For discussion of the Imax 2000 Ground Plane Kit Review

Author Message   Tech671 Posted on Thursday, June 06, 2002 - 6:10 am:        I'd love to see a test with the Maco aluminum gpk that mounts perpindicular to the antenna.   Tech833 Posted on Friday, June 07, 2002 - 11:00 am:        I'm not sure the difference would be noticeable.   Alsworld Posted on Friday, June 07, 2002 - 9:46 am:        Okay, dumb question time but I have to ask. I currently run an IMAX 2000, no GPK. Bottom of the antenna (feedpoint I assume) sits 39 ft above ground attached to antenna poles snaked up through, and securely attached to a very tall pine tree. Base of the antenna is about 3 feet below the very top of the tree. I have been fighting the TVI battle and have had much success with grounds, new doubleshielded coax, etc. With this setup, in order to install a GPK I would have to raise the antenna even higher to accommodate the 45 degree sloping of the GPK radials. At a minimum this would put the antenna height even higher to maybe 44 (or +) ft. (and go beyond the fcc height rules). At this heighth, would the GPK further reduce what TVI I have yet to kill?, or being I am so high up already, not make that much difference (with reference only to TVI). Moving my antenna is easy enough and even lowering it (say 1 wavelength of 36 ft above ground)to accommodate the GPK is quite possible, but I would only do this is it is felt that I would really notice reduced TVI. My TVI is one channel in my house that dual low-pass filters and installed high pass filters have not cured. I have an amplified TV antenna in my attic. Yes this is obviously a tough TVI problem to overcome but it's a wonderful challenge so I leave it there. For what it's worth, I have completely overcome any and all TVI problems running barefoot with the above setup. I only affect one channel in my own house while running additional power. I should be content but dig the challenge. My initial thought is the GPK probably would not cure this problem, but if I were to move the antenna where the GPK could be installed, say around a 39 ft feedpoint above ground, could it help?   Tech833 Posted on Saturday, June 08, 2002 - 11:12 am:        Alsworld, Obviously, violating FCC rules relating to power output is not something I can condone. With that said, if the equipment experiencing interference is within a 45 degree slope of the base of your antenna, the GPK would indeed help your TVI problem. If not within the 45 degree slope, then the difference may not be noticeable. Best regards, Tech 833   Biged Posted on Thursday, June 13, 2002 - 5:24 pm:        Alsworld, If you were to go above the hight limit that the FCC says you can put your antenna to overcome TVI on your neighbors tv or phone, wouldn't this be a good thing?   Taz Posted on Thursday, June 13, 2002 - 5:31 pm:        I must ask, where did you put that at? on top of what building?   Tech833 Posted on Friday, June 14, 2002 - 2:55 am:        Biged, You can petition the FCC for a waiver of the height rule if you can prove that additional height is necessary to prevent interference to neighbors' equipment. It has successfully been done many times. The FCC will grant waivers if you can show good cause as to why you need the additional height. Taz, My office is on the third floor. I am currently using the Imax 2000 for receiving LW since I was told to keep it. My attention has now turned to a durability test of the Imax in this installation. It has already survived 40+ MPH winds on that tower. It sure didn't look very pretty though.   Taz Posted on Friday, June 14, 2002 - 6:53 pm:        i know i own one and they sway!!!!!!!!!   Alsworld Posted on Saturday, June 15, 2002 - 5:32 pm:        Taz, Yep, they sure do sway alot. Much more than my 1/2 wave vertical I keep as a spare. I live within spitting distance of the intra-coastal waterway here in north west Florida. I'll bring it down if a hurricane starts coming this way though. Never know if I may need it after the storm for legitimate communication. Biged & Tech883, petitioning the FCC is interesting news but with my setup, I probably won't. I don't bleed anywhere barefoot, even with my amplified TV antenna. Only when running power. With the "box" and an export radio, I think the FCC would definitely frown......then confiscate. My biggest concern was with neighbors. I have worked very hard to clean up any splatter on their electronics and I belive I've found success. I think I might try the GPK in the future once I move the antenna, but for now, neighbors are happy and so am I. Funny thing, never bothered my satelite dish no matter how close they were together. Thanks for your excellent reviews Tech883! Alan   Tech833 Posted on Sunday, June 16, 