Basic ground plane antenna questions

[montyhouse]

Been considering building my first basic ground plane antenna. I had two basic questions (and, yes, I'm "Elmer-less").

In the example below from the ARRL, the radial is doubled up. I'm assuming that the desired radial length (for your chosen frequency) is not affected by twists, bends, etc., but thought I'd first ask.

Second question is: Do I end up with an omnidirectional, unity gain antenna?

 

[AK9R]

I think what they are showing is take a length of copper wire that is twice the desired radial length, bend it in half, pass it through one hole of the SO-239, solder it, then reshape the radials so they are 90 degrees from each other.

Here's a potentially useful video on building one of these antennas. About 6 minutes into the video, you can see what he's trying to accomplish. The ground plane elements of your antenna should be arranged in a similar fashion.

 

[WA8ZTZ]

Second question is: Do I end up with an omnidirectional, unity gain antenna?

Pattern will be pretty much omnidirectional if feedline is matched to the antenna.
The basic ground plane you are building really has no real gain.

 

[tommytimbertoes]

You don't have to double it like that, one wire is enough. It's omni.

 

[KC5AKB]

You will find some folks use bolts and nuts for the ground radials.

 

[anneranch]

Make sure you are discussing / talking about "ground plane antenna" - most people will assume "vertical with ground MOUNTED radials".
These are electrically different.
Construction details / methods vary - electrically you are still having an antenna with 1/4 wave vertical active radiator and with one or more 1/4 wave long , active "horizontally sloped , above ground radial(s) ".

PS Specifying "antenna gain " without mentioning directivity is nonsense. As already pointed out - omnidirectional antenna has no gain.

 

[paulears]

Just remember that ¼ wave verticals are a design that requires a ground plane - as in a very large conductive surface - naturally, that would be the sea. The ¼ wave is tuned to length with maths. Unless you live on a boat - you won't have a ground plane as good as the sea, but multiple bits of wire a ¼ wave long behave similarly to the sea - 4 is usually considered the norm, but three can work too. More than 4 and your surface area electrically behaves more and more like the sea. The other type of ¼ wave has one going up, and another straight down - this then becomes a half wave dipole, with broadly the same performance as the ¼ wave ground plane. the directional pattern, viewed from above is the same for both. A circle where all compass directions get favoured the same. Some ¼ waves use ground plane elements bent downwards - this changes the horizontal radiation a bit, which might send more horizontally and not so much up at 40 degrees or so. Depending on where your 'other end' is, this can help or hinder.

 

[anneranch]

PLEASE read my last post.

Ground plane antenna IS NOT same as "vertical" ...

There is NO "the other end " on "groud plane antenna " ...
Even "large conductive surface " "required" for "vertical" is boggus / incorrect.

I am positive that your vertical antenna setup is working well for you,
but propagating these misconceptions is not cool.

Let sea be, we are trying to discuss antennas.
Cheers

 

[sonm10]

Actually, you're the one who's wrong. An antenna needs to be a half-wave or a full wave to work. (Please don't ask all the how, I don't understand myself all the physics). A 1/4 wave antenna REQUIRES a groundplane that reflects one half of the half wave. Similarly, a 5/8 wave antenna REQUIRES an inducting coil to match to 1/2 wave. 7/8 wave antennas also have coils to match for a full wave.

So, if you really wanted to get technical, a "vertical" needs to be EXACTLY 1/2 or a FULL wave to work WITHOUT a groundplane.

PLEASE read my last post.

Ground plane antenna IS NOT same as "vertical" ...

There is NO "the other end " on "groud plane antenna " ...
Even "large conductive surface " "required" for "vertical" is boggus / incorrect.

I am positive that your vertical antenna setup is working well for you,
but propagating these misconceptions is not cool.

Let sea be, we are trying to discuss antennas.
Cheers

 

[paulears]

I’ve no idea why she’s got. A bee in her bonnet. The topic is basic ground plane antenna. It would be hard to find a ground plane design that doesn’t feature vertical elements wouldn’t it? What misconceptions are being propagated? I thought that a little expansion of the design he’s following would be helpful. He asked sensible questions that were generated by the advice to fold the radials back, making it possible that the radial design was the key feature in these antennas. The centre fed dipole, mounted vertically shares a huge amount of the physics, and the performance. I simply am a bit surprised by your indignant response? The subject of antennas is much more complex than needed for this query. Why complicate it?

 

[RadioDXfun]

Just to add, you should never assume a 1/4 wave ground plane antenna is ground mounted with radials. They can of course be elevated successfully.. would you put a 1/4 wave GPA on the ground for VHF at home ?

A ground plane antenna can be a vertical 1/4 wave radiating element and a ground pin. It will be very inefficient. So add the radials to improve efficiency.. 4 minimum ideally, the more you put down (or up if elevated) to about 60 will give you a max of about 2.4dB less losses over none, that is worthwhile.

