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For discussion of the Imax 2000 Review

Author Message   Marconi Posted on Monday, January 21, 2002 - 2:15 am:        833, again a very good report with some great photos. I found a difference between my A99 coils and the one you noted in you A99 report. I do not think that you made reference to the number of coils for both inter and outer coils in the A99 report, but you did mention the A99 outer coil while discussing the Imax. I also counted your drawing of the coil section and I belive you have 21 coils in you A99. But, what ever it is, it looks like it may be a little different from mine. My A99 has 9 coils on the inter coil, same as your A99. However, my antennas outer coil has only 19 turns and I believe you note either 20 or 21. I say all this to state that there may be differences in the A99's out there, not sure though. Looks like a fixed gamma device to me. Marconi   Highlander Posted on Monday, January 21, 2002 - 7:57 am:        Thanks for the great review and discussion. I gather from the better construction that the 2000 may be less prone to causing rf to run back down on the outside of the coax braid? I know people that have knocked the 2000 on that basis because it is so similar to the A-99, which always seems to have the common-mode problem.   Tech833 Posted on Monday, January 21, 2002 - 2:10 pm:        Oh, I forgot to include this in my previous response to you, Marconi. I apologize for omitting this answer to your other question- It is not a gamma. A gamma match runs parallel to the radiator. The A99 and Imax 2000 have what is more accurately described as a 'matching transformer'. It is shunt fed, not gamma fed. The outer inductance coil and series capacitance is a series L-C (inductance-capacitance) tuning circuit.   Tech833 Posted on Monday, January 21, 2002 - 2:05 pm:        Marconi: Thank you. Both of the A99's I disassembled had 20 turns on the inductance coil. The series loss was on the order of .34 dB for the entire LC. The Imax's LC loss was measurable, but barely at .105 dB. Insignificant. I try to keep as much measured technical mumbo-jumbo out of the reviews as possible. Most readers would 'tune out' anyway. Highlander: There would be almost no difference in the amount of RF prone to 'running back down the coax braid' between the A99 and the Imax 2000 simply because of design. However, since the soldering in the Imax 2000 was MUCH better than the A99, that would cause the A99 antenna to be prone to microscopic arcing with the amplitude being fed into it, which would likely cause TVI problems. Example: Looking at a spectrum analyzer with an AM signal modulated symmetrically with a sine wave, the A99 radiated signal would have sort of a 'lawn' of small spikes all over the place both above and below the carrier in the nearfield. This same 'lawn' would be reduced in the Imax 2000 (or an A99 that was soldered properly). I did not conduct that test with this particular antenna, but I have done it with others. The results would be the same. The Imax 2000 power handling is still limited by the conductor size, but it should handle more power than the A99 due to the larger feeder coaxial cable used. That is, for the hams who wish to run 1.5 KW PEP, (full legal power) on 10 meters.   Bullseye Posted on Monday, January 21, 2002 - 3:53 pm:        Tech833 Thanks for the in depth review on the I-Max since I have been seriously looking for a base antenna to use for talking locally I think this one is it. The only question I have is how would you go about adding the ground plane kit to this antenna. Thanks again for the giving us all the facts on this and the other equipment you review!!!!!!!   Copperfan Posted on Monday, January 21, 2002 - 7:17 pm:        i hate to ask this but i have a question what about the IMAX-99?? do you think they improved just the mounting system and left the antenna as is such as a Ant99? the claim says "Relative Gain: 1/2db higher than our famous A-99 antenna" Also do you have any thoughts of the Firestik Fireup-99 Ant 99 upgrade??? http://www.firestik.com/Catalog/FS99-W.htm   Tech833 Posted on Monday, January 21, 2002 - 11:34 pm:        Bullseye: Any ground planes will do. However, from the looks of it, the Antron GPK-1 should work with the Imax 2000 as well. I'm not sure how they changed their ground plane kit to be compatible with the new mounting system. Copperfan: I don't know. I have yet to disassemble a new Imax 99. The Firestik 'upgrade' is not scientifically sound, save your money. Adding a coil where a straight piece of wire used to be is not going to 'improve' anything except Firestik's wallet. It's a lot like those cellular 'wonder antennas' which consists of some conductive traces on a sticker. It's pure snake oil. However, remember this is the land of opportunity, and a sucker is born every minute. CBers seem to be easy prey.   