Editorial/And then there were 14–plus the IWCE trade show
Mobile Radio Technology makes its home among trade magazines owned by Intertec Publishing, a 110-year-old company with its headquarters in Overland Park, KS, and offices elsewhere in the United States and Europe. Until Dec. 15, 1995, Intertec’s telecommunications, broadcasting and electronics magazines numbered 11. On that date, Intertec acquired the assets of Argus Inc., an Atlanta-based publishing company, adding seven more telecommunications and electronics magazines, among other properties. The magazines are Communications, Cellular Integration, Voz Y Datos, PCS Today, Mobile Computing Technology, Satellite Communications and RF Design. Altogether, properties acquired from Argus include 36 magazines, 27 directories and four other periodicals. Before Dec. 15, Intertec already published 46 magazines and newsletters, as well as numerous books that include pricing guides, directories and repair manuals. Both companies counted trade shows among their products, too. Among the trade shows acquired from Argus is the International Wireless Communications Expo (IWCE). On Jan. 22, the decision was made to discontinue publishing Communications, Cellular Integration, Voz Y Datos and PCS Today. Our company president, Raymond E. Maloney, cited the magazines’ competitive nature with existing Intertec magazines as the reason. One other former Argus magazine that serves another industry was closed for the same reason. As a result, we had to say goodbye to two editors with whom we previously competed in covering the industry and who had been co-workers for only a short time, Communications editor Kelley A. Richardson and managing editor Monica Alleven. We’re happy to say that Communications business and technology editor Amy Cosper has transferred to Satellite Communications, and Voz Y Datos associate publisher and editor Elsa Saavedra continues as part of the team involved in organizing the IWCE conference. Also, we welcome Mobile Computing Technology editor Tom Parrish, RF Design editor Gary A. Breed and Satellite Communications editor James M. Gifford, among all our other new colleagues who come to Intertec as a result of the transition. OK, so Intertec is a player in these “mergers and acquisitions” that we all hear about. What difference does it make? The growth in the number of Intertec telecommunications magazines and trade shows can help both you and our advertisers.
Trade shows Intertec owns or co-manages about 30 trade shows. Among its trade shows are WirelessWorld (co-sponsored with E.J. Krause) and, perhaps as the most enticing part of the Dec. 15 acquisition as far as MRT readers and advertisers are concerned, IWCE. MRT has become the official publication of IWCE. It will be much easier to publish information useful to you that may be developed at IWCE conferences. Conversely, you and our editors, writers and editorial advisers will be able to contribute ideas to future IWCE conferences, and some will take active roles alongside the current IWCE conference supporters. We’re also anticipating that any IWCE exhibitors not already taking advantage of MRT to tell you about their products and services will see yet another reason to do so, whether through editorial information, advertising or both.
Magazines You’ll benefit from the growing list of Intertec telecommunications magazines because editors can pool their resources for special projects. Examples include special newspapers (known as “show dailies”) distributed at trade shows such as CTIA and PCIA. Sometimes news and feature articles developed for one magazine can be modified and tailored for another to make use of the best sources developed by each editor. Advertisers benefit from discounts for doing business with multiple Intertec publications, the efficiency of using one publisher for many of their ad placements and the access to vertical markets. You usually tell us that you look forward to reading our advertisements to find products and services you can use. Should we say this? Some readers tell us they like the advertisements as much as what we write. Ouch. Or, hurray. Ummm, how do we take that? Anyway, when more advertising results from the new advantages Intertec can offer, you benefit, too. We welcome our new colleagues (600, altogether!) from the former Argus properties, and we plan to offer you even better editorial and trade show services in 1996.
K-III Communications Intertec, by the way, is a wholly owned subsidiary of New York-based K-III Communications, a publicly traded Fortune 500 company. Intertec is the trade magazine unit in K-III’s family, which includes other subsidiaries that specialize in consumer magazines, electronic mass media and other information services. –Don Bishop
Which antenna is best suited to your radio coverage needs? The answer to this question requires some basic knowledge of base station antennas as well as a detailed study of your particular coverage requirements and interference possibilities and probabilities. The antenna tower must be able to support the chosen antenna. (Many antenna towers are heavily loaded with antennas, and the addition of one more antenna can be critical.) The loading effect of the antenna on the supporting structure (tower) must be considered. The height of the antenna can not exceed the FCC-licensed antenna height (to tip). The antenna must not cause the system to exceed the FCC-licensed effective radiated power (ERP) limitation. (This is one FCC regulation that many system designers/users often seem to overlook.) Before going any further, some of the basic electrical specifications that must be considered in choosing the proper base station antenna for your radio system are described in some detail.
