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Question about a GPK on an A99

Marconi

Marconi

Honorary Member Silent Key
Oct 23, 2005
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What does adding this kit to an A99 really do for the antenna. It is advertised to lower the TO angle. Some say it increases the range. Some say it improves the ears and call it an ears kit. Some say it lowers the SWR and increases the power output and call it a power kit. Some say it helps with DX and other say if helps improve local and call it a DX kit or a local kit. Some say it does nothing and call it a waste of money and effort.

There are two different A99's. One has no installation bracket and the kit is a hub and 4 elements. The hub slips on the metal base of the antenna and goes up to the top near the adjustment rings. The newer A99 has a mounting bracket like the Imax and the GPK attaches on the bottom u-bolts on this bracket. It ends up near the bottom just above the feed point. This is a different from the older model. Does this make any difference in the way it acts?

What do you think?
 

So the expert asks ? (-: ......I've been through a few antron 99s in my time and i never noticed any differance with the ground plane kit other then it made it easier for it to get caught in the wind and help it hit the ground a little quicker )-: .....Oh I've heard the stories though , better receive , better SWR ??? Huh !! I never saw one that was less then 1.2 around the 11 meter band out of the box !!! (as long as the tuning rings were set right from the factory) The other myth was the GPX's would cause TVI to shower downwards , or then the guys that would put them upside down so they would shoot upwards instead of downwards claiming it helped there TVI problems .......I personally associate A99s with TVI from the time they come out of there boxes , it's just part of the program )-: but !! I will never denie that the Antron 99 transmits and receives with the best of them !! I really don't know if there is such a thing ? but I also conceder them to be "LOUD" sounding antennas as well ......maybe they have the label of being bleed sticks for a reason ? THEY GET OUT !!
 
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forum.worldwidedx.com/viewtopic.php?p=49030&highlight=#49030

posted by freecell

"Another look at the Imax:"

every antenna is a dipole, if it isn't it doesn't radiate, not very efficiently anyway. balanced currents in both "poles" and elimination of common mode current on the feedline and the support structure is a must in any properly designed antenna system. while i don't voice it as often as i once did, low feedpoint heights, feedline and support structure radiation are the main culprits in most tvi and interference situations. in the case of my own antenna systems i make extensive use of baluns, radials and antenna tuners, even with such antennas as the "glass sticks" like the A99 and others and i really don't worry about rf earth-ground returns for antennas that are properly balanced and decoupled. come to think of it, swr is usually the last thing i worry about after poles, (two halves of the antenna) feedline and support current measurements and making sure that the transmitter is always looking into what it takes to keep it happy.

it's not too difficult to understand why most operators fail to realize any benefit from elevated radial systems (or add-on radial kits) when you stop for a moment and ask yourself if there is any antenna current present in the radial system to begin with. if the current has disappeared into the feed and support then what's left for the radials? unfortunately in the majority of cases, there's a lot more involved to proper antenna design and installation than just throwing up the latest entry on the market, adjusting for min. swr and flipping the switch and you and others here know that.

there are two things that can be done to insure the presence of current-as-charge in the added radial system for it to function properly. installing a current choke or a 1:1 current balun will create a high impedance reducing or eliminating common-mode currents on the outer shield of the feedline. the second thing that can be done is to insulate the antenna from the mast or support structure.

once these steps are accomplished the charge-as-current has no choice but to fill the radials with charge when they are added. the ultimate goal is to produce half of the total current generated at the feedpoint in the main radiator and to have the other half divided up evenly among the total number of radial elements.

ideally ALL common-mode current must flow in the radial system for it to function properly.
 
well Switch Kit, I agree. I did forget the one about showering however. And Fl native, I guess FC is right, but I think it was easier for Solarcon to leave them f-glass stick alone and not try and improve them by fixing the CMC's problem. Since they work pretty good, who would mind, when all you have to do to stop the CMC from getting back to the shack is to just lay the coax on the ground from the base of the antenna all the way back to where it goes into the shack. No more of those old bad CMC. But even that doesn't stop them from getting on the feed line and mast under the antenna. I guess FC will just have to get us all up to speed as to how to fix that problem once and for all and then, maybe them old sticks will really get up there and do some talking without having an ear full of air noise.

