Verticals

[KX5JT]

Hi everyone.

Over in the QSO section under the WFEA and the Blaw-Knox 160 meter experiement post, Don, K4KYV stated the following:

"The purpose of the ground plane or counterpoise is to isolate the radiating element of the vertical from the lossy earth.  It the case of a Marconi type antenna, the ground system is also part of the antenna's resonant circuit.

It is a common misconception that no ground system would be needed for a ground mounted half wave vertical.  Yes it would resonate, but 80% of the rf power would be wasted  heating the soil in the vicinity of the antenna.  So a radial system is still needed, even if the length of the vertical is such that it may be made self-resonant.

The closer to ground the base of the antenna is, the more radials are needed to effectively shield the lossy earth from the antenna.  A ground mounted vertical needs at least 60 quarter wave radials.  OTOH, a VHF ground plane mounted many wavelengths above ground needs only 3 radials.  At intermediate distances, more radials are needed, but not so many as are needed for the ground mounted vertical.

Some broadcast stations have successfully been able to use an elevated ground radial system, high enough off the ground to allow farm equipment to operate under the ground plane.  They can get by with fewer than the standard 120 radials.

The commercially made ground mounted "no-radials-needed" amateur radio verticals are a bogus ripoff.  The sales pitch would suggest they are able to violate the laws of physics.  Better to save your money and construct a real vertical.
"

I wanted to open a discussion about the verticals.  I know the ground-mounted ground plane antenna is very attractive for the lower bands, however I am considering going with an elevated multi-band vertical for the higher bands.  I'm actually considering the HyGain AV-640 ]http://www.hy-gain.com/Product.php?productid=AV-640 due to the very fact that it doesn't require a conventional radial system.  The idea is it is made up of basically what amounts to centerfed vertical dipoles (using tuned stubs and capacitance hats).  I know that this completes the antenna as fas rf ground but what about ground losses?  I live only 30 someodd miles from the Gulf of Mexico on what was once brackish marshes and the ground conductivity on my property is naturally very high.

Is this type of vertical a POS or is it maybe the exception to not having an actual ground plane in copper/aluminum?

KX5JT

[K1JJ]

Hi John,

Here's a summary of ground radial info I got from the 160M vertical gurus a few years back - in case you didn't read it.

http://amfone.net/ECSound/K1JJ16.htm



and more :

http://amfone.net/ECSound/K1JJ11.htm

T

[k4kyv]

Hi John,

Here's a summary of ground radial info I got from the 160M vertical gurus a few years back - in case you didn't read it.

http://amfone.net/ECSound/K1JJ16.htm

An excellent treatise.  One suggestion, though...

15) When connecting interlaced radials together, bind with wire, solder, then tape real well and then coat with RTV or some good weatherproofing compound. The solder will fall apart into a white powder if exposed for long in the soil without protection. If sealed off, the sealed insulated wire will keep the copper inside bright and shiny for years...sealed against water and soil contaminants.

Better still, use silver alloy brazing rods, available at any plumbing supply. Not dirt cheap, but not unreasonably expensive, either.  This is what the plumbing code now requires for soldering copper water pipes together.  The use of lead/tin solder is a no-no due to the possibility of lead leaching into the water, plus the minerals in the water will cause the same white powder effect, eventually leading to leaks.  You need something hotter than propane to melt the solder; I use a Mapp gas torch.  Heat the copper to a dull red glow (careful - it's easy to get carried away and melt the copper wire) and the solder flows on without any kind of added flux.  Just make  sure there is no scaling crud on the copper. The heat will burn away anything else, and the copper soaks the stuff like a sponge soaks up water.  I silver soldered my radial system together in 1983 and the joints are still intact.  Lead/tin turns to powder in this soil in about 30 days.  I wouldn't trust using it, even when covered with what appears to be a good sealant.

A lot less hassle and expense than Cad welding, as long as you can heat the copper to the required temperature.  I have successfully brazed to copper clad ground rods by digging down so that about a foot of rod is completely exposed, to keep the soil from heat-sinking away the torch heat.

[Steve - WB3HUZ]

Some good basics on verticals.

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=14925

[KX5JT]

What about the case of a vertical dipole... where you have balanced antenna that is oriented vertically?

Thoughts on these?