Taz Posted on Tuesday, January 22, 2002 - 12:41 am:        if the gpk would work with the imax that would be nice! how much more gain would i get? would it be noticable on the other side?   Warlock Posted on Tuesday, January 22, 2002 - 6:21 am:        I never liked the gpk's from antron, seemed to add nothing but more tvi. The Maco gpk has worked well for me. 833, if you get a chance you should check out the Mastadon 10k (I think it's called) made by a fellow named Jay in the Mojave. It's a mucho upgraded vesion of the Maco 5/8.   Tech833 Posted on Tuesday, January 22, 2002 - 10:39 pm:        Taz: Re-read the article's closing statements. It very clearly answers your question in real numbers. Warlock: I've seen it. I don't like the feed system or the workmanship. A horizontal feed is O.K., but it tends to raise the angle of radiation when used the way Jay does.   Honkytonkman593 Posted on Tuesday, January 22, 2002 - 11:04 pm:        well tech 833 i must say that that was agreat piece you did on the i max. i thought it would be exactly like the antron 99 but i was wrong. needless to say my antron 99 after being in the air 10 years of faithful service finally died after giving it more wattage then i ever have before. so my question is what is the i max 2000 actually rated at rms not peak?? need to handle at least 1500 dead key will it do it or fail like my poor antron 99?? thanks keep up the good work.   Tech833 Posted on Wednesday, January 23, 2002 - 11:39 am:        I would not run 1,500 watts into the Imax 2000. However, if it was the peak power, you would be O.K. for short 'keydowns'. The problem is, the high current node falls right in the middle of the A99 and a little lower than the middle of the Imax 2000. With 1,500 watts, your base current will be around 5 amps (completely within the Imax 2000 conductor's capability) while the current at the low voltage, high current node can reach nearly 50 amps (pushing it). Keeping in mind that RF does not travel through the center of a conductor, but rather over the surface (skin effect), that means the #14 copper wire is going to get REALLY hot and likely separate. In my professional opinion, the Imax 2000 will handle 1,500 watts peak for short periods of time (like during a normal conversation) for the amateur on 10 meters. More power than that is not only illegal, but likely beyond the capabilities of the antenna anyway.   Honkytonkman593 Posted on Wednesday, January 23, 2002 - 10:53 pm:        thank you for the info. i still might get this antenna as a vertical one. is there one that will handle 1500 dead key ( any other antenna for a vertical)? thank you and have a good one.   Taz Posted on Wednesday, January 23, 2002 - 11:34 pm:        I guess i did not explain myself well enough. When i said gain i meant on the other guys meter. suck as s units   Tech833 Posted on Thursday, January 24, 2002 - 12:24 am:        Hman: Try the Maco V-5/8 or the Cushcraft Ringo for power >1,500 watts. Taz: I have no idea. S units are not a calibrated unit of measure. It is subjective.   Honkytonkman593 Posted on Thursday, January 24, 2002 - 10:54 pm:        can the maco 5000 handle the 1500 dead key? or does it have small wiring like the imax? i havent had a aluminum antenna in years so im curious. how about tvi of the maco verses the imax? thanks   Tech833 Posted on Friday, January 25, 2002 - 10:28 am:        The Maco should easily handle the 1,500 watt 'deadkey' (I think you mean carrier power level, correct??). As far as TVI goes, make sure every connection on your antenna is very tight and then it doesn't matter what antenna you use. Assuming all electrical connections are at zero resistance (not even 0.5 ohms is tolerable), then one antenna will not 'have more TVI' than another. It is actually that simple.   Ae548 Posted on Friday, January 25, 2002 - 9:08 pm:        Tech833, I have a Eagle Tomahawk (w/expanded freq mod)hooked up to my I-Max2k. My swr on the low side was 1.2 and just over 1.7 on the high side. I traded out the top section for a steal whip and shortened it till my swr was just under 1.2 across the entire 10-11 meter bands. What did I do to the series L-C circuit by shortening the antenna? Thanx   Honkytonkman593 Posted on Friday, January 25, 2002 - 11:28 pm:        cool thanks tesh833! i know what im gonna get!! hello maco!! matchs my linear ....later   Tech833 Posted on Saturday, January 26, 2002 - 11:55 am:        Ae548: You didn't do anything to the LC, you simply raised the resonant frequency of the radiator. The top section of the Imax 2000 could just as easily have been replaced with a fiberglass mobile whip of the same length since the 96" top section is nothing more than straight wire.   