Pros: Good performance, simple assembly, well built.
Cons: Looks flimsy in the wind, fiberglass splinters with age.
The Imax 2000 is marketed as an 11m CB band antenna. However, the extra wide bandwidth of the Imax 2000 also lends itself well to amateur radio bands, and many hams have installed an Imax 2000 to cover some of their favorite HF spectrum.
The Imax 2000 is as simple as it gets as far as assembly. It is only 3 pieces, each threads into the next. The whole antenna can be assembled in under 2 minutes. The mounting bracket is a flat aluminum plate with holes for the 2 U-bolts (included). It will accept masts with diameters up to 1 1/2 inches. The RF connector is a standard SO-259 and accepts the popular PL-259.
The first thing you notice about the Imax 2000 is that it is LONG! After removing the inner conductors from the fiberglass radomes on an experimental Imax, I measured-
Bottom section: 80 inches
Middle section: 94 inches
Top section: 96.5 inches
That makes the total radiating element length 270.5 inches. Using 27 MHz. (CB) as center frequency (which this antenna was designed for), that makes the Imax 2000 a 0.640 wavelength antenna. (A 5/8 wave antenna is 0.625 of one wavelength). I was very surprised to find that the Imax 2000 is not a 5/8 wave as advertised. The Imax 2000 is actually a .64 wave. A .64 wave antenna is the highest gain single element design there is with 0.4 dB more gain on the horizon (free space) than a 5/8 wave element.
Back inside the fiberglass, the Imax 2000 uses RG-213 coaxial cable connecting the SO-239 connector in the bottom of the mounting pipe to the coils of the matching section. The internal soldering is fabulous. This is much better than the Antron 99's RG-58 internal cable. The center section uses capacitive coupling in the radiator similar to the bottom section.
With the radiator length being .64 wave, the impedance at the feedpoint is extremely high. The Imax 2000 uses a matching scheme similar to the Antron 99 with a small coil inside a larger coil and a 4 pF series capacitor. The inner coil provides a 50 ohm tap on the driven element, while the outer coil cancels out the capacitive reactance created by the coupling capacitor and the capacitance at the fed end of the radiator and also allows the outer tuning rings to vary the value of the high-Q outer coil for simple end-user fine tuning. One of the big secrets to getting a wideband antenna, which many other antenna makers apparently ignore, is completely canceling out the reactance, and having the reactance track with frequency. Even a few ohms of reactance at the feedpoint will greatly reduce the bandwidth. By tuning the reactance to zero, and using components that will track with frequency change, the SWR will be very low over a wide frequency range.
The whole reason for going with the capacitive coupled radiator in the first place was to meet the rules for CB antennas being able to insulate up to 14,500 volts. Lots of people were getting injured and killed from installing CB antennas that fell across power lines, so this was an attempt to thwart any more deaths. Of course, not all power lines are below 14,500 volts potential, but a lot of neighborhood lines are. This is one "feature" I am not willing to test!
The Imax 2000 is a very well built and well thought out antenna. It's ironic that the Antron 99 paved the way for this antenna, but the Imax 2000 is head and shoulders above the Antron 99 in engineering practice. So much additional inductance coil is needed in the Antron 99 to get the highly capacitive 1/2 wave element tuned. However, in the Imax 2000, with the .64 wavelength element, the capacitance is much lower, which requires much less inductance to tune it out. Therefore, much less coil is required to tune the Imax 2000 to resonance, which greatly reduces the coil losses.
So what is the TRUE gain of the Imax 2000? Assuming a .64 wave shunt fed dipole in free space, minus the losses associated with the series capacitance and inductance, and minus the necessary counterpoise, according to my math, the Imax 2000 has 2.9 dBi gain. That is to say, the Imax 2000 has 2.9 dB gain on the horizon over an isotropic radiator. Referenced to a center fed 1/2 wave dipole, which is the industry standard, the Imax 2000 has a gain of 0.8 dB. This could also be stated as 0.8 dBd gain. Although adding the Antron GPK ground plane kit will not add much gain to the Antron 99, the ground plane kit would add some gain on the horizon for the Imax 2000. A 0.64 wavelength radiator is much more efficient and will have a much lower angle of radiation (keep the signal down on the horizon instead if wasting it up in the sky) with a proper counterpoise system. Adding the GPK to the Imax 2000 (according to my math and previous .64 wavelength test range plots) will result in a 0.3 dB gain improvement. This will bring the Imax 2000's actual gain up to 3.2 dBi (or 1.1 dBd).
On air, you will find that the Imax 2000 is a good performer both on transmit and receive. It isn't as 'noisy' as some aluminum antennas in wind or dry conditions. The bandwidth allows it to cover the 10m, 12m, 15m, and 17m ham bands under 3:1 SWR. 10 and 12 are under 2:1. Reports on the Imax compared to a horizontal dipole are favorable. In my own tests, 9 out of 10 signals on 10m and 15m are better on the Imax than the tuned horizontal dipole. You can run full legal power into the Imax 2000 without any problems.
Some people have complained about the fiberglass fraying with age and exposure to the outside world. It is very easy to prolong the life of your Imax 2000. Simply wipe the fiberglass down using lacquer thinner on a soft rag. This removes all the surface wax and oils. Then, coat the antenna with some common lacquer spray paint. Don't use a metallic type paint. Clear lacquer is your best bet.
In the wind, the Imax 2000 really whips around! I suggest that if you live in an area that gets winds over 40 MPH, you use some non-metallic rope and guy the antenna somewhere near the middle or upper 2/3. Although most people say a lot of sway is 'normal', it made me pretty nervous. I didn't want the antenna to snap and a piece of it fly through a neighbor's window!
The Imax 2000 easily outperforms the Antron 99 and other 1/2 wave antennas like the popular 'Ringo'. Adding the GPK ground plane kit will provide a some improvement in gain on the horizon, which will noticeably improve local communications. With the wide availability and reasonable price of the Imax 2000, it is easy to suggest this antenna to the 10m ham and 11 meter enthusiast who desires top performance, and a low profile, neighbor friendly fiberglass antenna that is simple to assemble and tune.