there are literally thousands of these networks now in operation. Another application that has promise of wide deployment is large families of low earth orbit (LEO) satellites. Motorola developed and fielded Iridium that could provide worldwide cellular/PCS coverage. Because of LEO's low-altitude orbit (about 785 km above the earth's surface), the notorious delay problem typical of GEO (geostationary satellite) is nearly eliminated. Iridium worked perfectly. It was the marketing effort that failed. The system was sold at a fire sale at pennies on the dollar. Our opinion is that Iridium was too early for its time. 9.2.3 Line-of-Sight Microwave 9.2.3.1 Introduction. Line-of-sight (LOS) microwave provides a comparative broad- band connectivity over a single link or a series of links in tandem. We must be careful on the use of language here. First a link, in the sense we use it, connects one radio terminal to another or to a repeater site. The term link was used in Figure 9.1 in the "network" sense. Figure 9.2 illustrates the meaning of a "link" in line-of-sight microwave. Care must also be taken with the use of the expression line-of-sight. Because we can "see" a distant LOS microwave antenna does not mean that line-of-sight clearance has been complied with. We can take advantage of this "line-of-sight" phenomenon at frequencies from about 150 MHz well into the millimeter-wave region. 1 Links can be up to 30 miles long, depend- ing on terrain topology. I have engineered some links well over 100 miles long. In fact, links with geostationary satellites can be over 23,000 miles long. On conventional LOS microwave links, the length of a link is a function of antenna height. The higher the antenna, the further the reach. Let us suppose smooth earth. This means an earth surface with no mountains, ridges, buildings, or sloping ground what-so- ever. We could consider an overwater path as a smooth earth path. Some paths on the North American prairie approach smooth earth. In the case of smooth earth, the LOS distance from an