The advantages of close spacing

It also is important for the RF engineer to become familar with the FCC's Form 601, which is used for all Part 90 applications, and which consists of 3 segments. The main form is 4-pages long and lists the type of application, the licensee's name, contact person, mailing address, telephone contact number and e-mail address. It also asks some questions about ethnicity and ownership, and informs the signatory that he is under the penalty of perjury should lie on the form.

Let's now review some of the specific elements of Form 601.

SCHEDULE D Form 601 Schedule D lists the particulars of a site location. A site can be a base fixed site, itinerant site, mobile, control station, or a repeater. There can be a maximum of 6 fixed sites for each license. If there are more than 6 fixed sites, then a second license is required.

Other pertinent information includes the latitude and longitude of the site for fixed sites, (accurate within 1 second), ground elevation, structure height, maximum height with antennas, structure type, area of operation for mobiles, and information related to coordination with Mexico or Canada. Also, in the last year, because of migratory birds, the distinction between guyed towers and free-standing towers also must be included with the information regarding antenna structures required by the form.

SCHEDULE H Schedule H asks about the purpose for the license, the coordination information, the linking to other licenses, the control-point information, the antenna height, antenna gain, antenna direction, ERP, frequency, modulation, and antenna number.

FORM 159 Public-safety agencies are exempt from fees for license applications. Commercial and private entities are not exempt and they must use Form 159, which has the pertinent name and registration information, as well as the credit-card information for any payments.

All of the forms and their instructions are available on the FCC's website, www.fcc.gov. For the different services, such as land mobile radio, cellular, paging, air-to-ground, marine, and microwave, you can review the Form 601 located at the website to learn more about the schedules that are required for the different types of services and applications.

When making measurements to see how strong a signal is at a given point, an antenna can be mounted in the center of the roof of a vehicle and the coaxial lead is connected to the antenna input lead of a communications service monitor, spectrum analyzer, or receiver with a calibrated RSSI meter. In addition, the line loss of the transmission line at the operating frequency must be known and added into the reading, and if a gain antenna is used, that must be subtracted from the reading. Because of Rayleigh fading, the signal-strength reading must be made multiple times, and an average obtained, in order to eliminate the effects of the fading in a given location. To ensure that interference doesn't affect a given signal, there should be at least a 13 dB difference between the desired signal and the interfering signal in most situations.

All of the methods described in this article allow radio frequency engineers, frequency coordinators, regional planning committees and the FCC determine whether base-station sites can be located as close as possible without causing interference. By using geospatial data and RF-planning tools, this separation can be optimized to allow sites to be placed as close as possible, in order to minimize the number of sites needed to cover a service area and save resources.

Ira Wiesenfeld, P.E., has been involved with commercial radio systems since 1966, and has experience with land-mobile-radio, broadcast, paging and military communications systems. He holds an FCC general radiotelephone operator's license, Extra Class amateur license, and is the author of Wiring for Wireless Sites, as well as many articles in various magazines. Wiesenfeld can be reached at iwiesenfel@aol.com.

Robert C. Shapiro, P.E., is a consulting engineer who has been in land mobile radio engineering — including public-safety and transportation communications — since 1984. He serves on the TIA TR8 committee (TSB-88) as vice chair and is a senior member of the IEEE. He can be reached at bshapiro@ieee.org.