To Ground Plane, or not to Ground Plane? That is the question...

[Henry HPSD]

hello henry , welcome to the forum .

im just a cber , not a ham but ive become fascinated about antennas . i understand that having the feed point of a verticle antenna at ground level requires many many many ground elements . i think most of us cb'ers have our antennas feed point about 1/2 a WL (18 feet) or more above the ground . i understand higher is better , but usually money or location keeps a good deal of us from going higher . its seems the main thing is to get the feed point above any nearby structures roofs and we can usually do fairly well . in the cb antenna section were pretty much always talking about elevated base antennas or mobile antennas .

anyhow , what are your thoughts on ground elements on elevated antennas with the feed point 20 or 30 or 40 feet above the ground , on 27 MHz. ?

Hello Booty Monster,

Attached you can find a exel file with calculations made by eznec+ with 4/8/16 radials
(also a couple 100 radials) with antennas at different heigths (3/10/30/60 feet).

Now dont take the gain numbers as a straigth figure wich is appliable to all locations.
It is not. Ground influence will change the gain numbers.
When you live in a desert the difference will be larger.
When you live in real wet grounds the difference will be smaller.

What it comes down to is...
There is difference..but not as much as we hoped. for example a the difference between a 5/8wave with 4x 1/8 wavelength long radials or a 5/8wave with 32x 1/4 wavelength long radials is about : 0,16dB in gain... when the antenna is placed only 3 feet of the ground.

Some say a halve wave vertical needs radials (as a-99) some say not.
The reason for this has nothing to do with what kind of coil there is attached.
It has to do wheter there is a high current or not.
Now adding 3 radials wont do much (not noticable) to a antron 99...when attached many radials you could lift the gain by less then >0,5 dB..now is this worth the effort....no i guess not..

On the otherhand the Imax could get some improvement with adding radials (as you can see in the excel sheet). (there is almost no difference between a normal 5/8 vertical or a .64 length vertical.)
The first few radials are important after that you need many many and long to provide a difference.

The most important thing is i guess where you are located...
In a swamp...the amount of radials become less significant..your sorted out just fine !
In the desert...please do add them as long as possible.

So is it worth the effort...when you place the antenna above ground i guess not..
The amount of mechanical problems etc for just a dB is to much.
co-phasing a couple verticals would do more..

The first few radials are important and speaking about extra gain when going from 1/8 wavelength to for example 1/4 wavelength is perhaps a bit too much in my opionion for the average cb user when it less than 0,5 dB
after the first few radials (4-10) you need to add a lot of radials to make a difference.

Any other point of view is ofcourse highly appriciated !

73 Henry

 

[will85w4]

So should I buy the freaking GPK or not?

 

[BOOTY MONSTER]

thanks henery . i dont have excell so i cant access your attachment . im about the redo the ground plane of my home brewed 5/8 wgp . i went out yesterday and got my materials and most of the hardware . im just gonna do four 90 degree 1/4 plus %5 wl ground elements . i wanted to do eight of them , but id have to use smaller elements with a lot more droop since im on a budget . i know it wouldnt have made any humanly detectable difference , but i wanted an antenna with something different from what everyone else had without adversely affect its performance . so the bigger/stiffer/stronger elements won in the end . ill be using 3/8 inch solid aluminum rods . the antenna will be isolated from earth ground and the mast with a 5 1/16 inch diameter coax choke at the feed point using 10 even wraps of 8x coax . the feed point will be about 30 feet off the ground . i currently only talk on the cb band .

 

[BOOTY MONSTER]

So should I buy the freaking GPK or not?

spend $20-45 more bucks more than the $40 GPK and get a whole properly designed antenna . you shouldnt have any problem selling the imax to get back the additional cost or more .

W-58 Omni-Directional Antenna - Palco Electronics $60 + s&h

Maco V/58 Omni-Directional - Palco Electronics $85 + s&h

 

[dudmuck]

So should I buy the freaking GPK or not?

Depends if you have interference problems with close-in neighbors. Are you causing TVI? or are you picking up noise from neighbors? If so then you need the ugly balun and mast isolation first, taller tower for antenna, then you can think about ground plane for counterpoise. Although, sometimes noise sources are stronger and further away from you and such measure dont help.

that being said, booty is right about the better antennas w-58 or maco v/58.