BTW, SK thanks for the plug, but I'm no expert. At best I may be just a keen observer of some things that go on around me with these 11 meter antennas. But watch out, you may find my foot in my mouth also. I heard a guy describe them stick well just the other day, when he called them ol' sparkie.

I still want to know what you think about the difference in location noted by the installation of the GPK on the old and the new A99 with the mounting bracket? That one is a mystery and speaks of BS in effectiveness right off the bat if you look at the differences close.
 
well the slight offset of the new mounts shouldnt make much difference. just shows that to get that groiund plane working properly like freecell said above mast isolation and then a 1:1 choke balun and your all set. then you will be using the groundplane the way it was meant to be.

why didnt they charge a little more and include a isolation mast stub and a good choke balun in the groundplane kit "shrugs" i dont know.

i did order a choke balun yesterday. i am still looking around town for something suitible to use as a isolation stub to get the antenna mount off the metal mast. then i will test this theory and post results.

now freecell says to put the balun right at the feedpoint.
the balun engineers say to put it at 4.3 feet down or 13 feet down they said would actualy be better. freecell said to ask why so i did. there answer was with the balun right at the feedpoint you could still get horzt. rf radiation bake onto the feedline below the balun, and that by lowering it 4.3 feet or multiples of 4.3 or close to that number that would get rid of the hortz and vert CMC.

now they say also if you go that route to leave the balun free hanging no grounding.

there other sugestion was mount the balun at ground level, but then it would require grounding.

they also said either way free hanging or ground level mounting would remove all CMC completely from the feedline and force all current into the vertical radiator and into the ground plane equaly.
 
(BTW, SK thanks for the plug, but I'm no expert. At best I may be just a keen observer of some things that go on around me with these 11 meter antennas. But watch out, you may find my foot in my mouth also. I heard a guy describe them stick well just the other day, when he called them ol' sparkie.)


Yeah ,me neather. Damned experts have a way of taking my joy away )-: It's all good. I can see that much more aspects of all of this is much more important to others then it can be for me but yet I might be able to learn something along the way ? After 20 years of this stuff , I've learned that the technical can sometimes take the "keep it simple stupid" aspect away from me where it has always worked for me more so then not in the past .....like ....If it works ,don't fix it !! I haven't seen the Solorcon 99 lately ? I didn't even know that they put that bracket on them now ? IM assuming it's like the ones on the Imax 2000s? (made by the same folks) .....I suppose those brackets serve a purpose but I personally liked them without them but after experimenting with the GPX's ......I found the stright stick to do the trick by itself.
 
Well I think your right about that bracket. It may be the Imax A99 that has the bracket like the Imax. It just makes installing a bit easier for the user.

What I am talking about here is that with the ones that have these brackets the GPK attached at the bottom near the feed point. And the older A99 without the brackets, they have around hub that slipped up over the metal base and slip up to the top near the tuning rings and this placed the GPK at the top of the tuning section instead of at the bottom. I understand why this is as it is from a physical standpoint, but what does it do for the antenna? If it doesn't make any difference where the ground plane is on them then maybe that is why they don't work for a hoot. That is just my opinion.

I think in all other antennas with GP's the location of the GP elements relative to the feed point is very critical as to function.
 
Some "I wonder"s

If the mounting bracket covers part of the tuning section, does the additional metal affect the tuning of the antenna, maybe another 'ring'', sort of?
(Didn't even know they changed how the thing was mounted. Makes a difference? Beats me.)

Baluns
Baluns are a means of changing from a 'balanced' condition to an 'unbalanced' condition. That's it. They can also be made in such a way as to be an impedance transformer. Also one of those 'one-of-a-kind' functions and shouldn't be considered 'normal' for a balun. Handy, but not necessary, most of the time. Baluns do not necessarily stop feedline radiation, but they can. A balun's affectiveness ~is~ affected by frequency.
If they are recomended to be placed "this distance" from the antenna/feed point, is the unbalanced feedline above that point then used as 'part' of the antenna in some way, for whatever reason? And what happens to that change from unbalanced to balanced condition? Does moving the balun away from the feedpoint mean that the feedline above the balun still radiate, have the unwanted current in it? Is it in affect just changing the thing from 'whatever it was supposed to be' into a vertical dipole (maybe an off center fed one)?
(Not that it means anything, but I just don't like baluns, or how they're used in most cases.)

