Gain I-max 2000

[erik_ark]

Woohoo my first post on this forum :shock:
Here is my question / problem:

I was looking at several site's (American and Dutch) for prices of I-max 2000.
But now I saw that on most American the site's ( http://www.bellscb.com/products/antennas/solarcon/solarcon_IMAX2000.htm & http://www.thomas-distributing.com/ant-solarcon-base1.htm ) that the antenna has 5.1 dBi gain and on Dutch site's such as www.dile.nl and www.scanman.nl that it has 10.9 dBi gain.
How is it possible that there is a large difference between the Dutch and American site's?
And what implies gain exact? Can someone give me clarity?

(Sorry for my bad English )

Greetz Erik

 

[bob85]

welcome to the forum eric, i think the reason theres a big discrepancy in the gain figures is because the 10.9dbi figure is make believe, the 5.1dbi figure is much nearer the truth but still optimistic for that particular antenna imo, no regular vertical antenna is anywhere near 10.9dbi gain unless its a collinear antenna and that would be one giant antenna on 27mhz, even a 3 ellement beam has only around 7 or 8dbi gain but claims of big gain figures sells antennas, if one manufacturer claims something then the others must feel like they need to do the same or lose sales, they dont say what direction or angle this gain is in compared to an isotropic radiator but its certainly nothing near 10.9 dbi useable gain, the american solarcon sites and the itallian sirio website seem to have cut back on the stupid gain claims for their cb antennas, i have often wondered why when the manufacturers no longer claim this does the advertising and literature that comes with the ones sold here in the uk still have the silly gain claims, maybe somebody more clued up than me can give us their thoughts on this.

 

[W5LZ]

Erik,
The amount of gain that an antenna has depends on what it is compared to. When gain is expressed in "dBi", it is a comparison between the antenna in question and an 'isotropic' antenna (an imaginary - 'perfect' antenna). If the gain is expressed in "dBd', then it is being compared to a dipole antenna (real antenna positioned in the same place as the antenna in question).
Then there is the fact that most CB antenna manufacturors try to express 'gain' in the largest possible number (no idea if the Dutch do the same, but suspect that they do, a little bit)!
You also need to know that the isotropic gain figures are a bit misleading if you don't remember that a dipole antenna has a positive gain figure of something close to 3 dBi, which would bring that 5 dBi gain figure down to something like 2dBi, when all is said and done. (5/8 th wave antennas do have slightly more gain than a 1/2 wave dipole antenna. But not much.) You should also realize that any gain figure, dBi or dBd, is relative to mounting mounting location, near the ground or in free space as the isotropic antennas are. Since the location of an antenna can be different for each and every installation, so can the gain of that particular antenna. It can decrease very easily, seldom ever increases, and is almost always NOT what is claimed by the manufacturor.
If the two antennas you ask about are really the same design, then the gain of each antenna is very close to the other (if not the same). Higher gain figures tend to sell more antennas. I think that gain figures are the product of the advertising depeartment, not necessarily the electronics department, so should be taken with large doses of 'salt'. The gain figure for a typical 5/8 th wave antenna is very near 1.5 or 2 dBd and is roughly comparable to a typical dipole antenna.
Another one of those "ought to remember" things is that a fractional gain figure means that the supossed gain will never be heard by a listener. To actually be heard, the gain figure has to increase by a minimum of about 3 dB. Most fractional gain figures are "rounded" to the next highest whole number, in most cases.
- 'Doc

PS - Can you tell that I believe gain figures are over rated?

 

[Highlander_821]

Bob85 is pretty much on the money. Put more bluntly, antenna ads LIE!!!

Imax2000 is probably 2 or 3 dbi. They are good antennas, though. Maybe a little pricey with oversized shipping and all. But they are simple to assemble and mount, they are quite durable, and they get the job done for those who don't want to go with a beam for whatever reason. They also have a very wide swr curve from 26 to 29.7 MHZ, which is nice.

One other issue--I think a 3 element yagi has about 7dbd (1/2 wave dipole reference), which would put it's dbi at around 9 dbi. Yagis are usually referenced to 1/2 wave dipole for gain figures.

 

[RoadWarrior]

Don't go by gain figures as stated by antenna
ads when looking to buy an antenna.
The Imax 2000 gain is somewhere around 2.9
and 3.2 with the GPK.
A true 1/2 wave antenna will out-perform a 1/4
wave antenna and a true 5/8 wave antenna will
do better than a true 1/2 wave antenna.
The actual total radiating element length of
the Imax 2000 is 270.5 inches which makes it
a .64 wave antenna. Slightly, larger than 5/8 wave.
But, my I-10K 5/8 wave out-performs my Imax 2000.
So, the larger antennas doing better isn't 100% true.

 

[erik_ark]

OK. Thank you all for the quick answers I asked the same question on Dutch forums 6 days ago, and I haven't got any replys there.

 

[erik_ark]

I have found this (http://www.video-observer.com/imax/imax2000.htm) article about the I-max 2000.
They say the antenna has 2.9 dBi gain. Is that is near reality?

 

[Highlander_821]

Yes.

 

[erik_ark]

Yes.

Thank you