[k4kyv]

WWV used to use those when the station was located on the east coast.  Verticals were mounted on wooden utility poles.  Should work OK if the whole thing is high enough that the bottom end is raised well above the ground.

If the bottom end is near the ground, per the discussion in the other thread, ground losses would be excessive unless a radial system was installed.

[K1JJ]

What about the case of a vertical dipole... where you have balanced antenna that is oriented vertically?

Thoughts on these?

Yes, vertical dipoles and vertical dipole arrays generally need good ground systems or "ground screens".  No free lunches. They are vertically polarized and need support just like any vertically polarized stick.

Take a look at the huge vertical log periodic TCI broadcash arrays that are hung vertically. They recommend an extensive ground screen.


As the dipole slopes more towards horizontal (the sloper) the requirements for a ground screen get reduced until a fully horizontal dipole requires very little to no screen. This requirement for horizontal dipoles further diminishes as it gets higher approaching 1/2 wavelength above ground.

At one point I tried about every 75M DX antenna known to man. The biggest vertically polarized one was a series of veritical dipoles in a line (7 elements) towards Europe. It looked great, but performed poorly due to my poor Earth soil - big losses. I rotated them to horizontal dipoles and picked up 15db and it became a good performing directional antenna.

People with salt water, marsh, exceptional soil or extensive ground screens might do well. I know of a few in Europe that do well. EI4FC is one that comes to mind using a line of vertical dipoles over that rich Irish soil.  He wud sometimes pin my meter on 75M in the wintertime.  I don't recall if he used a ground screen too - I'll axe him next time.


T

[KX5JT]

People with salt water, marsh, exceptional soil or extensive ground screens might do well.

That's the idea here.  The marshes start about 10 miles south of me.  This area has very high ground conductivity and very rich fertile soil that no doubt was part of the marshes at some time in the geological past.  Presently there is 60 acres directly behind me flooded for rice production.  (Some of that is actually on my property, the rest is the adjacent family property)   That AV-640 by HyGain is basically a multi-band vertical dipole.  I will mount it above the metal roofing and other structures.  (The metal structures on my property is the reason I don't want to go ground mounted, besides this is for the higher bands anyway)  I suppose there's one way to find out how good it plays......*grin*

KX5JT

[flintstone mop]

If space is a problem for 120 radials go for elevated radials. Fewer becomes better.
But now you have to watch out for lawn mowing in your lawn tractor or hunters during the Winter months, where the deer and the antelope play

Fred

[k4kyv]

If space is a problem for 120 radials go for elevated radials. Fewer becomes better.

But now you have to watch out for lawn mowing in your lawn tractor or hunters during the Winter months, where the deer and the antelope play

With elevated, also the higher the better. Run the radials about 7' off the ground.  People and lawn tractors can easily pass under them.  You can even use the acreage for a nice vegetable garden underneath. To make up for the lost height, add a 7' whip to the top of the tower.  An old fashioned full-size chickenband mobile whip should be perfect.

The deer and hunters just have to fend for themselves.  I use #8 copperweld for my beverage, and I doubt even an elephant could easily break the wire.  If a deer gets hung up in the wire, all I have to do is temporarily zap the antenna with the output from a spare 7.2 kv pole pig.  That would be one way to take care of those damned pests.  It would save the hunter the cost of a bullet.

[WU2D]

I have had great luck with only 4 radials on 75M verticals and elevated them at 7 feet so I could walk under. Of course more is better but 4 is a start.

MIke WU2D

[W8EJO]

Consider a center fed inverted L. I  use an 80' x 90' version as an allbander @ my MI cabin with excellent results on 160 - 20.

Bottom of vertical section is about 8' off the ground - no radials. L.B. Cebik did extensive modeling of this antenna  both with & without radials & found no adavantage to adding radials.s

Unfortunately, after his untimely death, his web site went commercial. It was a veritable cornucopia of antenna knowledge.

Terry
W8EJO



 
 

[KB2WIG]

http://www.cebik.com/


It's comercial, but all the old info is there, and there's no charge to use it.... just  register and go....

klc

[K6JEK]

I have had great luck with only 4 radials on 75M verticals and elevated them at 7 feet so I could walk under. Of course more is better but 4 is a start.

