9.7.1 Introduction

Video signals are distributed by video distribution amplifiers (DAs). These are wide-bandwidth amplifiers designed to drive the low-impedance, unbalanced (75- ? nominal) coaxial cables used in television facilities. Video DAs typically provide bridging (high-impedance) inputs with two paralleled input connectors to allow the input signal to be looped through to additional equipment and ultimately terminated in 75 ?. They also normally provide multiple, isolated 75 ? source-terminated outputs to drive distribution cables for one or more destinations.

There are three basic types of DAs, designated by their intended use as video DAs, subcarrier DAs, and pulse DAs. Video DAs are designed to accommodate standard 1-V (nominal) peak-to-peak (p-p) composite or 0.7 V (nominal) p-p noncomposite video signals. Some video DAs may be used interchangeably as subcarrier DAs because they have sufficient headroom to accommodate the 2-V p-p (nominal) terminated or 4-V p-p unterminated subcarrier signal levels. Pulse DAs typically accommodate up to 4-V p-p (nominal) pulse signal inputs and may provide shaped output pulses having controlled rise and fall times.

Subcarrier and pulse DAs may be further categorized as being linear or regenerative. Linear DAs linearly amplify the signal, whereas regenerative DAs replace the original sync, burst, and blanking portion of the signal with a regenerated version.

9.7.2 Video Distribution System Development

Standard transmission line practice requires that a low-impedance, shielded coaxial cable be used to transmit wide-band video signals in order to minimize overall signal loss, frequency response roll-off, and...