DCS (Fixed Installation ).

TM 11-490-5

may first be reported by the subscriber, or be discovered

antenna; use of a more highly selective receiver, if

during routine circuit checks.

available; or use of a frequency-synthesized receiver

b. DCS (Fixed Installation ).

instead of the automatic frequency control type,

(1) In the case of a fixed DCS system, the

providing the distant wanted transmitter is also

equipment is normally installed in accordance with I)('A

frequency-synthesized).

standards and other installation criteria. Any deviation

c. Non-DCS (Transportable).

from these standards is corrected or a waiver is

(1) In the case of non-DCS transportable or

recorded when the system is accepted and placed in

mobile systems, each time the equipment is moved and

service. Daily logs concerning equipment performance

reinstalled, new problems may be experienced.

are maintained and a history of any discrepancies and

Although general performance criteria are available for

corrective action taken are recorded.

Therefore,

both equipments and systems, performance at

operating personnal at a DCS fixed site have both the

individual locations will vary. Equipment logs can

standard performance criteria for the particular

provide some insight into past performance of the

equipment and the past history of the performance of

equipment and are useful in establishing performance

the facility. If operating personel are cognizant of the

criteria. However, the experience of the personnel

past performance of the system, as recorded in the

assigned to the system as to normal performance under

station log, they can readily recognize any deviation

similar geographic, soil (ground considerations), and

from normal performance. The data also provide

distance conditions is the most significant factor in the

information on whether the problem is a recurring one

recognition and isolation of an EMC problem.

and what corrective action was previously taken. The

data may also assist in the isolation of the problem and

(2) Intrasite EMC problems at a non-DCS

a determination of whether it is an EMC problem or

transportable or mobile site are more prevalent than a

equipment malfunction.

fixed site, because equipments are subject to movement

and reinstallation, and therefore cables and connectors

(2) Intrasite EMC problems can often be

experience greater wear and breakage. Each new

traced to a lack of adequate preventive maintenance

installation has a potential for problems with connectors,

which can result is partial or complete failure of

terminals, antennas, primary power, grounding, and

components.

either

causing

electromagnetic

interconnections. The methodology for isolation and

interference (EMI) or increasing EMI vulnerability. The

location of these types of EMC problems is similar to the

usual cause of loose connections.

poor ground

fixed site, but the probability of occurrence is much

connections, corroded terminals. cold solder joints, and

greater.

faulty cables is lack of proper maintenance. It is worth

noting that the installation of new equipment with

(3) The source of intersite unintentional

accompanying cables and jumpers can be the cause of

interference at a non-DCS transportable or mobile site is

EMC problems not previously present. Existing cables

also more difficult to isolate and locate than at a fixed

not associated with the new installation can be relocated

site. Since the system is the new element in the area.

or damaged to the degree where interference occurs.

the number and location of potential interferers in the

All new installations or replacement work should be

area are unknown unless an extensive site survey and

checked for their effects on other circuits.

frequency monitoring have first been performed.

(3) Intersite unintentional interference at a

d. Unintentional EMC Versus Intentional ECM

DCS fixed site is generally caused by installation or

Problems.

operation of new equipment, new frequency

(1) When outside interference is detected,

assignments, or weather conditions. This results in a

the operator must determine whether the problem is

site becoming more vulnerable because of physical

attributable to unintentional causes or whether jamming

changes at the site (such as grounding) or abnormal

or intentional intrusion is occurring. Where the latter is

propagation (such as ducting). Frequently, when this

suspected, any action taken must be such as to deny

occurs, the interfering source may be identifiable from

the enemy any intelligence regarding the effectiveness

frequency assignments. However, if the interfering

of his actions, or the fact that they have been detected.

frequency is assigned to the intefering station, and the

(2) The procedures for dealing with enemy

latter is operating within authorized bandwidth, mode,

action are prescribed by AR 105-3, "Reporting

and emitted power limits, the solution will lie in obtaining

Meaconing, Intrusion, Jamming, and Interference (MIJI)

a different frequency assignment for one station or the

of Electromagnetic Systems;" AR 105-87, "Electronic

other. If this is not possible, steps must be taken to

Warfare;" and DCAC-310-70-6, "Jamming or Sabotage

minimize the degree of coupling (for example, slight

of DCS Telecommunications Facilities."

rotation of receive

4-2