coily wilson striker stargun predator nugatron solarcon audioking penetrator crossbones slingblade monkey made whiskey still just to name a few........ these antennas all have one thing in common. they are all physically shortened, electrically lengthened quarter wave antennas. they all attempt to match the performance of the full size 102" steel or fiberglas whip. that will never happen, for obvious reasons. this open-air, coil loaded design has been re-invented for decades, using better quality this and stronger that and so on and so forth. the only thing that has really been raised to new standards are the prices, higher and higher with every new attempt. too many newbies to cb radio have been fooled into thinking that the more power an antenna is capable of "handling" the better it is. there is absolutely no truth to this whatsoever. none. sure, if you're planning on running 5 - 25 thousand watts of power they may be the way to go but for the average, everyday user they are simply a waste of time and money. the full size 102" steel or fiberglas whip, when mounted in a center roof location of the typical vehicle yields no more than 0.0dbd of gain, or unity gain when referenced to a half wave dipole. this being the case, the open-air, coil loaded versions of this full size quarter wave antenna will never perform any better, and in all instances will perform more poorly, all other things being equal. while it is true that they may have a slight advantage over the 102" steel by maintaining a more consistent swr due to their ability to remain more rigid while the vehicle is in motion, this is about the most or the best that can be said about them to their benefit. it would seem that the prevailing mentality dictates that the only way to improve transmitted and receive signal strength (mostly transmitted) is to find one of these coil-loaded monsters and buy/use unnecessarily large amplifiers in the never-ending quest to "out-do" the other guy. anyone who operates a tractor-trailer rig will tell you immediately that the most difficult direction in which to talk or hear from is the back of the trailer. a basic, non-technical understanding of the majority of the popular antennas used on tractor rigs will make this relatively simple and easy to understand. all of the antennas listed above have several inefficiencies/shortcomings in common when used in most applications, especially when used in the usual mounting locations offered/available on most 18 wheel tractor rigs on the road today. the first and most notabable of these is the fact that in a coil-loaded design such as these, (or any lump-loaded antenna design) the most electromagnetically active region of the antenna is the bottom or the "base" of the loading coil itself. the problem is that when the shaft underneath the loading coil is so short that the base of the loading coil can't even clear the roof metal in the cab of the tractor, several things can and do occur, none of them beneficial to producing a decent signal, especially with respect to the rear of the rig. the higher up the base of the loading coil is in the air, the further horizon it "sees" in the distance, in all directions. the further horizon it is able to "see" the further it is able to "talk" and "hear." this is why people who are in the business of antenna design realize that in this particular application especially, top-loaded antenna designs are "the way to go!" (see firestik website) since the very definition of antenna gain is the elimination of radiation wasted in unwanted directions and at unwanted angles, (or being impeded/reflected and/or absorbed by large metal masses) it makes all the sense in the world to utilize a top-loaded design in an effort to be able to get as much signal as possible into and out of the antenna/system for more effective long-distance communications. there are even models of top-loaded antennas on the market which utilize multiple loaded quarter wave elements to achieve usable gain when referenced to their single element counter- parts. (including the 102) these multi-element designs used singly or in pairs can provide ground wave coverage approaching distances of 50 miles or more under non-skip daytime conditions with modest equipment and without the use of amplifiers. i have also seen a few capacitively top-loaded (top-hat) antennas that perform exceptionally well. so why was it again that you wanted to re-invent the loaded 1/4 wave? in addition, a number of tractor rigs incorporate stacks on one or both sides of the tractor to the rear of the mirrors which can be utilized as "parasitic elements" creating a directional effect which can be taken advantage of as well. anyone who has tuned an antenna in the proximity of these stacks and has been paying attention soon realizes that the presence of the stack in the near field of mirror-mounted antennas drives the resonant frequency of the antenna higher and thus requires the antenna to be tuned "longer" than normal (in the absence of the stack). this occurs because of the capacitive loading effect the stack imposes on the nearby antenna. since capacitance introduced into an antenna system in this manner has the effect of physically "shortening" the antenna, (or raising the resonant frequency) it must be tuned longer to compensate for the coupling introduced by the stack. once i discovered this my next question was, is the stack longer or shorter than a 1/4 wavelength at 27 mhz.? realizing that if the stack was shorter i could use it as a director element