2002 - 1:35 pm:        It's a shame that your station has to be run that way. I'm glad you have the problem settled for now. I hate hearing stories of people having to 'do without' simply because of close proximity low-quality electronics. The fact is, the FCC set power limits on CB stations for a reason. That is one reason as to why they are set low. If you are licensed in a service which allows more power on lowband, then it is assumed that operators have some technical ability to make their stations' emissions clean enough as to not cause interference. I have seen very few CB stations and accessories which are not likely to cause interference. It's not an 'add-on' that is needed to clean up CB gear, but rather a complete re-design of the entire transmitter. In order to keep costs down on CB radios, the transmitter sections lack adequate filtering. If a manufacturer did design a 'cleaner' and properly filtered transmitter section, the cost of the radio would skyrocket! Example: Motorola LMR mobile radios with fewer 'channels' and MUCH fewer features that your average CB radio cost $1000 and more. Why? Because the FCC designated much higher standards for equipment used in part 90 radio services. Of course, to date, Motorola radios meeting or exceeding the technical requirements for part 90 services have never been cited as the cause of unintentional interference. Some of the SW and BC transmitters I maintain have outputs of over 100 KW (100,000 watts). I can sit right in front of a 100 KW transmitter with the antenna less that 25 feet away and watch TV with no signs of interference at all (even while transmitting on frequencies close to CB!) Why? The transmitters are designed from the ground up with the intention of the cleanest possible output. Broadcast transmitters are built to specifications much tighter than those for CB gear, ham gear, and almost all professional radio services. It's not a 'fliter' that cleans it up. The transmitter design itself is much more complicated and cleaner than a CB radio. So, it CAN be done..... For a price.   Marconi Posted on Friday, August 02, 2002 - 9:49 pm:        I recently read a post somewhere about how close does a ground plane have to be, relative to the feed point, in order to provide the proper GP resonse. You make a comment in your report on the Imax 2000 GPK as follows: "The Imax 2000 is a .64 wave antenna which theory tells us highly benefits from a counterpoise beneath the feedpoint and radiating element." I believe experience tells me that a GP needs to be pretty close to the feed point and/or radiator in order to have the proper affects. I also believe the GP needs to be at or below the feed point, and certainly should be below the radiator, with a preference of being below both, as your comment implies. Question! I believe the Imax GPK, in your report, is located above the feed point by several inches. In the case of the A99, the kit is usually installed even further above the feed point. In the case of the A99 the kit is usually up near the top of the base mount in order to be out of the way. How does these installations stack up against your comment about the theory? I have attempted to measure some response differences comparing the A99 with and without the GPK, and I have never noted anything but a mild leveling (broadening) of the SWR curve under one scenario or the other. Since I saw no dramatic real world differences I assumed the A99 GPK was non-responsive because it was located in the wrong place, well above the feed point. I do not question your results. This is just what I have observed. Marconi   Tech833 Posted on Saturday, August 03, 2002 - 1:03 am:        The feedpoint of the A99 and Imax 2000 is actually just above the top of the aluminum sleeve where it meets the fiberglass. The aluminum mounting sleeve just contains a coax jumper that goes between the SO-239 connector at the bottom of the antenna and the actual feedpoint (see the photos). In the antenna reviews, I took pictures of the insides alongside the outer shell in the correct proportion so you can easily see where the actual feedpoint is. Concerning your first question, yes- you are correct. In order for the ground plane to be a ground plane and not look like a capacitor at the end of a string, the ground needs to located as close to the feedpoint as possible.   