Noise and intermodulation problems in multichannel closed-circuit television systems

In the past decade there has been a rapid growth in communication facilities designed to transmit television (TV) signals relatively short distances over coaxial cables. These systems handle six or more video signals which amplitude-modulate (AM) r-f (radio-frequency) carriers in the 8- to 220-mc (megacycle) range. The associated audio signals frequency-modulate (FM) r-f sound carriers whose rest frequencies are 4.5 mc away from their associated picture carriers. These systems are used for industrial, educational, and entertainment purposes, and descriptions of many of them have appeared in the literature.1¿3 This paper will discuss two problems that affect the design of any closed-circuit TV system: thermal noise and intermodulation products created by amplifier non-linearity.