9BAY 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.




Title: RE: Vertical Antenna Mounting Considerations
Post by: WA1RNE 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.
 


Title: RE: Vertical Antenna Mounting Considerations
Post by: W8JI 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


Title: RE: Vertical Antenna Mounting Considerations
Post by: K9BAY 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





Title: RE: Vertical Antenna Mounting Considerations
Post by: K2QPN 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


Title: RE: Vertical Antenna Mounting Considerations
Post by: AG4DG on September 09, 2010, 01:30:35 PM
For a multiband antenna, I think it's better to use a ground-mounted antenna, because you don't need to be concerned about radial length.  The trouble with an elevated multiband antenna is that you may get resonances that you don't want on the higher bands, and this means more high-angle radiation that never gets refracted downwards.

Another possibility is to have two antennas instead of one for 10m-40m.  One antenna can be a single-band 10m or 40m antenna with elevated radials while the other antenna is a multiband antenna with ground radials.


Title: RE: Vertical Antenna Mounting Considerations
Post by: N3OX on September 09, 2010, 09:17:18 PM
Quote
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

Manufacturer instructions and antenna reviews don't mean anything in terms of signal strength.

Manufacturers tell people what they want to hear and/or don't take the time to really understand antennas.  This is especially true in today's antenna market where you can read all over the internet how happy everyone is with things that radiate between 1% and 50% of your applied power.  A lot of people who are end users of antennas like the popular untuned verticals don't ever take the time to compare.  After all, they're looking for cheap and easy.  There's nothing wrong with looking for cheap and easy and discovering that it's good enough for you.

But by far, the best bang for your buck in antennas is not a product.  It's antenna theory or experimentation, or both whichever suits your skills and interests more.   If you look toward theory, you should go for reliable sources and make sure that the predictions actually work, so you don't just believe some smart sounding guy with dumb ideas.   And when you do experimentation, you need to be really, really doubtful that you can get the right answer, and test until there is no more room for doubt.  It's too easy to fool yourself when a test confirms what you wanted to see.

We need to be more honest with ourselves in this hobby.  If we want the best value for our money, we have to test and/or calculate, and probably both (as a team, not as individuals).    

If we don't really care about the best,  and just want to get on the air, we should be honest about that and not bother looking for the best.  And we need to recognize that an antenna that wastes 75% of the applied power is probably just fine for all sorts of hams... but in no way can it be considered the best thing that could be done in most situations.

 I think antenna reviews screw up people's decision process, making people think bad things work well and making them waste money.  Don't forget that after you've been disappointed by three $140 antennas, you've paid for a $400 antenna... plus you can probably get a good trap vertical used for that price or less.