MIke WU2D

There is an excellent series of articles about verticals and radials in the recent issues of QEX. Rudy Severens, N6LF, did meticulous field tests of verticals with various radial configurations.  One of the most interesting conclusions is that just a few elevated radials are as effective as many on ground or buried radials.  For example, four 1/4 wavelength radials 4' off the ground are within  .1 dB of 64 on ground radials.  Also interesting, the radials can be as low as 1' off the ground and still be almost as effective and alternate geometries like gull wing and sloping radials, 1' up to 4' are just about as good.   His measurements confirmed NEC models.

I recommend getting your hands on the March/April QEX before you start putting a bunch of wire down.

[KX5JT]

[/quote]
There is an excellent series of articles about verticals and radials in the recent issues of QEX. Rudy Severens, N6LF, did meticulous field tests of verticals with various radial configurations.  One of the most interesting conclusions is that just a few elevated radials are as effective as many on ground or buried radials.  For example, four 1/4 wavelength radials 4' off the ground are within  .1 dB of 64 on ground radials.  Also interesting, the radials can be as low as 1' off the ground and still be almost as effective and alternate geometries like gull wing and sloping radials, 1' up to 4' are just about as good.   His measurements confirmed NEC models.

I recommend getting your hands on the March/April QEX before you start putting a bunch of wire down.
[/quote]

ON4UN's Excellent book LOW BAND DXing also talks about the effectiveness of elevated radials compared with buried in the ground radials and comes to similar conclusions.  But again, I am talking about high band vertical and asking about the vertical dipole here, not a ground plane vertical.  I think in my case it's going to be a matter of just trying it and finding out.

KX5JT

[KL7JBB]

An admitted novice here (uh, not in the classic FCC sense)... has anyone heard of laying out ground radials in a non-radial pattern?  Some sources suggest that the radially-arrayed conductors of a vertical's ground plane may be closer together than necessary near the antenna base and too far apart further out.  I'm wondering if a series of concentric wire circles, triangles (connected by a few radial conductors to maintain electrical continuity) or even a spiral centered on the antenna base and spaced at an optimum interval might save some wire and improve the ground plane at a distance from the antenna base?  I haven't sat down to figure out required wire length... but if the ideal distance between the conductors was large enough it could save some wire and improve the ground plane's effectiveness at the periphery.

You may commence firing.

Jim
KL7JBB

[KB2WIG]

In my '74 ARRL Handbook, Jerry Sevick, W2FMI, had a 20m vertical over a modified groundplane. I'm sure theirs other stuff on the internet.

"You may commnece firing."

If they get inside of yer wire, just call in air support on yer position. You might get lucky.


klc

[KL7JBB]

No low-hanging Google fruit yet using various combinations of hf vertical, ground, radial, geometry, array, spiral, etc.   

As many others have observed, if the AM broadcasters haven't done it yet, it probably isn't worth doing.

[K5UJ]

The radial wire on the ground (or in the air or buried) should extend out straight from the driven element at right angles to the driven element so that the radials occupy a plane that is perpendicular to the vertical antenna.  I apologize for the mumbo jumbo but I am trying to be precise geometrically without an illustration.   It is better to have a direct path back to the feedpoint that is as short as possible.  So, spirals, concentric rings and so on around the antenna won't work as well.

The reason for radials is to collect RF currents and return them to the feedpoint since you don't have the other half of the antenna to do that, the part that would make it a dipole.  If you didn't have the radials you'd have earth resistance trying to do it and you'd have a nice wide 50 ohm antenna and it would stink because ground is a lousy conductor.

It might be worth trying, having fewer radials near the feedpoint and forking them.   You could try for example, putting in 30 one inch wide copper straps and let them extend out equally spaced  for 40 feet or so, then from each one run three AWG 14 solid copper wires equally spaced, each 60 to 90 feet long.  Your thirty one inch wide copper straps could all be brazed to a 6 inch wide copper strap ring around the base of the feedpoint.

But something like that is probably more laborious than simply running 90 wires all the way out.

[K3YA]

I've never heard a great signal from a multi-band vertical.  The ground losses in the radial system are an issue, but the losses in the soil beyond the radials may be a bigger issue.  For 40M and above more effective horizontal antennas are small and easy enough to install that they really need to be considered first, by my experience.

