Remedial Procedures

TM 11-490-5

identification of cable grounding problems consists of

(b) Initiate action for possible sector

disconnecting the cable between the sites and

blanking of the radar signal or other reduction in the

measuring the resistance between pairs and the

radiation of this signal.

resistance to ground for each cable pair. A suitable

ohmmeter, impedance bridge, or megger can be used

site or the radar, if practicable. In some cases, the

for this test. Interpair resistance indications of less than

solution could be as simple as a relocation of receive

10,000 ohms per loop mile or resistance readings to

antennas.

ground of less than 50,000 ohms is normally indicative

(3) Office equipment. Qualified repairmen

of a faulty cable or cable pair. Coaxial cables are very

must be consulted to eliminate problems from these

susceptible to damage caused by heat, compression, or

machines, including the assurance that the internal

abrasion.

When these occur, the results can be

ground

connections

are properly

maintained.

mismatches, loss of desired signal, or introduction of

Procedures follow:

interfering signals. A floating shield caused by damage

(a) Identify specific equipment causing

to the cable may result in unwanted signals being

problems. A 3-wire power cord properly grounding the

introduced into or radiated from the equipment or cable.

equipment may solve the problem. If it does not,

(b) Report interference.

multiband radio is available, use it to trace the source of

powerline problems, particularly if a defective insulator

relocation.

or transformer is suspected as the source. Usually,

(4) Power lines.

such interference will increase in intensity as the source

is approached with the radio. Poor ground connections

(a) Isolate the cause of interference to

at the power poles can result in a power frequency hum

the most likely source, such as a power transformer or

in the communications equipment as a result of the

insulator, with procedures given in paragraph 43c(3)(c).

common impedance in the ground loop. A rapid means

(b ) Report this information to the

of isolation, if this is suspected. particularly in dry,

responsible authority, such as the local facility engineer.

sandy soil, is to thoroughly wet the ground around power

(5) Cables.

Damaged cables must be

poles close to the station with a saline solution. If the

replaced, or spare cables used. When the cause of the

problem .is powerline grounding, the interference will be

cable damage has been determined, appropriate steps

reduced or eliminated. In the case of a broken insulator.

can be taken to ensure that it does not happen again,

hitting the suspected pole with a sledgehammer will

including the erection of signs and barriers to prevent

cause a variation in the interference.

vehicular traffic over the cables. Corroded and loose

d. Remedial Procedures. The procedures which

connections can be corrected by cleaning and

operating personnel can use in the correction of

tightening. If this is not possible, reroute to another

interference problems may be limited by available test

cable pair, if available.

equipment and maintenance level authorization. The

(6) Circuit components.

Problems which

following procedures, where authorized. may be used

have been traced to faulty circuit components, such as

for the correction of the corresponding interference

line amplifier modules.

will generally require the

sources given in paragraph 4-3b (2) (b ):

services of a repairman to test at the appropriate

(1) Ignition noise.

monitoring jack and replace or adjust as necessary.

(a) Identify the source of the ignition

Patching may be required to bypass the particular

noise to the specific source such as privately-owned

equipment involved while this maintenance is being

vehicles, lawn mowers, or similar gasoline-powered

performed.

engines.

(7) Equipment grounding.

All electrically

(b) Report this information to the level

operated equipment within the site must be maintained

where remedial action can be taken. Such action may

at ground potential by interconnection with the common

include restriction of the ignition noise sources from the

station ground. At DCA facilities, a station ground must

communication site, installation of noise suppresser

be maintained at the DCS standard and periodically

devices, or restricting their use to periods of low

measured by the supporting maintenance or engineering

communications usage.

facility. Non-DCS transportable or mobile installations

(2) Radar. Radars are sometimes located

also require good grounds. but have special grounding

where they will sweep the area of a communications

problems associated with their temporary deployment.

site. In the event that radar interference is encountered,

Grounding rods furnished with the equipment may not

the following procedures should be followed.

suffice in some areas. In sandy soils. use of buried

copper plates to increase the contact area with the soil

(a) Report interference to proper

may be necessary. Also, all grounds may require

authorities.

regular attention in accordance

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