NGP antenna with a GP?

[SSTJ]

A theoretical question for our resident antenna experts.

Let's say that I have a dual-band mobile antenna connected to a mag-mount on the hood of my TJ. Now I remove the antenna and replace it with a no-ground-plane antenna. Any consequences?

In other words, will a NGP antenna work any better or worse if it is given a ground plane? (In this case, via the mag-mount and hood.) Or will it ignore the ground-plane?

Here is an example of a NGP antenna.

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@Mr. Bills
@Jerry Bransford
@Zorba

 

[KingCarGuyZ]

If I remember my antenna theory correctly, a no ground plane antenna would ignore a ground plane because it is not in the radiation pattern. so in theory the antenna would be un-effected or potentially slightly improved.

- dont quote me on that tho. Im not an antenna guru.

 

[SSTJ]

If I remember my antenna theory correctly, a no ground plane antenna would ignore a ground plane because it is not in the radiation pattern. so in theory the antenna would be un-effected or potentially slightly improved.

- dont quote me on that tho. Im not an antenna guru.

Ok, interesting.

Well, I've read on two forums today that it would actually compress the radiation pattern a bit into something more horizontal, with less vertical propagation. In some cases I suppose that might actually be a good thing.

 

[SSTJ]

Here is what ChatGPT thinks:

If you were to attach a no-ground plane antenna like the Diamond AZ507RSP to a mag-mount on the hood of a car, the performance of the antenna would likely be compromised. The reason is that no-ground plane antennas are specifically designed to work efficiently without a traditional ground plane or radials. When you introduce a ground plane, such as the metal surface of a car's hood, it can alter the antenna's radiation pattern and impedance characteristics, leading to some potential issues:

1. Pattern Distortion: No-ground plane antennas are designed to radiate effectively without relying on the ground plane. Introducing a ground plane, such as the metal car hood, could disrupt the antenna's intended radiation pattern, potentially leading to less predictable coverage and reduced performance.
2. Impedance Mismatch: No-ground plane antennas are designed with a specific impedance to match the radio's output impedance. When used on a proper mounting surface (without a ground plane), they achieve the desired impedance. However, when mounted on a metal surface like a car hood, the impedance may be mismatched, leading to a less efficient transfer of power between the antenna and the radio.
3. Signal Loss: A mismatched impedance caused by introducing a ground plane can lead to increased SWR (Standing Wave Ratio), resulting in more reflected power and potential signal loss.
4. Interference: The metal car body may act as a reflective surface for radio signals, leading to potential interference and multi-path propagation issues, which can degrade the overall performance of the antenna.

In summary, it's generally not recommended to attach a no-ground plane antenna to a metal surface like a car hood. If you want to use the Diamond AZ507RSP antenna on a vehicle, it is best to mount it on a non-metallic surface, such as a fiberglass or plastic mount, to maintain its intended no-ground plane operation and ensure optimal performance. Always follow the manufacturer's guidelines and recommendations for proper antenna installation to get the best results.

 

[Jerry Bransford]

NGP antennas are nowhere near as good of a performer as those that require a ground plane. There is no reason to use a NGP antenna on a Jeep as there was on my fiberglass boats.

 

[SSTJ]

NGP antennas are nowhere near as good of a performer as those that require a ground plane. There is no reason to use a NGP antenna on a Jeep as there was on my fiberglass boats.

Yes, understood, thanks.

But back to the question, which I admit is more theoretical than practical: would adding a ground-plane to a NGP antenna improve its performance, diminish its performance, or make no difference?

Don't worry, I won't actually do this on my TJ; I just want to understand.

 

[Jerry Bransford]

Yes, understood, thanks.

But back to the question, which I admit is more theoretical than practical: would adding a ground-plane to a NGP antenna improve its performance, diminish its performance, or make no difference?

No, that'll just unbalance it and reduce its performance.

 

[SSTJ]

NGP antennas are nowhere near as good of a performer as those that require a ground plane. There is no reason to use a NGP antenna on a Jeep as there was on my fiberglass boats.

Hi @Jerry Bransford

I know we're getting a bit off topic now, but I have a follow-up question here. Why/how is it that our TJs provide a good ground plane anyway?

Here are some reasons I would think they wouldn't, so could you correct my understanding?

• The shape of a TJ body and/or frame looks nothing like a "plane".
• The shape of a TJ body and/or frame are shaped nothing the radials commonly used in place of a plane.
• Even if the TJ were shaped like a plane or like radials, it's still the case that when mounted over a tail-light, the TJ body and frame are all contained in one quadrant (90 degrees) of the circle surrounding the antenna.

Thanks for any insight.

 

[Jerry Bransford]

When the antenna is properly mounted and it has a good large surface area bare metal connection, not just a ground wire, it actually has a very good ground plane since the entire Jeep including its frame serves as a ground plane. Its body angles etc. don't really affect it enough to worry about. I actually considered installing a tall vertical 'flag pole' HF ham antenna for 10 through 40 meters behind my home but decided against it due to its required ground radials I didn't want to have to dig trenches for.