I've used vertical arrays extensively on 80M, and they can work OK for DX.  But if I had the room I would go with a really high horizontal for transmitting. And even with the verticals I always kept a low dipole up for local QSO's.  Occasionally my 80M 4-square did perform well for long hall daytime contacts, with it's low take-off angle.

I have heard one really great single vertical antenna on 75M.  OZ8BV had a vertical out over salt water  that would occasionally beat out his 3 element yagi due to it's super low take off angle.   Other then this unique situation, I think you need multiple verticals on 80M to match the performance on a high dipole, at least  on transmit.

Single verticals seem to work well on 160M , but few hams have the ability to put up a really high dipole on that band to compare it against.

[k4kyv]

The reason for radials is to collect RF currents and return them to the feedpoint since you don't have the other half of the antenna to do that, the part that would make it a dipole.  If you didn't have the radials you'd have earth resistance trying to do it and you'd have a nice wide 50 ohm antenna and it would stink because ground is a lousy conductor.

I like the way you explained that.  Simple,  clear, to the point, without a lot of technical and mathematical mumbo-jumbo

It might be worth trying, having fewer radials near the feedpoint and forking them.   You could try for example, putting in 30 one inch wide copper straps and let them extend out equally spaced  for 40 feet or so, then from each one run three AWG 14 solid copper wires equally spaced, each 60 to 90 feet long.  Your thirty one inch wide copper straps could all be brazed to a 6 inch wide copper strap ring around the base of the feedpoint.

But something like that is probably more laborious than simply running 90 wires all the way out.

If the height of the vertical is 1/4λ or less, you collect more return currents near the base of the vertical, than farther out.  You would want the maximum ground coverage right at the point where the radials are bonded to the common point.  It might be more effective to  lay down a large number of short  radials, then intermix them with fewer full length ones.  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 off 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.

The length of elevated radials will be resonant just like an antenna  element, but buried radials or radials lying on the ground have  little or no resonant length effect; any convenient length will be effective, but there is a rather complicated trade-off between lengths and numbers, for a given amount of copper.  A few very long radials is little more effective than the same number of short ones (some calculations suggest that four long radials may be less effective than four short ones) , and in any case are less effective than a large number of short wires.  But once the space near the base is filled in with a large number of short radials, their effectiveness increases as they are made longer. It's like you have to fill in the area near the base with copper before adding additional copper farther on out is much of an advantage.

[N7BDY]

Don,   I agree that fewer elevated radials are the way to go , at least in my experiance with verticals . 

However I'd like to put something up more temporary for the moment , and I have enought stuff onhand to put up a ground mounted 40 meter vertical .  You mentioned ground mounted verticals shorter than 1/4 , the radials work just as good up closer to the vertical component .  What do you think of  ground screens for a 40 meter vertical ?  A 100 foot roll of chicken wire is pretty cheap and I could get 4 x 25  screens out of a roll  ( or more ,  I can get a couple rolls  )  .  I live where I dont have to worry about tripping over it etc   ( rural desert covered with scrub ) and I could easily throw dirt over the screen too to tidy it up once its all tuned up  .  Seems like an easy way to get a vertical up without a lot of work .  No worry about cutting them to resonance either .   There isnt much corosion here , too dry .  Galvanize would last longer than I'd ever keep it up .

Ever try that method for a down and dirty temporary setup  ?   Eventually I want to put something else up ,  but for right now .........

n7bdy
Bob

[W1VD]

I use 50' and 100' runs of chicken wire to augment my regular wire radial system on the 137/500 kHz 90' top loaded vertical here. Works well. Soldered #14 stranded THHN 'pigtails' to the ends of the chicken wire for a good connection.

Avoid the common pitfall of shooting for a 50 ohm match. Keep adding radials while monitoring the antenna R ... as you add radials the antenna R will be driven lower and lower indicating that more return current is being collected. When adding additional radials no longer drives the R lower, you're done. At that point add a matching network (a simple L network will usually suffice) to match the antenna impedance to the 50 ohm feedline.

         

[W8IXY]

Regarding elevated radials, as used on broadcast station verticals, check this out.

http://www.nottltd.com/amgroundsystems.html


73
Ted W8IXY

[KL7JBB]

Wow.  In the right climate you could disguise the elevated radials as a vinyard!