Extending mobile radio range by VHF repeaters

Abstract

The distance from a base station over which a mobile radio may operate is usually limited to near the optical horizon, particularly with frequencies of 150 mc and higher. When it is desired to extend the mobile range beyond this distance remotely controlled base stations involving either telephone lines or microwave relay systems are used quite successfully. However, these systems are expensive, particularly where the cost of the microwave system or telephone line cannot be shared by other functions such as additional telephone channels or telemetering and control channels. By the Judicious use of mountain tops, where available, and the use of unattended automatic repeater (relay) stations, it is possible to extend mobile range from a base station to several times that which is obtained with a single base station without incurring the expense or complexity involved in a microwave relay system. This paper will describe some of the methods which have been used by the Bureau of Reclamation to provide this type of long distance base to mobile coverage. The operations of the Bureau of Reclamation differ somewhat from the average public utility in that the transmission of power or water is on a wholesale basis with very little retail or distribution type operation. Rather than involving a small amount of high voltage transmission with a great deal of complicated distribution which requires a large number of mobile units in a relatively small area, as is the case with most power utilities, the Bureau's power transmission systems involve very long high voltage power lines with few operational centers or base stations and relatively few mobile units, but these mobile units are required to operate over the much greater distances involved. Similarly, the Bureau's large irrigation systems involve transportation of water over hundreds of miles. This also requires a system with relatively few mobile stations but with a requirement that these stations operate over rather long distances. For these reasons it has been necessary to provide unattended vhf repeaters to extend mobile coverage from the operating centers to the ends of the power or water transmission systems. Since most of the Bureau of Reclamation operations are carried on in the sparsely settled areas of the 17 western states, there is often a lack of commercial telephone facilities which could otherwise be used to interconnect operating centers and provide channels to extend radio coverage. Three general types of repeater systems are used. (1) The low band-high band system which utilizes mobiles operating in the low vhf band (approximately 30 mc) with relay links in the high vhf band (approximately 160 mc). (2) The high bead system with wide frequency spacing. (3) The bigh band system with close frequency spacing. One of each will be described.