 

[jazzsinger]

TIP OF THE WEEK,


folding them up to where they add constructively to the vertical pattern in a favourable way is like buying better tyres and negates the need for an extensive radial system when the antenna is not mounted high above ground,

i think what bob is subtely trying to say in his own inimitable style is BUY A SIGMA 4

 

[Shockwave]

I too am unable to see the Exel sheet unfortunately. One thing I am curious about is if your calculations for the Imax 2000 took into account the fact it's matching network is unlike any other 5/8 wave? As you may know the 1/2 wave end fed can work well with no radials but the normal 5/8 wave will have serious issues with both impedance and radiation efficiency without it's radials.

The Imax has an added series capacitor in line with the radiator element. This must have been done to cancel out inductive reactance in combination with the transformer turns ratio to make the Imax perform without a radial system. None of the other "real" 5/8 wave antennas use this type of matching network.

I suggest that this makes a difference in how the Imax would distribute any current into a radial system. I also suspect it is the reason their "gimmick" ground plane kit is not at the correct 90 degree angle to provide a 50 ohm impedance like a normal 5/8 wave. If space permits, I'd sell the Imax and buy a true 5/8 wave groundplane.... unless you can keep a Vector 4000 together at your location.

 

[Marconi]

For those that can't see Henry's last excel file results: there are some formatting problems with word wrap in the header, but I think you can figure it out.

View attachment Antenna Modeling results for 5_8 wave with radials 060410.pdf

 

[Klondike Mike]

So should I buy the freaking GPK or not?

Well put!

 

[Marconi]

So should I buy the freaking GPK or not?

Well put!

For Will, Klondike, and others who are not sure about how useful the GPK works when attached to the Imax/A99. IMO, Shockwave gives the best simple answer below.

The problem with these fiberglass antennas and the groundplane kits is that you simply can't have it both ways. The matching section in the Imax has been specifically designed to work without a groundplane kit. This means it is set up to minimize the current that would be in the groundplane kit so it can function without it.

Now if you look at a "real" 5/8 wave antenna like a Maco V58, it is very dependant on the four radials in terms of impedance and radiation pattern. Take the radials off that antenna and it will very noticeably stop working effectively. Take the radial kit off the Antron or Imax and you'll need microscope to spot the difference because there will be almost no current flowing in the radials.

If you don't believe this, that's fine. You'll just have to try the GPK on these two yourself to really tell.

Are there other considerations or modifications that can be used to make radials effective on the Imax/A99, maybe!

 

[BOOTY MONSTER]

The half wave end fed is one example that doesn't require any ground radials. They work better on a 2 meter hand held then the longer 5/8 wave since you wouldn't use radials there. To my understanding this has to do with the way the matching transformer is wound. The primary and secondary sides are closed coils. It will show a short at DC on it's input and is responsible for providing the 50 ohm match to the coax without requiring something else to "push" against.

The 5/8 wave Imax 2000 also uses a matching transformer. They have some other compensation going on to make the 5/8 wave work without the ground radials because many 5/8 waves with radials use a similar type of shunt fed matching transformer. It probably has to do with the capacitively coupled radiating element on the Imax combined with the transformer turns ratio used to match this antenna.

What's important to remember is the Imax 2000 has been designed to work without radials. Some have even isolated them from the mast and used coax chokes that would eliminate anything else to "push" against and they claim they work well. The groundplane kit is not even close to resonate on 27 Mhz. It may help a little with RFI by decoupling the coax and reducing any residual common mode current on the coax .

If you're going to buy an Imax and a groundplane kit, do yourself a favor and skip both to purchase the Maco V58. It will outperform any of the fiberglass antennas in both signal and RFI reduction. The only time I consider the Imax is when it's installed in a tall tree and then the radials usually have to go. The Vector 4000 is actually the strongest omni with respect to signal however, it's also the weakest mechanically.

