PL75-9 datasheet(86/141 Pages) ETC

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Electronic systems wiring & cable

Systems are often designed, fabricated, and installed using the simplest

multi-wire cable or grounded coax between equipment, racks, and build-

ings, not realizing that they will probably encounter and pick up all

manner of interference. Nearby electrical equipment such as high power

radar, broadcast stations, power distribution mains, fluorescent light-

ing, arcing motors, teletype and communications circuits are but a few

of the noise makers. The lower the system signal voltage level, the

greater is the susceptibility to this outside interference.

A system design might work fine on paper or when initially assembled

and tested. But it may not perform as anticipated when installed at its

final location on ship or shore. You may realize that the completed sys-

tem has picked up much noise and hum, or is itself radiating interfer-

ence so heavily that the equipment is unusable. Costly additional ef-

fort, parts, and time expended to locate and attempts to eliminate the

causes of the noise pickup may meet with little success. Cable-to-equip-

ment interface engineering should be applied at the start of system plan-

ning and design to avoid this unnecessary waste. This applies to all

systems for low or high frequency signals, for applications in TV, te-

lemetry, timing, ordnance, environmental testing, computer, telephone,

test instrumentation, or normal communications. Each system must

be considered individually, since the signal frequencies and amplitudes

within the system and the anticipated external interference will dictate

what type of cabling and connection techniques are to be used.

Examples of Good Cable Engineering

Low-level environmental systems predominantly use “guarded” bal-

anced and shielded lines to transmit the calibrated transducer test volt-

age to an isolated charge amplifier.

TV video is distributed over 124-ohm “shielded twisted pair” (twinax),

instead of coax, in high noise areas to cancel low frequency magnetic

field cross-talk and hum.

Digital applications in the computer and instrumentation fields re-

quire good high-frequency design engineering when transmitting nano-

second rise time pulses. A 10 nanosecond rise time pulse is equivalent

to 100 megahertz RF. Using good coax cabling techniques helps to

avoid pulse reflection, false noise triggering or data inaccuracy.

Special care is required to keep noise from entering information sys-

tems (particularly aircraft). Low level communication circuit cabling

should be space separated and have effective shielding from adjacent

parallel power circuits to avoid induced hum.

Unprotected circuits (such as ordnance and timing) can receive false

pulsing if exposed to external radiated RF interfering fields.

High megawatt pulsed radar will introduce both its carrier and pulsed

radio frequency waveform into nearby sensitive low-level unprotected

cable runs which act as receiving antennas.

Sometimes the transmitted pulses have amplitudes of hundreds of thou-

sands of volts (as used in atomic energy testing or linear accelerators)

thereby producing large magnetic and capacitive interference fields.

These play havoc with local cable-connected instrumentation and elec-

tronic equipment.

Connector attachment : Crimping or Soldering

Crimping is normally used where the speed of attachment is im-

portant or where it is virtually impossible to solder due to lack of

power (as on the top of a telephone pole or in a cable vault). A

special crimp tool quickly and simply installs the connector to the

cable. Repair requires a new connector for replacement. Solder-

ing, on the other hand, does not require any special tool. A sol-

dered connection will not corrode provided adequate heat is cor-

rectly applied to avoid a “cold solder joint.” Some soldered coax

connectors may be used over without special tools or replacement

parts. This is advantageous on shipboard or in field locations where

replacement parts or tools are not always available.

Noise

Electrical noise is by definition, any unwanted interfering voltage,

developed within or externally to a system, which reduces the

performance of that system. "Noise" has always been a problem

and in the past was usually reduced by brute-force filtering which

reduced or stopped "noise" after it had entered the system. This

method was quite expensive, but reasonably effective since signal

information voltages were low in frequency and systems were few

and not too large or complex.

Present day communication and data systems are continually be-

coming larger, more numerous and use higher information rates

and frequencies in an atmosphere of expanded electrical and elec-

tronic equipment usage. The net result is ever increasing levels of

interference and noise which creates an electronic traffic jam of

major proportions. This applies equally to low level analog and

digital pulse systems. Filtering is practically useless (or in some

cases, completely unusable) since it produces excessive deteriora-

tion of the desired pulse waveforms or inaccuracies and distortion

of analog signal voltages. Noise reduction is best accomplished

by simply stopping "noise" before it enters the system.

The following describes how external noise is introduced into sys-

tems by the equipment interconnecting wiring, and the improve-

ments that can be realized by installing noise-rejecting type cables

and applying good equipment isolation and grounding techniques.

Most electronic equipment does not produce random noise and usu-

ally performs the singular task it is designed to do. Unwanted noise

is picked up by the interconnecting wiring through the direct con-

tact action of ground loops and common mode returns, or by in-

ductive and capacitive pickup of nearby radiated fields. A desired

signal in one circuit can be noise to another. Interference can be

produced by local circuits within the system or from equipment

completely removed and external to the system. Conversely, cables

can radiate the signal they are carrying into adjacent circuits (cross-

talk), generating interference to other data systems or causing se-

curity compromises in classified military communications. This

problem can be further compounded by poor cable-to-equipment

impedance matching which produces signal reflections and high

standing wave ratios. Poorly selected and installed cabling can act

as both transmitting and receiving antenna or as undesired primary

and secondary windings of coupling transformers, placing inter-

ference into the system.

PL75-9 Datasheet(PDF) 86 Page - List of Unclassifed Manufacturers

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