CHAPTER 4. DETECTION, RECOGNITION, ISOLATION, AND REMEDY OF EMC PROBLEMS

TM 11-490-5

CHAPTER 4

DETECTION, RECOGNITION, ISOLATION, AND

REMEDY OF EMC PROBLEMS

assistance and to report promptly any problem outside

4-1. General

their experience.

The following list, although not

EMC problems at fixed Defense

exhaustive, contains some of the "tools" available to

Communications System (DCS) installations or at fixed

operating personnel:

or transportable non-DCS facilities may be grouped into

two broad categories:

(1) Test equipment.

(1) Instrasite EMC problems associated with

(2) Testing and isolation procedures.

the equipments and installation which generally require

(3) Equipment alignment procedures.

some type of maintenance to resolve.

(4) Backup or spare equipment and modules.

(2) Intersite EMC problems when the

(5) Patching and rerouting techniques.

interference originates at some location other than the

(6) Interpretation of equipment meters and

communications site.

indicators.

b. A DCS station is a vital link in a chain of

(7) Antenna orientation.

communications which may provide service between

(8) Communication training.

local subscribers or between far-distant points and local

subscribers, and may interface with non-DCS facilities.

(9) Substitution.

The station .may handle clear-text or encrypted

(10) Signal tracing.

transmissions. The stations may be connected by radio

(12) Experience of senior operating personnel.

propagation media only, or in combination with cable

(13) Equipment history (log books and the

circuits. However, with the exception of unattended

like).

relays, stations are manned by operating personnel who

are vital in maintaining successful communications

4-2. Discussion of EMC Problems

when interference is experienced. At most stations,

a. Introduction.

some incidence of EMC problems may be anticipated.

(1) When a communications site is installed,

These problems may originate at some location not

intrasite conducted emission problems have normally

associated with the communications site, they may be

been reduced to acceptable levels by proper grounding,

the result of enemy actions, or they may originate within

equipment location, and similar installation procedures.

a station. When new equipment is procured, extensive

However, normal deterioration will occur over a period

EMC tests are made in an effort to eliminate EMC

of time, corrosion may form on grounds and other

problems.

However, these tests do not always

terminals, connections may develop higher resistances

reproduce all conditions in an actual installation. During

than normal, and components may degenerate or fail

acceptance tests of a new installation, it may not always

without causing an apparent equipment malfunction. All

be possible to make a complete test covering the entire

of these conditions may cause interference. These

frequency range which is to be used in operation. As

interference problems can normally be avoided or

they age, components drift out of tolerance and

minimized

proper

preventive

maintenance

sometimes fail completely; when this happens, rapid

procedures.

action must be taken to isolate, locate, and repair or

(2) One major cause of operational EMC

replace the component. The human factor is thus of

problems is radiated signals from sources beyond the

vital importance in the solution of EMC problems.

local C-E site. This type of intersite interference is

c. To facilitate rapid solution of EMC problems,

difficult to isolate or minimize. It may be unintentional

operation personnel must be familiar with all facets of

interference from friendly (or enemy) radio or radar

their station. They must understand its scope and

transmitters, or it may be intentional jamming or

capabilities, be familiar with normal indicator readings

intrusion.

(as they usually provide the first indication of any

problems), and be conversant with the use of available

(3) Although interference may originate from

equipment. Operating personnel must also learn to

an RF source, it usually manifests itself as a faulty

recognize situations which require more skilled

operating condition in a subscriber's instrument. It

4-1