and conversely, if it was longer than a quarter wavelength it could also be pressed into service as a reflector element! it wasn't long before i discovered that the majority of stacks were indeed shorter than a 1/4 wavelength at 27 mhz. with further experimentation i discovered that with a couple of pieces of coaxial cable, a couple of inexpensive relays, a 12 volt source in the cab, some control line and a switch i could introduce "stubs" to lengthen the stacks effectively changing them from director elements into reflector elements, making the system "steerable" between front and rear. i have also seen that some are beginning to incorporate these ideas into passenger vehicles, as is evident to anyone who has done any serious surfing of radio-related websites on the internet. my point in writing this article is simply this. it is indeed admirable to want to EXPERIMENT and try NEW things related to antennas and antenna design. but do you really want to continue doing something that has literally "BEEN DONE TO DEATH" or do you want to try something TRULY NEW and DIFFERENT and really IMPROVE your SYSTEMS PERFORMANCE? _____________________________________________________________________________________________ Who are you going to believe? Making The Case For Dual Antenna Systems. In this corner........ The Ultimate Guide to 11 Meter CB Antennas http://www.signalengineering.com/ultimate/mobile_antennas.html Co-Phasing antennas simply means taking two identical antennas, mounting them on the vehicle and feeding them in-phase. One of the biggest misconception of radio operators is what kind of effect this has on the radiation pattern. Most people think that after you phase two mobile antennas, your signal will be strongest in line with the vehicle body (meaning the signal is strongest down the road straight in front of you and straight behind you also. This is the theoretical effect that you would get from co-phasing two omnidirectional antennas. However, to realize this effect you need to satisfy a couple of requirements. For one, a good earth ground with long (over a wavelength or so) radial wires is required. Secondly, at CB frequencies the closest you would be able to place these antennas are about 18 feet apart. Since it is impossible to satisfy these requirements, the effect of co-phasing is seriously diminished. Unfortunately, even the "Radio Shack Antenna Book" states that co-phasing two mobile antennas will produce a two directional signal. So then, is there any advantage to co-phasing two mobile antennas? Why yes, there is. Before we noted that the radiation pattern of a single antenna is "pulled" where there is the most metal vehicle body. You can see the pattern is not perfectly omnidirectional like we would expect it be. As we travel down the road, you will notice signal fade ("flutter" or "waver") from this uneven radiation pattern. Co-phasing two antennas will even out the pattern irregularities. Instead of making the pattern more two directional, it will make it more omnidirectional. Do not expect more "gain" from two antennas. Figure 3 shows how phased antennas clean up the radiation pattern. Read the section "Phasing" for instructions on how to make a harness to feed your phased antennas. It best to get them as far apart as possible. The best way would be to mount one on the front bumper in the center and one on the back bumper in the center also. Most people think this looks silly (me included!) and mount one on each side of the vehicle. In the opposing corner........ Copyright © 1996 Firestik® Antenna Company http://www.firestik.com/Tech_Docs/SNGL-or-Dual.htm Truck drivers' made phased antenna set-ups popular back in the early 70's. There are several good reasons for their use. First of all, phased antennas create a directional pattern that favors communications in front and in back of the vehicle. This is ideal for truckers and RV's that use their radios to speak to those on the same road/highway that they are traveling on. If you are speaking with someone in front or behind your vehicle and either one of you take a turn and leave the more powerful RF lobe, a definite change in clarity will be noted. The second advantage of phased antennas is their ability to perform where there is little reflective ground plane for the single antenna to radiate its energy from. For instance, on fiberglass vehicles or those with light aluminum sheeting over a non-metallic frame. In those situations a phased set-up allows the antennas to use each other's radiation field to direct the combined energy across the horizon. In order to be effective at least 2/3's of each antenna must have unobstructed line-of-sight to the other antenna. EXCEPTIONS No ground plane antenna systems can be used in a dual configuration but they do not perform in the same manner as the ground plane dependent, dual antenna systems. Instead of depending upon each other to radiate energy, the NGP's in dual configurations act independently from one another. While there will be some pattern distortion when compared to a single antenna installation, it will be minimal. Dual NGP's use 50-ohm coax that is specifically wired in a manner that allows the coax itself to be used as the reflecting element. The coaxial circuit limits the power that the system can dissipate to less than 200 watts. The primary reason for using dual NGP's would be for the purpose of maintaining an Omni-directional pattern without blind spots caused by blockage from a high profile vehicle. http://www.firecommunications.com/