Marconi Posted on Tuesday, January 29, 2002 - 6:51 am:        Paul, you state the following; "Warlock: I've seen it. I don't like the feed system or the workmanship. A horizontal feed is O.K., but it tends to raise the angle of radiation when used the way Jay does." I am curious. Without getting real technical, why do you feel the angle of radiation will be raised in the case, and how did you determine that? If it is raised, what do you think this angle should be and what do you think it is, as a result. What do you see in the workmanship that looks questionable? I questioned the insulator with Jay and he says it is solid stock Delrone and is much stonger than the radiator. He shows some reinforcing sleeves at the joints and I don't see anyone else doing that. What did I miss here? Marconi   Marconi Posted on Friday, February 08, 2002 - 2:04 am:        Hey Tech833, I addressed the post above to Paul. I am not sure if that is your name or not, but the post is for you. Eddie Marconi   Tech833 Posted on Friday, February 08, 2002 - 10:47 am:        Hi Marconi. Actually, I simply haven't been checking the forums very much, I have been busy building 2 broadcast facilities. When I do get a chance to log in, I just hit the 'last day' link, and I apparently missed your post by more than a day, I apologize. The 'Jay' built antenna had 2 weak points in my opinion: 1). The mounting structure was not strong enough to handle the windload of the antenna structure above it. Although the antenna elements themselves may have been strong enough for 100+ MPH winds, the mounting scheme was not. 2). The cable attachment is at a weird angle and would easily be damaged if a large bird (or flying debris) were to contact it. Antennas like the A99 and such have the coax connect at a point right near, and parallel to, the mast so some tape or a clamp can easily secure it and support the weight of it. It also stays out of harm's way and the copper conductors can't be fractured by wind flex or vibration over time. I suppose if your antenna was mounted low in a residential area, you wouldn't care. However, for my application at altitude in a remote area, it is of major concern. As far as the horizontal feed, I have done a lot of experiments on VHF (BCB) antennas for low power translators and boosters and have discovered that a feed similar to the one Jay uses will cause more ground refraction than a vertical or circular feed scheme. In other words, if you were to 'see' the radiation coming off of the antenna from the side, the pattern would look even more like a 'heart' and less like an oval than a similar element with a more efficient feed system. For stacked (also called 'phased' or 'collinear') radiating elements, this is no longer true, however for a single element radiator like this one, it is detrimental to ground wave performance. The higher you go in frequency, the less this matters. Either way, the 'Ringo' design is that way for a reason. Way before the Ringo, there was a ground plane antenna that used a horizontal feed that paralleled one of the 3 ground planes. On the test range, the takeoff angle was about 3 degrees higher than a 'Ringo' type feed on the same dipole. Best feed I have found so far for a 1/2 wave or similar single element is a 'J' type. However, since the 'J' on 27 MHz. would be over 9 feet long, it is impractical. Your antenna would be over 27 feet long! That introduces all sorts of mechanical limitations, not to mention shipping limitations for commercial suppliers. A good compromise is a 'Gamma' match. You can use a Gamma match on a ground plane antenna too, not just center fed dipoles. Since the Gamma is parallel to the radiating element, the takeoff angle is not usually effected by its presence in the electrical field. Class dismissed for now. I will be addressing this in some upcoming antenna related articles I am writing for Copper. Stay tuned.....   Marconi Posted on Thursday, February 14, 2002 - 1:04 am:        It is hard to argue with a good common sense approach. I will consider your points. Later, Eddie Marconi   Taz Posted on Sunday, April 07, 2002 - 4:03 am:        Mr. Tech 833 I found a guy saying some strange things about the imax 2000 saying it is really a 5/8ths wave. Here is what he said. Here are the measurements that are in every technichan, general, and extra class handbook. 1/4:234 divided by the antennas operating frequency. 1/2:468 divided by the antennas operating frequency. 