Basic electrical specifications There are many factors about antennas that must be taken into consideration before setting out to choose the antenna for the desired coverage. A few of the more important base station antenna specifications are described here–not necessarily in order of importance to your particular requirements. Gain — It is a law of physics that you never get something for nothing. This applies to antennas, too! An antenna is a passive device. To achieve gain in one direction, the energy is taken from another direction. Antenna gain is obtained by simply redistributing the energy in the desired direction or plane. The gain occurs only in the desired direction or plane. The total amount of energy being radiated from the antenna is not increased. In mobile radio systems, where vertical polarization is used, any radiation upward or downward is usually undesirable. (Sometimes some downward radiation is needed, so downtilt is used to fill in certain areas. Because mobile antennas are vertical, the base antenna polarization must be vertical. Any energy radiated upward from the base station is wasted. Figure 1 to the left shows how the stacking of antennas (vertically) compresses the upward radiation into a lower angle of radiation, thus concentrating the energy toward the horizon, where it is needed. Antenna gain is usually referenced to a halfwave dipole. For example, if an antenna has a 3dB gain compared to a halfwave dipole, the gain specification figure will be written as 3dBd, where the d signifies dipole. The halfwave dipole serves as the reference antenna for the gain figures. Sometimes you will see gain specification figures based on the isotropic radiator as the reference. An isotropic radiator is a hypothetical sphere with equal radiation from any point on the sphere. The sun can be considered an isotropic radiator. On earth, a true isotropic antenna does not exist. When the isotropic radiator is the reference for gain figures the gain should be written as dBi, where the letter i signifies isotropic radiator. A halfwave dipole has a gain of 2.15dBi (2.15dB compared to the isotropic radiator). Any antenna referenced to the isotropic radiator will have higher apparent gain than an antenna referenced to the halfwave dipole. That is why it is so important to know what reference antenna is used for gain specification figures. It would be good if all manufacturers used the same reference antenna for gain figures or at least included the reference dBd or dBi with the figures. However, sometimes you will find specifications such as “antenna gain is 7dB.” If the dipole is the reference antenna, the gain is 7dBd. If the reference antenna is the isotropic radiator, the antenna gain is 7dBi, which is equivalent to 4.85dBd. VSWR — The voltage standing wave ratio (VSWR) of the antenna should be as low as possible to maximize antenna system efficiency. The best possible VSWR is 1:1. The generally accepted figure for antenna VSWR is 1.5:1. This represents a good match between the antenna and the transmission line. A good match means that little power will be reflected back down the transmission line. In terms of forward and reflected power, this VSWR represents a forward-to- reflected-power ratio of 25:1; that is, for every 25W reaching the antenna only 1W is reflected back down the line. To convert VSWR to forward-to-reflected-power ratio, use the following formula: R=1/[S-1/S+1]2 where S = VSWR. (See the graph in Figure 2 on page 8 for converting between VSWR and forward-to-reflected-power ratio.) Bandwidth — The bandwidth for an antenna is the frequency spread over which the VSWR will not exceed a given level–usually 1.5:1. Sometimes the bandwidth is given for a VSWR of 2:1 also. Be sure you know which VSWR figure is the one being used as a reference for the bandwidth figure. The bandwidth figure might be listed as a percentage or a frequency spread. For example, if the bandwidth specification figure is 10MHz, this means that the frequency of operation over which the VSWR does not exceed 1.5:1 (2:1, in some cases) is 5MHz above or below the center or resonant frequency of the antenna. If the figure is listed as a percentage, the percentage figure must be multiplied by the center frequency of the antenna. For example, an antenna tuned to 150MHz with a bandwidth of 6% would have a total frequency spread of 9MHz or +/-4.5MHz. This means that the antenna can be operated over a frequency range of 145.5MHz to 154.5MHz without exceeding the given VSWR figure. The VSWR graph in Figure 3 on page 60 illustrates the operating bandwidth in graphical form. Beamwidth — This discussion applies only to vertically polarized antennas. This specification is used to define the width of the main lobe or beam in the horizontal or vertical plane. For omnidirectional antennas using vertical polarization, this applies only to the vertical plane. For directional antennas this would also apply to the main lobe(s) in the horizontal plane. The beamwidth is defined as the difference in angular degrees between the two half-power (-3dB) points on the main lobe. This can be better understood by referring to the illustration in Figure 4 on page 62. This is the horizontal (azimuthal) radiation pattern for a beam (yagi) antenna. Note that at the two points indicated on the pattern, the signal level is 3dB below the maximum point of the main lobe. Generally, for a yagi antenna, the beamwidth drops and the gain increases as the number of elements increase. Front-to-back ratio — The front-to-back ratio specification is for directional antennas such as the yagi and the corner reflector. It is simply a comparison of the radiation level from the front and back of the antenna. If the antenna is positioned so that the main lobe is at 0 degrees, the back side radiation is measured at 180 degrees. The front-to-back ratio can be quite important in choosing the proper antenna for a radio system. The front-to-back ratio can be better understood by referring back to Figure 4. These are just a few of the basic electrical specifications with which you should be familiar. In addition to the electrical specifications of an antenna, the mechanical specifications can be quite important. Some of the mechanical specifications will be covered next time, as well as choosing the correct antenna for various applications, each with its own problems. Until next time–stay tuned!