Marconi Posted on Saturday, August 03, 2002 - 8:54 am:        I see your point about the actual location of the feed point. Consider the following. Assume that both the Maco V-5/8 and the A99 w/o GPK are end feed 1/2 wave radiators and that both would naturally present a rather high impedance match at the feed point without any matching device. The Maco's matcher would transform to 50 ohms with the GP included and the A99 does not need the GP. I will make another assumption here. I believe that the presence of the Maco's GP should itself lower the impedance somewhat just by being there. So the Maco's matcher does not have to make as much of a transformation as the matcher in the A99. If the A99 matcher tunes the antenna to 50 ohms, how could the presence of a GPK improve anything? Marconi   Marconi Posted on Saturday, August 03, 2002 - 9:24 am:        Another point about location of the GPK on both the A99 and the Imax. In the case of the A99 the typical location of a GPK will be very close to the feed point as it should be. The Imax, on-the-othe-hand, seems to be somewhere around 10" below the feed point. When we discussed close earlier, is this close enough to be effective? Why then, does the Imax place the GPK attachment bracket near the bottom of the mounting bracket instead of higher up on the bracket? Am I being too pickey? Marconi   Tech833 Posted on Saturday, August 03, 2002 - 12:04 pm:        Lots of questions... First off, the Maco 5/8 and the A99 are NOT both 1/2 wave radiators. The A99 radiating element measures somewhere near 830 ohms and almost 450 ohms inductive. The 5/8 would be less resistive AND less reactive than the A99's 1/2 wave element. Therefore, the A99 would have to have a different matching network altogether. Since the Maco element has much less reactance and slightly lower resistance, the matching network would be inherently less lossy. Also, add the fact that the Maco matching network is a large diameter aluminum tubing section. That raises the Q of the network considerably over the A99's #16 wire network. Next, the Maco's GP's will lower the feedpoint reactance much more than the resistance. You left half the equation out here. Yes, the resistance would go down too, but the reactance number changes by a vector of nearly twice again. Next, although the A99 network does transform the feedpoint to 50 ohms j0, you have only half-way designed the antenna. I can get a ball of wire to match, but what about the radiation pattern? The GPK lowers the takeoff angle of the field. Now, since the A99 is a 1/2 wave antenna, you could do the exact same thing by mounting it on a metal roof or even by using a pole and metal guy wires. In the case of the Imax 2000, the GPK makes a LOT more difference since it is a .64 (let's just say 5/8) wave antenna. The presence of ground is almost essential to getting any kind of performance out of a 5/8 wave design. A 1/2 wave is not as critical to ground capacitance. Lastly, 10" is nothing when you are talking about a frequency whose wavelength is nearly 37 feet. 10" translates into a vector impedance of a little less than 0.2 ohms.   Marconi Posted on Tuesday, August 06, 2002 - 8:25 am:        You are probably correct about the Maco not being a 1/2 wave antenna. However some will argue that point as it does seem a bit short. This is why the first word I used in my consideration was "Assume...." I was just curious as to how adding a GPK to an A99 could make any improvement if the antenna was already matching out as well as you suggest. Usually adding additional radiating material into the RF field near the feed point causes some reaction to tune. I saw no response to the tune in my experiment with this one either, but I was thinking, that is strange, the GP must not be close enough to have an effect. You are no doubt correct. Generally, I considered the angle of departure was mostly effected by the height and the length of the radiator only, meaning longer and higher was probably better. Good discussion! Thanks Marconi   Ss8541 Posted on Wednesday, August 14, 2002 - 8:26 pm:        i just found this topic...nice write up 833. did you sweep the antenna with a tdr or a tracking gen with return loss bridge to confirm the bandwidth of the antenna? just curious, as this is something that i had planned to do in the future. if you have already done that, then i see no point.   Tech833 Posted on Wednesday, August 14, 2002 - 11:03 pm:        I used an Eagle return loss bridge and the tracking generator function in my IFR 1200 Super S service monitor to do the sweep. Later, I used the same return loss bridge on the IFR 1500 too (different day in testing). I used a Potomac OIB-3 to measure the feedpoint R and j.   Ss8541 Posted on Wednesday, August 14, 2002 - 11:48 pm:        the ifr's are nice comm analyzers. i'm ordering a -loaded- motorola 2600c(h.stab ocxo, trk gen, high performance specan w/markers, etc) this week(tomorrow actually). i can't wait for it to get here. the monitor comes with a cable fault tester, but the eagle rlb150n3d is the bridge i am looking at purchasing, to make this a better setup. i want to do some testing of antennas, filters, preamps, etc in a similiar manner to what you did here. i just need the time and the web space to do that. anyway, i asked this question because i didn't see anything on bandwidth in your post. but i could have missed it if it was there. anyway, did your bandwidth match the advertised bandwidth? if you stated this, and i missed that, sorry.   