5/8:585 divided by the antennas operating frequency. These measurements are for wire antennas. For 1in. tubing the measurements get alittle shorter. Its only in every amatuer handbook made. And even on the antenna elmer website where you build your own antennas it tells you that 5/8 is the higest you can get to achieve the best gain. After that the gain starts to drop and the angle of your radiation begins to rise. Now why would an antenna designer tell you that? Hmmmm. Maybe its because he knows what he's talking about. And also why would Solarcon purposely put an incorrect wavelenth on their best antenna? Maybe you should call their antenna designers and fill them in on your suprising discovery. I'm sure they know way more than you and would be intrested on how you came up with such a theory. And why is it that there is not one antenna brand that makes a full wave vertical antenna for 10 meters and lower? Solarcon, Shakespeare, Maco, and Cushcraft all use 5/8 antennas because they know that a full wave antenna does NOT have as good of gain or radiation pattern as a 5/8 antenna in the hf bands. Now when you get into vhf, uhf, and shf a full wave antenna is a different story entirely. The Imax IS 23ft. 6in. but it resonates at five eighths not .64. The measurements your using I've never heard of. The measurements that I gave you are the standard for homebrew wire or aluminum tube antenna. The measurements change depending on what type and size of material you use. The Imax as you know has three sections and is not cut from a single piece of anything. The antenna is made longer to make it tunable over a wider band of frequencys than just one band and this is the reason you use tuning rings instead of clipping the end of the antenna. This also goes for the A99 which can be tuned from 17 to 10 meters and its half wave. The correct electrical length of a half wave vertical ground plain would be 17.2inches and the actual size of the A99 antenna is 18ft. So even though the Imax's measurements show it has a longer length than a 5/8 wave antenna it resonates and I repeat resonates at 5/8 wave. Thats just the way they designed it and thats why they advertise it as being 5/8 wave. Now I'm not trying to fuel the fire. I'm just trying to point out that the Imax is a 5/8 wave antenna despite its length. And why full wave antennas are not used in the hf bands except for short dx. I mean come on, they have mobile antennas that are 5/8 wave and not 23.5ft tall. In this day and age of technology these measurements can not completely determine the correct wavelength of a manufactered antenna. Unless you know exactly how they designed it. All the measurements are good for is designing your own homebrew antenna. And I too run an Imax 2000. Best vertical antenna I've ever used. Basically I want to know if the statements he is saying is correct. Taz   Possum Posted on Thursday, April 18, 2002 - 7:52 am:        I use an antron a99 with maco gpk and the fire up 99 from firestick. tried with and without gpk, i did pick a transmit increase of 2 S units according to my friends base about 25 miles away but I lost that on recieve on my end but a preamp fixed that. With the gpk I found if you bent the radials so that they are straight out and not down I definitely get better skip. I like the fireup 99 tip but to each his own. Possum   Canal_digger Junior Member Username: Canal_digger Post Number: 38 Registered: 1-2008 Posted on Friday, September 12, 2008 - 2:23 pm:        I also wondered if (supposing the Imax 30 degree bend was better than the factory GPK bend) if bending straight out completely like GP ants like Maco, Sirio, Sigma, etc . would make even more of a difference, especially with DX. I'm assuming it would.   Walterb Junior Member Username: Walterb Post Number: 35 Registered: 12-2007 Posted on Sunday, November 20, 2011 - 12:58 pm:        In 2010 I tested (2) A99 an (1) I-MAX 2000 at my QTH in Az an to my amazement both the A99 did better on transmit an receive than the I-MAX 2000 to a mobile 25 miles away using a Wilson 5000 antenna. Using a Cobra 2000 GTL Base radio with A99 with 100' RG8 coax at 36' to the bottom an a !-max 2000 at 24' to the bottom with 100' of RG8 coax there was 36' between the 2 antennas in test an at 25 miles on the Galaxy 98VHP meter in the mobile I read S-5 from the Base Station (100 watts) using the I-MAX 2000 on AM an read S-7 using the A99 same reading were recorded at the Base Station from the mobile. both radios were checked on a B&K 2040 Signal Generator an found to have an S-9 signal input with a 30 micro-volt signal applied! The tips of both antennas were very close to being the same height..........Oldtimer