TABLE OF CONTENTS The previous sections of this chapter have introduced a variety of system measurements and some of the necessary hardware. In this section, we cover the instruments in a surveillance system in more detail, leaving the requirement of the control hardware and software for later discussion.
The instruments to be used are
SLMS
Access switches
Level generators
Telephone/data line analyzers
We shall discuss these in turn, beginning with the most important unit, the SLMS.
The traditional manual SLMS was simply a wave analyzer, with a set of measurement filters chosen to suit the FDM signals. An instrument that can also be used by a computer has to be easier to use than a traditional set, which pleases the manual user. Let us examine why this is so.
The SLMS can be considered as a tunable bandpass filter, which selects the desired signal, and a level detector to measure the signal power. In practice, a frequency changer tunes to the desired signal, and the measurement is made at a fixed frequency. The instrument is, in fact, a super-heterodyne radio receiver.
The traditional SLMS bore a closer resemblance to a domestic radio than a complex measuring instrument. It was tuned by turning a knob and reading out the approximate frequency on a dial. The measured result was obtained from a combination of attenuator knob settings and meter readings. The meter usually had to be peaked to obtain an accurate reading,...