Tech833 Posted on Thursday, August 15, 2002 - 5:16 pm:        I was able to determine that the return loss was better than -10 dBm over at least 1.8 MHz. I have the RLB 150 N3B. It is a nice addition to the IFR and stores in the lid nicely. My 1200 Super S has everything in it. The add-ons seemed like a good idea when I bought it, but it sure drains the internal batteries quickly when I need to operate away from A/C or D/C (like in the middle of a field). The TCXO eats the most juice. I sometimes whish I could switch the heater off.   Ss8541 Posted on Friday, August 16, 2002 - 11:41 pm:        -10db return loss(a 1.9:1swr for those who do not speak return loss) for a 1.8mhz spread. so i guess their bandwidth was 'fudged' also (3mhz at 2:1 swr). but it still looks like a good antenna to me. i would like to see you do the same with the shakespear version if you have the time. and i ordered the 2600 yesterday. its like xmas in august. and i should feel that way seeing that this is almost as much as a small car(and this is for a 1998 used version). the battery option was the only thing i didn't go for, since 'field work' for me is always at a tower site. i haven't been to a tower site yet that didn't have ac power(if power -was- down, that was 1st priority).   Tech833 Posted on Saturday, August 17, 2002 - 11:57 am:        A lot of my work is done in the field, and there are times when I have to go out to variuos points along the antenna array for something (like when I am working on a curtain). My battery gets used a lot. I also use it when I am headed to a site for some emergency work (off the air). I turn the IFR on when I'm about 3 minutes from the site so that the TCXO is warmed up, on frequency, and ready to go when I arrive. My 1200 Super S is a $25K unit. Even with the hefty price tag, it paid for itself in a year. IFR says they are discontinuing the 1200 series in favor of the 120B. They told me they will give me $2000 trade in value on my 1200 SS for a 120B. No thanks. That 2600 is a really nice unit. I hope you enjoy it for a long time. I hear from fellow engineer's who own them that they take a beating and last forever! Copper did send me a pre-damaged (in prior shipping) Shakespeare antenna to check out. Unfortunately, it was missing the internal tuning section components. If you like, I could share the internal elements configurations at least. BTW, it is a 3/8 wave antenna over a 1/4 wave sleeve. Shakespeare's engineer has been convinced for many years that the 3/8 wave antenna is the way to go. I admit, the field patterns and bandwidth are impressive.   Hoopguitar Posted on Sunday, August 18, 2002 - 9:42 am:        T-833, Please give us the info on the Shakespeare. Thanks, Hoopguitar   Swamper Posted on Monday, September 30, 2002 - 12:10 am:        id like to read a review on the army big stick also..thanks!   Mikefromms Intermediate Member Username: Mikefromms Post Number: 143 Registered: 6-2003 Posted on Thursday, April 15, 2004 - 1:47 pm:        I hear the big stick has now been discontinued. I guess Imax 2000 put them out of business. mikefromms   Phoenix New member Username: Phoenix Post Number: 5 Registered: 2-2003 Posted on Wednesday, April 28, 2004 - 6:29 am:        I heard that too, which bites....I wanted one...!   Capt_hook Intermediate Member Username: Capt_hook Post Number: 304 Registered: 6-2004 Posted on Monday, February 19, 2007 - 10:39 am:        OK ! so with all these test in simple laymans terms where is the best place to put the ground plane kit on a IMax 2000 ????for it to work and not just look good .thank you .............Capt Hook   Tech808 Moderator Username: Tech808 Post Number: 13048 Registered: 8-2002 Posted on Monday, February 19, 2007 - 11:49 am:        Capt_hook, Just follow the mounting instructions's as the Imax GP kit bracket bolt's right to the mounting plate of the Imax. Lon ~ Tech808 ~ N9CEF CEF#808 ~ CEF HAM#33 ~ CVC#002 10-10 #61493 ~ 10-10 VP#2688 Tech808@copperelectronics.com   Capt_hook Intermediate Member Username: Capt_hook Post Number: 305 Registered: 6-2004 Posted on Monday, February 19, 2007 - 12:29 pm:        Ok that was easy...........and simple ....Thank you lon .........Ron   Muddoc New member Username: Muddoc Post Number: 7 Registered: 1-2010 Posted on Thursday, February 18, 2010 - 11:32 am:        TVI - add lowpass filter / good ground's (pine tree)