"What's important to remember is the Imax 2000 has been designed to work without radials."

should we keep in mind one of Docs favorite lines ? most everything works , but some things work better than others .
the ringo was a popular cb antenna that didnt use ground radials , its no longer sold as a cb antenna , but i think they still sell a 10 meter and other ham versions . it is a aluminum vertical with a tuning ring that looks similar to what the maco uses . wolf radio also did something similar to it .
Wolf Radio.com CB, Ham, Pirate Radio Antennas [CB Antenna]
wolf did use ground elements on its larger .64 antenna though .
Wolf Radio.com CB, Ham, Pirate Radio Antennas [CB Antenna]
so there are examples of other respected vertical antennas on the cb band that didnt use ground elements .

i didnt mean to ignore you post about this earlier . most everything that ive read discussed the need for ground elements on verticals on the cb band and that using the mast or coax for a ground element is asking for bleeding problems . when i tried my home brew 5/8 without ground elements it was definately not tx'ing and rx'ing as well as it did with them by a large ammount . but its similar to the maco and doesnt have the tweeks that you mentioned that the imax has .

The groundplane kit for the Imax also deserves some examination. Normally the 5/8 wave groundplane would require radials at a 90 degree angle to match a 50 ohm feedline. The kit uses radials that are about half the optimum length and sweeps them downward closer to 45 degrees. This is all done to minimize the effect of the radials.

Put some real 1/4 wave ground radials out at 90 degrees on an Imax and you'll probably find it negatively impacts the antennas impedance and VSWR. The internal matching network has already compensated for the absence of radials. Adding effective radials could throw the impedance off when combined with that internal compensation.

when i was considering a 2000 , putting the four 9 foot elements on it was suggested to me by some folks ive come to trust here . some had done some testing or observed positive differences doing that with the antron . so im guessing ............. as with most things antenna wise that location and structures/terrain will have a large effect on how adding ground elements to a 2000 or 99 affect its signal ?

 

[Henry HPSD]

Hello All !

Always good to have a discussion going on !

About:

"the imax is designed to work without radials"...

I have a different point of view:
It is of no intrest what matching device you come up with the current at the bottum remains the same.
Now we can see the imax is closed circuit to the earth and will use the mast and coax as its "counterpoise".

One could see it otherwise...If it really was happing that you could make a matching unit wich would "forgive" the lack of radials.... why isnt it used by broadcasting/military etc?
There would be no need for radials anymore. What can be used for counterpoise on a near 3/4 wave also goes for 1/4 wave

There for i think the first radials do help on the imax as it has a current belly at the bottum.
wich is different compared to a halve wave.

Guess it is important what your expetation is, if your looking for S-units thats not going to be the case.

The "word" in the antenna world is that with eleveted radials 4 is sufficient.

And yes the impedance variees with the amount of radials but this could also be said when speaking of changing height.. u see my point.

For me aswell... if i am wrong please do explain as were all here to learn i recon.

Kind regards !

Henry

 

[Marconi]

BM, basically what Shockwave is saying is the Imax/A99 are a different kettle of fish when it comes to radials. There may be others that are similar, but these two are unique. The 1/2 wave is unique relative to the 1/4 wave and the 5/8 wave, radials will not respond the same in each case. Remember the discussions with Bob85 and his experiences with his Vector 4000, yet another entirely different situation concerning radials. So there is no simple answer regarding the use of radials.

Do you wonder how or why the Ringo and the A99 are said to work fine without radials and your 5/8 wave and my Marconi 1/4 wave will not work so good without radials?

They are each different.

The Ringo and the Maco V58 are similar except for the radials on the Maco. I'm curious as to why the simple Ringo is not made or used much any more, do you know why?

You show images of the Ringo and the Wolf antennas. I have a Wolf 50_11m. It has design flaws and in addition it changes match whenever I raise or lower the antenna just a couple of feet. At best it operates with the best tune showing <>1.7:1 SWR. That does depend on height a bit, with being lower to Earth showing a better match, but all of this would really rankle most CB'rs today.

Maybe this is why these two are not so popular anymore---if they ever were. To be honest, I think both the Ringo and the Wolf are best used close to the Earth, and since they both are 10/11 meter antennas, experience tells us that low heights are no-way-no.

So, if you are interested in the effects of radials on your 5/8 wave, why are we discussing 1/2 wave antennas.

They are each different.

