IMAX 2000 GROUND PLAIN?

[MADMAXS 455]

Any body got any thoughts about a home made ground plain
set of radials for an IMAX.
I talked to someone on the DX side and he said he used some old super scanner elements to acheve this.
So it's got me wonderin what realy works?
We got a 50ft tower it's gonna hang on, just wonderin what can make it better.
PS. and dont sugest another antenna. 8)

 

[Switch Kit]

I never ever saw a differents with a A-99 when ground planes were involved .....waste of money as far as IM concerned ! Kind of reminds me of those little ground planes they sell for Wilson 1000/5000's ......surely a joke !! Imax does not need a ground plane but I certainly don't see why you couldn't experiment on your time and dime. Good Luck

 

[FL Native]

the reason a imax doesnt need a groundplane is becuase it uses the coax as a counterpoise/groundplane. adding the groundplane kit will lower your angle of take off.

just get the kit GPK-1.

 

[MADMAXS 455]

I got an old beat up A99 with the kit.
So there the same are they.
I like the idea of lower angle take off hope-ing that it would help with the local comunications.

 

[W5LZ]

Whtever difference you notice will be slight. It will not make a big difference at all, or if it does, there was some kind of problem other than no groundplane. If that's worth the price of the kit to you, buy it.
- 'Doc

 

[PLUTO]

Several years ago, I bought a groundplane kit for my A99 (around $40 ) It didn't take long to realize it was a waste of money and time.

 

[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.

 

[MADMAXS 455]

Well guys I finally got the nerve up on a still day to do the ol climb up the 50 ft tower and hang that 2000 and so far it's doin the job.
My friend about 30 min says there's an extra 1.5-2 S-units on his little ol' radio and people an hour away (that is if your driving 55mph down the back road) said S2-3, that is with a solid 200 wiskeys goin up there.
And mind you I could never hear those guys an hour away before because there always running bearfoot.
At least now on a quiet night I can hear their modulation.
So far so good.
now I gotta get a beam up there someday.

 

[MADMAXS 455]

Oh and That's with no ground plains.

 

[Marconi]

So 455, are you telling us that the difference in contacts and signals are due to going from the A99 w/o GPK to an Imax w/o GPK?

 

[W5LZ]

...sounds reasonable.
- 'Doc

 

[MADMAXS 455]

Yup yup

 

[Switch Kit]

I knew a guy that used the ground plain kit upside down on his Antron 99 ....he swore up and down that it helped reduce a lot of his TVI .....He always sounding great !! ......I wasn't going to argue with him or doubt his theroy , but boy did that antenna look silly up ther in the sky like that !! ......but I always though those sigma 4s looked kind of strange as well but boy did those antenna's kick some a$$ out there on the airwaves !!

 

[FL Native]

well ... i didnt notice much difference going from a99 to shakespear ABS-2010 to imax2000 ..... and when i got the imax i got the gpkit with it.... until i seperated the mount from the metal push uppole and added a 1:1 feed line choke balun. then i noticed THE difference.

allthough now its 1:1 resonant point is now bellow ch1. its still bellow 1.5 from like 25-28mhz thats with or without amp on little more reflect with amp on but swr the same. 8)

example: 27.475 is 1.5 with amp on and 1.4 with out, and 26.9150 = 1.3 on and 1.2 off. "shrugs"

 

[Marconi]

FL Native, in 1996 I got an old A99 from a buddy that said the antenna was bad. It just had water in the coil section and putty was plugging the drain hole up. Still working fine today. He had a GPK with it also, but he said the same as many others have said, it did not make any difference to him.

Well I wondered about that so I tested it. I too could not really see a big difference, but I did notice one thing. I ran an SWR bandwidth curve on the antenna with and without the GPK. Without the GPK the curve was almost flat from 26.515 to well past 28.000. I did the same test with the kit installed and now the antenna produced a very nice curve from 26.200 to 27.665 that was well below 2.0:1.

However, just like you, I noticed that resonance was down at about 26.800 somewhere, and I thought that strange. With out the kit I could not really tell where the antenna was truly resonant because it looked the same just about everywhere. I did not like that broadband aspect, because it just did not seem natural and I figured that there had to be something making losses in order to produce that characteristic. So I figured the GPK's did have some value, but it was not really enough to really perceive anything in working the radio.

Good observation.