Benefit of Ground Plane Kit for A99

[Brain the Dog]

I'm almost ready to install my new A99. Even thought the A99 is not the best performer, I like it because of its proven physical durability. I've had one on the house for 25 years with no issues from hurricanes and winters.

I now also have a new GPK with my A99. The new A99 will be attached to a metal pole that is cemented into ground and is also grounded by 2 or 3 8-foot ground rods. Between antenna and radio, there will be a poly phaser (3 foot RG 213 jumper coax from antenna to poly phaser, 25 foot RG 213 Coax from Poly Phaser to radio).

Top of antenna will be 47-feet from the ground. Before I install the GPK, I want to know... will there be a decent benefit for the transmit and receive of the antenna with the GPK? I'm worried a bit about the added wind-load that will be caused by adding the GPK. If there is no benefit to transmit and receive, I might not install the GPK.

The GPK has been advertised for decades to give 30% more gain, to lower angle of radiation, to improve both transmission and reception. But I want to be sure.

So, to finally resolve this perpetual question, I'm posting this thread!

 

[The DB]

No, it doesn't. Contrary to what many people believe, ground planes do not have those affects on an antenna. They don't affect gain or the angle of radiation enough to be noticed, and if you do notice a change from adding one, that is a sign that you had a problem with the antenna before installing it.

That isn't to say that there aren't benefits to using a ground plane kit, said kits are very good at minimizing to eliminating things like common mode currents. They also have a stabilizing effect on the antenna above them, making it so that various changes have less of an affect on the antenna itself. There are other benefits as well, but gain and angle of radiation are not among them unless you have other issues in play that you may or may not know about.


The DB

 

[midnight special]

on a antron99 changing the u bolts or cleaning the spot where the antenna touchs the mast makes a difference,,i dont want to start a argumnet but the mast is part of the 99s system,, i have seen it a lot here in florida,, guy puts up antenna puts on rusty mast and complains about noise cant get out and such,,, but i tell him to clean where the antenna touchs mast and put some new not rusty ubolts and he will usually see a difference,,,,

 

[Brain the Dog]

No, it doesn't. Contrary to what many people believe, ground planes do not have those affects on an antenna. They don't affect gain or the angle of radiation enough to be noticed, and if you do notice a change from adding one, that is a sign that you had a problem with the antenna before installing it.

That isn't to say that there aren't benefits to using a ground plane kit, said kits are very good at minimizing to eliminating things like common mode currents. They also have a stabilizing effect on the antenna above them, making it so that various changes have less of an affect on the antenna itself. There are other benefits as well, but gain and angle of radiation are not among them unless you have other issues in play that you may or may not know about.


The DB

How does common mode currents effect performance of the antenna? What do you mean by "stabilizing effect on the antenna above them"? And what other benefits does the GPK give the A99?

 

[The DB]

How does common mode currents effect performance of the antenna?

Common mode currents can change the antenna's radiation pattern. Enough of them on the wrong length mast/feed line can cause a good part of your signal to move up to a higher lobe, as well as a few other effects mentioned below.

What do you mean by "stabilizing effect on the antenna above them"?

Things that Midnight Special was talking about won't have nearly as much of an effect on an antenna with a ground plane, even the shortened ground plane of the a99's gpk.

And what other benefits does the GPK give the A99?

A lot of people call the a99 a noisy antenna, and a bleed stick. I am not going to say a GPK will fix all sources of noise, and stop all possibility of bleeding in your or your neighbors houses, but it will minimize one possible (and common) source of both, namely CMC's on the feed line/mast.


The DB

 

[Marconi]

Brain here are my models of an A99 with slanted down radials that represents a mast with common mode currents (CMC). The patterns are an overlay of two model that are Isolated from the Earth in order to show the effects that Earth makes.

This is not a complete indication for the reduction of CMC, but it hopefully shows is the difference CMC can cause.

Model that is isolated at the top of the mast by 3" inches. Notice the absence of (red line) currents on the mast.



The antenna pattern.



Model with the mast connected to Earth and not isolated. Notice the more obvious (red line)currents on the mast.



The antenna pattern.



Here is an overlay for both antennas above. The first image is the Primary model in black ink with the cursor on the maximum gain and angle. This model is not isolated.

The second image shows the model and is in blue ink, and the cursor is on the maximum gain and angle for the model that is isolated.

These models are intended to give us an idea for the effects of CMC on this A99 model.



The second image, model that is isolated.

 

[Marconi]

Here is the A99 model that is without radials an is isolated from the mast. If you decide to use this model and setup your A99 without radials, you should also use a coaxial choke at the feed point or something similar that works to stop CMC on the feed line.

A99 with no radials and is not isolated from the mast or the Earth. Notice in this antenna view data at the bottom that the mast is 432" inches 36' feet to the antenna.



Antenna pattern


Model that is isolated from the mast by 3" inches at the top.



The antenna pattern.


Here is an overlay for these two models for comparison. You'll notice there is not much difference, but it is still a good idea to install a air wound choke at the feed point just in case your install has the problem of CMC.



I hope this help demonstrate the possible CMC issues for your new install.

 

[Brain the Dog]

Here is the A99 model that is without radials an is isolated from the mast. If you decide to use this model and setup your A99 without radials, you should also use a coaxial choke at the feed point or something similar that works to stop CMC on the feed line.

A99 with no radials and is not isolated from the mast or the Earth. Notice in this antenna view data at the bottom that the mast is 432" inches 36' feet to the antenna.

View attachment 19262

Antenna pattern

View attachment 19264
Model that is isolated from the mast by 3" inches at the top.

View attachment 19265

The antenna pattern.

View attachment 19266
Here is an overlay for these two models for comparison. You'll notice there is not much difference, but it is still a good idea to install a air wound choke at the feed point just in case your install has the problem of CMC.

View attachment 19267

I hope this help demonstrate the possible CMC issues for your new install.

Thanks, Marconi. I need a bit of help in understanding your pictures. With the GPK.. it looks like the radiation pattern is extended more than w/o the GPK... but I'm not sure if my interpretation is correct.

I"m also a bit confused by "isolated from the earth." I always thought that it was a good thing to have a solid grounding of everything, that the antenna would benefit from being bolted directly to a mast pole that is mounted into the ground and properly grounded.

 

[Marconi]

I need a bit of help in understanding your pictures. With the GPK.. it looks like the radiation pattern is extended more than w/o the GPK... but I'm not sure if my interpretation is correct.

BD, here is the A99 with and without the GPK as an overlay so you can compare the differences. This model shows the A99 produces three lobes at this height above Earth.

Which lobe are you concerned with being extended in the image below?

I"m also a bit confused by "isolated from the earth." I always thought that it was a good thing to have a solid grounding of everything, that the antenna would benefit from being bolted directly to a mast pole that is mounted into the ground and properly grounded.

I mentioned earlier that there are other considerations to be made dealing with CMC. The subject has been broadly discussed right here on the forum. Just do a forum search for common mode currents. Any other questions about the modeling, just let me know.