Again, it is just like Shockwave says, "...you can't have it both ways." The term "radials" is truly a generic term, but when it comes to understanding how they work on a particular wavelength radiator, you must consider that each of these radiators are unique with different magnitudes of current flowing in the typical areas around where the radials are attached. Radials are generally located in high current areas like in the 1/4 wave radiator, or with modest current flowing areas as in the 5/8 wave radiator a bit high of the base, or in areas with very little current flow as in the end fed 1/2 wave radiator.

These are differences that must be considered.

 

[BOOTY MONSTER]

i think..............the reason the 11 meter CB ringo isnt made any more is because the FCC doesnt want aluminium cb base antennas sold because they think cbers cant put them up without hitting power lines and cushcraft doesnt want to rile them up .

i just try to understand things and when i dont understand or something is different from what ive read (and hopefully comprehended) im not afraid to ask questions . i am selective about who and what i consider good sources of information because not everythin or everybody is correct . i know sometimes you guys have to dummy stuff down for me (and im gratefull for that) but ill never know why if i dont ask why .

i was of the impression that all antennas needed a ground plane of some sort to work against . if half wave antennas don need a ground plane or ground elements it seems they would be great for mobile use , even though it would need more coil length to shorten for acceptable height . some folks go to great length running ground straps to bond their vehicles to get their antenna to tune .

im here to learn , if ive gotten something bassawkards then id like to be corrected and told what is really going on .

 

[Marconi]

One could see it otherwise...If it really was happing that you could make a matching unit wich would "forgive" the lack of radials.... why isnt it used by broadcasting/military etc?

Among the obvious answers would be for broadcast/military to avoid compromised efficiency and effectiveness in that service situation. They have their own safety concerns, but it is not the same as dealing with the mass public.

IMO, Solarcon's idea was likely trying to fill a niche in the CB antenna market that was created by a Government safety mandate. They probably decided to use the natural occurrence of common mode current flows, rather than avoiding them at all costs. They produced an antenna that did not need radials---further reducing a danger in handling during installations by the public. We know this deal by the Government happened, because at some point in the past things changed concerning the marketing of all metal antennas and for a while the metal type of CB antenna all but disappeared from the market. Solarcon started selling antennas into a nearly monopolistic market for vertical CB antennas.

I have a different point of view:
It is of no intrest what matching device you come up with the current at the bottum remains the same.
Now we can see the imax is closed circuit to the earth and will use the mast and coax as its "counterpoise".

I can't argue the validity of you statement above, but under ordinary conditions we may not choose the Imax/A99 matching device as the most efficient regarding antenna performance, albeit a world of satisfied customers seem to prove different when in use.

The "word" in the antenna world is that with eleveted radials 4 is sufficient.

And yes the impedance variees with the amount of radials but this could also be said when speaking of changing height.. u see my point.

For me aswell... if i am wrong please do explain as were all here to learn i recon.

The veracity of the "word" in the CB or Ham world of antennas is more often than not suspect in my book.

Concering your words on impedance varying. When I'm able to measure such variations on increasing the height or adding radials, I see impedence decreasing. I'm talking about these effects on 1/4 radiators however, and not 1/2 wave or longer.

I can't say your wrong Henry, we are talking opinions here and you have presented you ideas. The other day when you posted the chart for the ARRL, I figured someone may take issue with that presentation claiming at least the chart was directed toward ground mounted antennas. That would have been because the chart talked about radial counts of 16 - 120 which is impossible for elevated antennas. There is also a small print disclaimer regarding the facts presented in the data---as only applying to the references in the body of the text. I'm not sure what your opinion of this chart is, but IMO it is at least representative of the likely trends when adding radials. Long before I ever saw this chart, I noticed some remarkable Field Strength improvements when adding from 3 - 6 radials to a makeshift antenna similar to a Starduster, I call my Marconi 6x. This past year I attempted to repeat this comparison work with a new design, but was unsuccessful in that effort. The problem was not the lack of being able to duplicate the work, I just stopped the process due to some personal problems I was having. I think I have posted the story some where else on this forum. I still want to do that work so that I'm really convinced that adding radials to a 1/4 wave radiator really is benificial.

Hang loose,