TH-3 Medium-Haul Application: Frequency-Diplexed Auxiliary Channel

Point-to-point microwave radio systems require surveillance and maintenance to insure high-quality performance and reliability. This is accomplished by having access at each of the radio stations to an order-wire facility and a surveillance and control system, as well as other various special purpose circuits. The electrical signals associated with these circuits are typically carried to and from the radio stations over 3-KHz voice-frequency circuits. Three possible ways of transmitting these signals are to carry them over voice-frequency land lines, on a separate microwave channel, or directly on the payload microwave channel. Land lines have been widely used in the past, but have two major disadvantages. Often the land lines between radio stations may follow a long circuitous route over a wide variety of transmission facilities. Secondly, they are relatively costly, especially if construction of new lines is required to provide access at a remote radio station. The question of cost is particularly important when one talks about lowor medium-density routes where the cost of the equipment required to perform these functions is spread over a limited number of telephone circuits. The use of a separate microwave channel (auxiliary channel) has gained popularity in recent years. It frequently provides transmission 2287