Groundplanes / elevated radials
If the thing didn't need them before, why do they need them now? And if they make the thing such a better antenna, why doesn't the manufacturor just make a 'new' antenna that includes them? Two products instead of just one, more income, better 'bid-nez'! (If I can think of that, why don't they think of it? Means I'm smarter than them? I doubt it.)

Lots of "I wonders"...
- 'Doc
 
No 'Doc the Imax A99 has the mounting bracket, but it stop just before it gets up to the tuning rings, just like it does on the Imax 2000. Am I not making my description clear?
 
balun is an acronym for BALanced to UNbalanced, which describes certain circuit behavior in a transmission line, source or load. most communications applications deal with two terminal sources, transmission lines, and loads. this includes coaxial cables, open wire lines and systems working aginst earth or a ground plane as the ”second conductor”.

the first thing to realize is that there are two types of baluns: current baluns and voltage baluns.

current baluns allow the output voltage, with respect to “ground” or outside world, to float to any value required to provide equal currents to each feedline conductor. in essence, current baluns are a universal device that could be used to drive either balanced or unbalanced lines equally well. current baluns isolate the device connected at one end from the device connected at the other end, so the balanced terminals can be used to feed unbalanced or balanced loads equally well. they can also be used as broadband phase-invertors, baluns or ununs.

voltage baluns always try to force the output terminals to equal voltages, which means currents can be far from even! a voltage balun almost certainly guarantees some feedline radiation (or reception), because there are very few “perfectly balanced” loads.

current baluns provide better balance, often have lower loss and tolerate load impedance and balance variations much better than voltage baluns.
 
half-wave vertical antennas:

some antennas that are end-fed or asymmetrically fed can generate current on the feedline even though the balun has low SWR. examples would be a “dipole” or vertical, either symmetrically or asymmetrically constructed, where the feed cable leaves the antenna near a high voltage point. this can be because of a small counterpoise, because the coax itself is the counterpoise, or because the feedline is routed along the antenna or the support structure.

examples where this may be necessary are in small dipole antennas such as vertical dipoles when the feedline does not leave the antenna at right angles, shortened or loaded antennas using the coax as a counterpoise, verticals with very small or shortened radial systems, full-size dipoles using the feedline shield as the “other leg” of a dipole, so-called ‘end-fed’ dipoles which use the feedline as the other half of the antenna and even regular dipoles if the feedline parallels the antenna element for any appreciable distance. In all of these cases, a feedline current choke will greatly reduce unwanted or harmful feedline radiation or reception.

what are the benefits of using a feedline current choke? all of the above antenna examples usually have very high common-mode feedline currents which often lead to:

• rfi problems, either with the amateur equipment or consumer devices

• noise picked up by the feedline being conducted to the antenna

• signals picked up by the feedline decreasing the directivity of the antenna system, especially the front-to-back ratio in the case of directional antennas.

while most common advice is to improve the station’s rf ground, the root of the problem is in the poor isolation of the feedline from antenna currents. If you wish to reduce feedline radiation and improve reception, a feedline current choke is required. in these examples, if SWR is already low, adding a feedline current choke at the point where the feedline exits the area of the antenna will substantially reduce unwanted feedline radiation or reception (noise) without the need for improved station grounding.
 
FC I probably read this wrong, but won't the fix you speak of at the end of you piece "substantially reduce unwanted feedline radiation and (improved) reception without the need for improved station grounding"?

I added the word (improve), but i could be wrong.

BTW, you never did get back to me on the question I asked of you about the bzooka balun mentioned in the article I left you about baluns the other day, and the clarification on the stub idea you presented.
 
Just didn't want to leave any possible chance for missunderstanding out there. You know that is how all them CB truths got started.

Will you give me a few words over there on the place where you posted your thing on coax line transformers a while back. I asked my buddy Elwood for an explanitation, but he said he did not have any time plus I didn't need to know all that stuff at my level of understanding, Dangerous!
 

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