A 5/8 wave is actually electrically extended to be a 3/4 wave using the coil which also serves to match the impedance. (sometimes with a capacitor) but a coil alone works. I know as I have built and used them myself and get SWR of 1.2:1 with just a coil and extensive radials.

The way I see it is if the radiating element is vertical the antenna is known as a vertical. Radials or counterpoise are not even strictly necessary for a 1/4 wave. However without them performance will dive.

My own view on 1/4 waves, they do work but I have no idea why anyone would ground mount them if you have alternatives. You get -6.0dBi gain at 5 degrees using MMANA-GAL. Much of F2 layer ionospheric propagated RF comes in at very low angles on 10m. This can VERY easily be improved on by a great margin by elevating a 1/2 wave end fed for example. At higher frequencies the gain from elevating is an astonishing improvement at low angles.

A 1/4 wave ground mounted will work DX but is very easily outclassed for DX (especially on 10m band) a basic Sirio GPS27 1/2 wave correctly set up and elevated 7m - 10m AGL will totally destroy a 1/4 ground mount on 10m for a lot of the very low angle DX. This will be most apparent when the conditions are weak, I will go as far as to say given low noise RX QTH it could make or break an F2 layer DX contact in marginal conditions).

GPE 5/8 GPS 1/2

GPE 5/8: 5/8 λ ground plane GPS 1/2: 1/2 λ, Omnidirectional, 26.4 ... 29.0 MHz Tunable, Systems: 10m-HAM

www.sirioantenne.it

Also a 5/8 wave is omnidirectional and it does potentially have gain. Not much, but 1- 2 dB or so in some situations is a real possibility, the main lobe is focused down a bit giving a little lower take off on the main lobe and a little extra gain from the far field ground reflection which has a constructive phase interaction at reasonably low angles.

 

[anneranch]

If it is posted on internet , IT MUST BE TRUE...

READ AND hopefully learn something ...or not

Antenna Ground Plane: Theory & Design » Electronics Notes

Using an antenna ground plane can enable a simulated ground to be made and allow the antenna to be mounted above ground

www.electronics-notes.com

 

[RadioDXfun]

Hi Anne, what is it you are trying to prove or disprove exactly ?

The irony being of course you just linked up to something posted on the internet.

A ground plane antenna can be ground mounted or elevated. To quote from your link:

" As the name indicates the antenna ground plane acts as a simulated ground. "

That simulated ground can be on the ground or elevated. (as opposed to the earth/soil or which is not simulated, as it is actually the ground)
or dirt as Americans call it.

 

[anneranch]

Hi Anne, what is it you are trying to prove or disprove exactly ?

The irony being of course you just linked up to something posted on the internet.

A ground plane antenna can be ground mounted or elevated. To quote from your link:

THAT is incorrect - the ground plane antenna radials are purposely SLOPED ( to control the feed point impedance )
hence it is ILLOGICAL to mount them physically on the ground .



" As the name indicates the antenna ground plane acts as a simulated ground. "

THAT is also incorrect - there is nothing being simulated.
You do not say "one side of dipole is active and the other simulates ground".



That simulated ground can be on the ground or elevated. (as opposed to the earth/soil or which is not simulated, as it is actually the ground)
or dirt as Americans call it.

As plainly visible in this thread - I cannot convince the group that "ground plane " and "vertical antenna" are NOT SAME in theory of operation.
So in desperation I posted the link .

I am not that foolish to prove anything to an audience which is not interested (in antenna theory) ...
I am still waiting for somebody to chime in with " I worked DXCC in 15 minutes with my vertical... "

Since you are an exception , and apparently read the article - - please note that "ground plane (antenna) " consists of MINIMUM of two 1/4 wavelength elements , where "vertical (antanna) " dimensions ARE not LIMITED to 1/4 wavelength.

 

[RadioDXfun]

I understand "a vertical" in casual conversation to mean pretty much any vertically polarized antenna. I agree it is not interchangeable
with 1/4 wave ground plane antenna as a specific design. One is a general term to describe a subset of antennas based on their polarization and a 1/4 wave ground plane antenna has/is a technical design. (albeit flexible, ground mount/elevated, 1 radial, 4 radials, no radials with ground pin)

But I cannot see where anyone mixed it up.

 

[anneranch]

I understand "a vertical" in casual conversation to mean pretty much any vertically polarized antenna. I agree it is not interchangeable
with 1/4 wave ground plane antenna as a specific design. One is a general term to describe a subset of antennas based on their polarization and a 1/4 wave ground plane antenna has/is a technical design. (albeit flexible, ground mount/elevated, 1 radial, 4 radials, no radials with ground pin)

But I cannot see where anyone mixed it up.

The original poster stated "my first basic ground plane antenna." Nothing casual about it , very precise .
Majority of the group participants went off the subject , rather typical of many discussions.
That is OK , more power to them, but it is irresponsible to keep spreading
these false , baseless "hearsay opinions" , especially to newcomers.

 

[RadioDXfun]

I will make this my last post on this topic.

The original poster uses GPA terminology when making a GPA. I cannot see any problem with that at all.