Vertical Truly Omni

[flintstone mop]

Hello All
I would like to settle my mind from an "ask the Doctor" article in QST. It was about ground radials. And a part of th answer was to "make sure that radials are completely surrounding the antenna element, if not then RF will radiate only in the direction that radials were laid."
I have some areas I may not be able to lay radials because of tall weeds. I might not have the time/energy to clear these areas out. I don't want to lay radials where they will get wacked up next Spring. I'm getting tired of doing this stuff over and over. I know the saying about 'do it once the correct way' and I won't have to return to re-do the job.
ok thanks

Fred

[k4kyv]

I'm not sure that is true.  You may get slightly more signal in the direction of the radials, but I think an insufficient number radials affects the overall efficiency of the antenna, which remains essentially omnidirectional.  The lossy earth in the vicinity of the radiating antenna simply burns up much of the rf to keep the earthworms warm instead of radiating, so you lose signal strength in all directions.

Think of the radial system as a shield to isolate the radiating antenna from the lossy earth.  If you have a good,  solid ground plane, at least 60 radials, in a 180º circle about the vertical, you will achieve better than 90% efficiency.  If the ground plane covers only 45% of the circle, only 1/8 of the ground plane will be shielded, so the losses will be much greater.  Once you lay radials every 6º or so, you can consider that sector of the ground plane shielded.  So it wouldn't make much difference whether you laid 15 radials in that 45º sector, or 120.  You would still have 7/8 of the ground plane unshielded.

But the drop off in signal  would be in total signal strength in all directions, not just in the directions where radials were lacking.

IMO, the "Doctor" was wrong.

Wonder if he also does goat gland surgery.

[flintstone mop]

Thank you DON
I never read such a clear explanation as a 'shield' from lossy Earth. It's amazing how some us non-college types, like me, ever figure things out and be able to design/repair/maintain electronics as either a hobby or business.
I have been through the "road of hard knocks" part for my background. And about 35 yrs.

Fred

[flintstone mop]

I am painstakingly rebuilding this radial system and using sod staples to hold down the wires. My past experience with this method has been that the wires will be uncuttable by next June. The growing grass in Spring will 'suck' the wires down and they will be invisible.
The next attempt, if this fails, will go to elevated radials. Too many good sig reports with the vert to abandon.

fred

[Jeff W9GY]

Where's a good place to purchase sod staples.   Menards?  Lowes?

[Steve - WB3HUZ]

I used something like these many years ago to hold down some radials. Put them in during the winter. By the time the grass began to grow in the spring, the radials were invisible.

http://hardware.hardwarestore.com/27-110-insulation-supports/24-insulation-support-wire--681747.aspx


Cut them in half and then folded them in half. I think I got them at Home Depot. I would image most any place that sells insulation would have them.

[Jim, W5JO]

Where's a good place to purchase sod staples.   Menards?  Lowes?

Some wire coat hangers that come with your dry cleaning are free and all you need do is cut them to length.

[KA8WTK]

I used the biggest paper clips that I could find and bent them into a U-shape. They were cheap. 

[flintstone mop]

If I remember it was around $40 for a thousand heavy duty sod staples.
http://www.sewire.com/sodstaples.html

http://www.petronpacific.com/sodstaple.htm
These places want oyu to request a price. I purchased these around 6 yrs ago

Fred

[K1JJ]

Fred,

Yes, Don is correct.

The radials of a vertical antenna have little effect on its pattern. The pattern of even a directional array is an omni-directional blob in the near field. The pattern is formed much after the "short" 1/4 wave radials end, thus they are not involved in pattern formation.

Radials simply return RF to the base to keep Earth losses to a minimum. For example, in salt water, all you would need is a single short wire in the water and the resulting vertical pattern would be normal and efficient, whether using a single stick or 4-square. (The salt water acts like a tremendously efficient radial field, only better)

Re-read items 1 & 2 from this treatsie on radial systems that I collected from conversations with the 160M gurus a few years back.

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

73,

T

[Ed-VA3ES]

Don't forget that once you have the requisite number of radials  to achieve your target efficiency,   you must also correct (match) for the Z and X at the feed point.   

A poor,  inefficient antenna may have a relatively low VSWR due to high ground losses. Don't be fooled by that (though I doubt that anyone on this board is that incompetant!).  I have worked with many commercial  verticals (GAP's, Butternut, Hy-Gains, etc.) and they all benefit from radials, no matter what their instruction say.   GAP's are the worst, in that they always require fiddling with the feedpoint Z and X.    Butternuts already take into account that the user will add radials, and their instructions  indicate this.

In Montreal, I had a Hy-Gain 14AVQ up at 40', on top of a flat roof. I added  more than 30 radials to this antenna, and  it worked brilliantly.     Worked loads of DX on all bands. (Of course, this was from 1973 to about 1988 or so. so we had a couple of cycles to deal with.)

 

[flintstone mop]

Ahhh Yes
I'm always out there with my trusty MFJ 259 to show me the real story. The days of running a path between the rig and looking at its SWR meter and hit and miss engineering are a thing of the past. (I have a 300 foot run to the aerial site) I am even able to tell if I need more capacitance or more inductance to get the magical 50 something ohms and a single digit Xs number.
The perfect antenna wx is here.

