Better performance from a imax.

[bob85]

MC, its working great for local ragchew and european dx, my opinion of the i10k has not changed i feel it is the best 5/8 i ever owned but still not sure how it compares to the sigma hybrid over the long haul as i have not heared the usa or anything further since i took the old antenna down, mother nature is still keeping me guessing

 

[Marconi]

KM, the guys bring up some good points, even freecell's issue about TO angle and NVIS operations has merit.

Some general points about the Imax that I have found. The f'glass antennas all seem to be a bit noisy when compared to just about any metal antenna that I have worked. At 10' high you may also find increased noise. Maybe going higher for that reason alone may be something to consider. I do not know what the prime height for this antenna really is and that may vary with location and soil conditions. But, I firmly believe the match is seriously affected by varying the height. At 10' I can get resistance pretty good, but the reactance is higher than I would like. The SWR is not real bad and I can live with that, but it might be important to have a better match. This situation seems to go away when increasing the height and that may also be a plus.

I have mixed feelings about the ground plane kit (GPK) for this one, but I believe the Imax really does need a good method of isolating the coax from the antenna. I'm not sure the GPK from Solarcon will do that however. I don't have a solution either, but I have been reading on this topic and I am posting in my own thread with some info that I find interesting. I think this might be something to consider about your Imax.

 

[Highlander_821]

With regard to Marconi's question of how to isolate feedline from the Imax to reduce or eliminate common mode currents on the feedline, how about a coaxial choke balun?

 

[Master Chief]

I have mixed feelings about the ground plane kit (GPK) for this one, but I believe the Imax really does need a good method of isolating the coax from the antenna.

I think what needs to be made clear is that a "ground plane" and "coax isolation" are two different things!

I would think that the coaxial balun that Highlander mentioned would work to isolate the coax from the antenna, and we do this for beams all the time. But a balun is really a transformer taking a BALanced antenna to an UNbalanced feedline. For that matter, a gamma match is also an unbalanced feedpoint so should we not use it on antennas with gammas? What about end-fed half waves? I don't have the answer.

More info here:
http://www.hamuniverse.com/balun.html

 

[RoadWarrior]

The Imax 2000 should be at least 18ft off the ground.
No less in my opinion. Higher would even be better.
I would play around with height and see what
works best and then leave it there.
As far as the GPK, i personally have not noticed much
of a difference in performance. However i have noticed
just alittle noise reduction.
That's up to you if you want to try the GPK or not.

 

[W5LZ]

There is no ~one~ ideal height above ground. The two things to think about here are the antenna's reactance to the particular ground you happen to have, which is affected by height, and soil conditions, and making the antennas input impedance match the feed line's and transmitter's. The second thing to think about is the 'shape' of the radiation pattern produced by all of the above. [The low SWR means maximum power transfer to the antenna, the radiation pattern determines where the signal goes.] Juggling all the variables 'correctly' means that you will produce a signal that gets to where you want it in the strongest condition possible for the whole mess. When you optomise for one specific condition it means that other 'conditions' will suffer to some extent. Can't have it 'good' everywhere, just not very likely at all. May be just 'perfect' in one place but other places don't even hear you. (So what else is new?)
Unfortunately, there's no simple, fool proof, absolute way of predicting what's required for each individual set of circumstances. Meaning that there's no ~one~ miracle antenna that does it all. Unless you have control over a few things! Like, height above ground, length of the thing, matching network, and the color of your socks (the last one is more important than you'd believe!). GET control of those things and with porper adjustment, you've got as close to the 'perfect' antenna as you'll ever see...
- 'Doc