Telex 38109-977 manual Design of Wireless Intercom Systems

C H A P T E R

7

DESIGN OF WIRELESS

INTERCOM SYSTEMS

TOM TURKINGTON

Introduction

The design, and subsequent operation, of a wireless intercom system is, like any wireless network, highly dependent on numerous factors. Some of these factors you will have control over, but many you will not. The key to successful wireless system design, whether it be intercoms, talent audio, or roving camera, is to gather the information related to all of the variables before you get started and then match the system components and architecture to your specific requirements. There is no such thing as a one size fits all wireless system. In this chapter, we explore some Radio Frequency (RF) theory that allow you to have a better understanding of how RF works. We will also look at many of the key components of a wireless communications system and how they go together to create the desired effect.

Back-to-Basics

In this section, we discuss the theory of how RF signals act and how they are affected by various conditions. There is some math discussed here, but only enough to convey the principles at hand. The idea is to give you a good working knowledge of RF principles, not make you an expert in Bessel functions. Old RF pros can probably skip this section, although a refresher of this material is almost always appropriate.

First, let’s answer the question, “What is RF?” Contrary to popular belief, the frequency of a signal does not determine whether it is an RF signal or not. The defining factor for RF signals is the medium through which they propagate. All energy that travels in waves propagates through some medium which allows the wave to move from one location to another. In the case of sound, the medium is typically air or water or some other physical mass. RF signals on the other hand, regardless of frequency, always propagate or move through the electromagnetic spectrum. Where as sound needs some physical mass to move, RF signals do not. The electromagnetic spectrum exists everywhere (as far as we know), and enables RF signals to move through the vast vacuum of space where sound waves could never go.

C h a p t e r 7 - D e s i g n o f W i r e l e s s I n t e r c o m S y s t e m s 95