Fred

[W3GMS]

Fred,
Concerning the ways to keep the radials down in place, I used landscaping staples.  They are sold at various home centers.  They are like a big electrical staple without any insulation on them.  The last ones I bought were about 4 inches long.  If your familar with a place called Harbor Freigh they sell boxes of either 50 or 100 very cheap.  Home Depot sells them in their garden section and they are ususally right around where they sell the black weed control fabric. As I said, Harbor Freigh has the best price around. 
Hope that helps!
Joe W3GMS   
         

[flintstone mop]

THanks Joe and all,
I did find the box and the label where I ordered 1000 sod staples. 6x1x6 Good stuff.
Liberty Equipment, Fredericksburg Va, Don(?) 1540-898-8933, 35 lbs shipping. This has provided for several vertical antennas ground radial systems. I was probbably skimping on the number radials.
Around 35 radials is all I have patiences for, BUT I'm a little past that now, on the present system. Another S-unit from MOP RADIO.............yea sure.

Fred

[W4EWH]

I wrote to the ARRL, and asked "The Doctor" to contribute: he's given me permission to post his answer here. The Doctor's replies are in blue.

From: Bill Horne [mailto:ehorne@remove.speakeasy.net]
Sent: Tue 10/21/2008 1:42 PM
To: doctor@remove.arrl.org
Subject: Vertical antennas and number of radials


Doctor,
 
Your answer to "WA2VJLI" in the October 2008 QST has generated a lot of interest and discussion on the AM Forum (http://amfone.net/Amforum/index.php?topic=17364.0), so I'm writing to get some clarification.
 
I'm thinking of trying a vertical, and I'd certainly rather have four radials than sixty. Please provide some guidance by answering these questions:
 

• What is the definition of an "elevated" radial? Although you made it clear that your advice to use four radials with a vertical mounted on a garage roof applies only to elevated radials that aren't in contact with the ground, I'm curious where the "dividing line" is: how high must the radials be before they're considered to be "elevated"? Is the number a constant, or does it vary with the local ground conductivity?
  
  "Elevated" means insulated and not "on" the ground. A few feet will likely be fine. I have 2 on my 80 meter ground plane and they probably average 4 feet up. I just ran my model changing the radial height from 6 to 3 feet and it made less than half a dB diff. Higher conductivity ground works better than lower, no matter which kind of radial you use and I don't think there's much difference with elevated. With buried or on-ground radials, you will need many more radials with poor ground than with high conductivity ground for the same performance.
  
  BTW, they don't need to be symetrical. I have only two radials in a wide V shape toward Europe. The pattern will favor the direction with radials, but just a bit. Mine has a F/B ratio of about 2 dB.
  
  
  
• Assuming that I can't use "elevated" radials, does it matter if I lay radial wires on the ground, or bury them?
  
  No, as long as the lawnmower doesn't get them
  
  
• What are the tradeoffs when I don't have 1/2 wavelength radials? My lot is only 90 feet wide and I'm going to be hard pressed to fit 1/2 wavelength radials for 80 meters.
  
  With elevated radials they really want to be exactly 1/4 wave long -- as if half a dipole. They can be bent or go toward the property corners.
  
  
• If I can't fit 1/2 wavelength radials, can I compensate by using a greater number of shorter ones?
  
  Yes, for buried or on-ground radials, within limits. Up to 6 or 12 short buried radials, may work as well as 2 or 3 longer, but you will never get to the same efficiency as a large number of 1/4 wave radials with any reasonable quantity of short ones, unless you have highly conductive ground. Buried or on-ground radials are not of critical length, and while 1/4 wave is the norm 3/8 or1/2 wave is even better for buried radials. A salt marsh is the best!
  
  No, for elevated.
  
  
• What can I do to increase the bandwidth of the antenna? I can only raise about fifty feet of vertical wire, so I'll have to match it, but I'd rather not use a complicated remote tuner or have to visit the antenna to change frequencies. Other than constructing a three-foot diameter "cage", is there a third option for a coax-fed vertical?
  
  Yes, a skeleton cage works well. Mine is just 2 wires about 3 feet apart at the top (PVC pipe spreader). It made a big diff in bandwidth, needed to be 6 feet shorter and improved gain by 2 dB. On 80/75, with decent coax the loss, (even with a 4:1 SWR) should not be much. I have 100 feet of LMR-400 for mine, and don't worry about it.
  
  BTW, if you can get the halyards running right, you could have a bent section on top, as in inverted-L, if you felt you had to be resonant. BTW2 at 50 feet, it should also work well on 60, 40 and 30 meters, and shouldn't take a very complicated switchable loading arrangement.
  
  
• If you have your choise of a fifty-foot high vertical or a dipole at fifty feet, which would you recommend for 3.9 MHz, all other things being equal?
  
  Both (I should be a politician ). Actually, I have both -- and they both work well. The center-fed dipole (with window line and a tuner) works great on all bands, but is down just a bit for long haul on 75/80.
  
  My new ground plane hasn't had a lot of use yet, but holds its own against the dipole for long-haul US, but works better than the dipole off the ends, as you'd expect. For Europe, I see about 6 dB increase in sigs on the ground plane -- and get correspondingly more answers. In almost all cases, the noise level on the vertical is higher, so I use the horizontal for receive if I can hear the sig there. Next I need to make a low noise receive loop.

Thank you for your help.
 
73,
 
Bill Horne, W1AC
Life Member, ARRL