"No Ground Plane" Antennas

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af5rn

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There are some antennae specifically designed for use without a proper ground plane, such as on boats, campers, or plastic cars. Does anyone know the specific considerations of using such an antenna on an actual proper groundplane? If you mount one on a metal groundplane roof, will it still work safely? Will it work better? Or will it ignore the groundplane altogether and just work the same as it would work without a groundplane?

I have some theoretical ideas of how it would work, but I'd like to get some input from those who have some experience with this, or at least have considered it technically a lot further than I have.

Thanks in advance!
 

Don_Burke

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There are some antennae specifically designed for use without a proper ground plane, such as on boats, campers, or plastic cars. Does anyone know the specific considerations of using such an antenna on an actual proper groundplane? If you mount one on a metal groundplane roof, will it still work safely? Will it work better? Or will it ignore the groundplane altogether and just work the same as it would work without a groundplane?

I have some theoretical ideas of how it would work, but I'd like to get some input from those who have some experience with this, or at least have considered it technically a lot further than I have.

Thanks in advance!
I doubt it would be a problem.

From what I have seen the groundplane makes little difference to an antenna designed to not need one.
 

DPD1

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Overall it will probably work OK, but DC grounded designs like to be kept away from stuff. If you can get it at least a little off the roof, that would be better. Typically it wouldn't make it better, but there's always flukes.


Dave
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Antennas & Accessories for the RF Professional & Radio Hobbyist
 

DPD1

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Honestly, I'm not sure why. But from experience, I've noticed they seem to be affected more easily by nearby objects. Many times I've found DC grounded antennas, compared to antennas with a ground plane in the same location, will often show a bigger problem with poor SWR when objects (especially metallic ones) are nearby.

Dave
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Don_Burke

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af5rn

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I know some NGP antennae are picky about coax length, with the coax being a tuned part of the antenna's design and performance. That made me wonder if, as DPD suggested, any kind of metal ground plane added into the works might negatively affect performance.

Maybe if the antenna were isolated from the sheet metal by a rubber grommet or something that might help? Doesn't seem like the proximity of the ground plane would be a negative factor, but the actual grounding to the ground plane might be? Hmmm...
 

Don_Burke

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af5rn said:
I know some NGP antennae are picky about coax length, with the coax being a tuned part of the antenna's design and performance. That made me wonder if, as DPD suggested, any kind of metal ground plane added into the works might negatively affect performance.
If the feedline is affecting the way the antenna works, there are other problems in play. Such problems are a way of life in somes systems at HF and below. I see no advantages to such things at VHF and above.

Hanging more conductive material on any active element is going to change the way it works.
af5rn said:
Maybe if the antenna were isolated from the sheet metal by a rubber grommet or something that might help? Doesn't seem like the proximity of the ground plane would be a negative factor, but the actual grounding to the ground plane might be? Hmmm...
Now I see the problem. Grounding one element of an antenna is not something one can do at random and expect good results.
 

prcguy

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Most commercially made no ground plane antennas are end fed half wave with a matching circuit to make the high impudence end of the antenna happy feeding 50 ohm coax. Mounting one to a metal roof can detune the antenna but if the tuning is adjusted to compensate, I see little advantage or degradation from the nearby metal ground plane. If the antenna was of poor design and does not completely decouple the coax from the antenna, the roof mounting may improve this.
prcguy
 

kb2vxa

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Dave, I asked why to test your knowledge and you seem confused. As Don said DC ground and ground plane are two separate issues and here's why. DC ground only means that there is DC continuity between the active antenna element(s) and the mounting structure which is referred to as ground. A ground plane is an artificial "ground" for the active element to work against, a counterpoise. It is a set of radial elements that substitute for earth, electrically raising the ground above the ground.

Actually ALL antennas don't like nearby metallic objects, they become part of the antenna system in effect causing pattern distortion and detuning if close enough. If done deliberately they are called parasitic elements which reflect and direct the signal forming a beam as in a Yagi antenna. In fact the longer one behind the driven element is called the reflector and the shorter ones in front are the directors. Now that I've piqued your interest in antenna theory start cracking the books, then you'll KNOW why.
 

DPD1

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I'm not confused about anything Warren... He asked what an antenna that doesn't need a ground plane would do if a ground plane was nearby, and I basically said that in my experience they can often have more of a problem when they're near something, as compared to one that does need one. Everything else you're adding into this is just another example of you trying to sound like you're smarter than everybody else on here, which is pretty much a daily occurrence. I'm just on here to occasionally throw out some practical knowledge of what I've learned doing this stuff thousands of times over years... Emphasis on DOING, not just reading. I'm not on here to endlessly debate the theories from the ARRL antenna handbook, or "test" people. Next time you feel compelled to make another one of your arrogant comments, do me a favor and just make it... Don't hide it in a question.

Dave
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kb2vxa

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Lookee here Dave, instead of jealously attacking me for my knowledge and experience try using some of your own and answer the question fully and accurately like I did. By that I mean as related to antenna theory and not that of tossing insults and derision.

If you think me arrogant for testing you and finding some confusion, relating relevant and clarifying information to help you and others less knowledgeable than we, and suggesting further study to increase their knowledge and expertise I suggest a little deflation of your ego is in order. A wise man no matter how knowledgeable is humble and without insult. A wise user of a forum understands that replies are read publicly and not directed solely at a single individual. That having been said, on to more productive matters.

30/EX
 

SAR923

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Warren, it's a lot more productive to give what you think is the right answer than to make it a "test". None of us are here to be tested by you. It's especially galling to see you do your usual act responding to Dave, who has certainly built and sold more antennas than you have in your lifetime. Treating him like some newbie is disrespectful and what gets people really cranked off at you.
 

fd71022004

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Testing Dave

Warren,

I don't think Dave needs to be tested and really not here.
I think it is rude.
His posts seem always to
be to the point and helpful.

John S
 
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