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

will85w4

will85w4

Active Member
Apr 12, 2010
152
6
26
Coachella Valley, So Cal
I have the IMAX 2000 base antenna setup in my backyard on top of a 21ft antenna mast. I am curious as to whether or not the GPK that you can buy online is really worth it? I have made successful contacts with the way my radio and antenna is setup, so I don't see the point of fixing something that ain't broke. Would it simply improve current conditions? Any suggestions?

will85w4-albums-cb-stuff-picture1941-a.jpg
 

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quiksilver said:
The general senses is....................No GPK. They really don't help. You could almost buy a Maco V-5/8 for the price of the kit.
JMO
Click to expand...


Says who? From what I read the general consensus is to USE the GPK when possible. I have it on my Imax. It must help. It can't hurt. It's only around $35 bucks now for a lifetime on benefit. Well worth the little money.
 
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.
 
hey shockwave , not arguing , but just trying to understand . its my understanding that all antennas/verticle needs something to work against . optimally a groundplane .

since "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." what does the antenna work against ? does the matching section also minimize currents going into the coax shield and mast ?

its a mixed bag going by forum comments about the effectiveness of adding groundplane kits/elements to the imax ans antron antennas . some say no diffference and some say big difference . i dont recall anyone saying their performance decreased when adding them though .

since a maco cost less than a imax and the maco is a whole antenna it would be the better performer and less money spent .
 
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Everyone in my area that has the Imax 2000 ( and most do ) none use the GPK.

They all get out real well and talk DX with ease.

I just put up my Imax 2000 and I went ahead and installed the GPK.

I figured it couldn't hurt since I was only going to be able to have the feed point around 18'.

The GPK was fairly cheap. If it had of been expensive I would NOT have installed it.
 
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.
 
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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.
 
Shockwave said:
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.
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so do you think full 1/4 WL 90 degree ground elements are better on elevated 5/8 WGP's than full 1/4 WL elements that are sloped at 45-35 degrees ? i understand your post to say thats true on the imax because of its matching network , but on a typical coil or ring tuned 5/8 does it matter IYO ? from what i understand its kinda splitting hairs either way .
 
The angle of the radials determines the impedance on a normal 5/8 wave groundplane. To arrive at 50 ohms they should be at 90 degrees (except on a Imax). The length of the radials contributes to the gain of the antenna. The full 1/4 wave radials will provide more gain then the shorter ones used on the S-827. The difference between 4 and 8 is negligible.
 
Shockwave said:
The angle of the radials determines the impedance on a normal 5/8 wave groundplane. To arrive at 50 ohms they should be at 90 degrees (except on a Imax). The length of the radials contributes to the gain of the antenna. The full 1/4 wave radials will provide more gain then the shorter ones used on the S-827. The difference between 4 and 8 is negligible.
Click to expand...
So more is not better? would it not be in the case of shorter gp radials?
 
Adding more short radials like they do on the S-827 will not compensate for the fact they are half of the optimal length. More radials being better is technically correct. However, with an elevated 5/8 wave groundplane on 27 MHz, you will not see any noticeable increase from 4 to 8 radials. With something like a 1/4 wave vertical on 80 meters, the case is different. Some will use over 100 buried radials.
 

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