PL75-9 datasheet(85/141 Pages) ETC

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Electronic systems wiring & cable

Many cable defects are not readily visible and may not show up with-

out proper testing. The reputation of the manufacturer, the type, quan-

tity and quality of material used is more important than cost savings

in selecting coax cable.

Be careful that cable does not support heavy equipment or is subject

to prolonged exposure to heat in system installations. Do not bend

cable beyond the manufacturer's recommended bend radius in order

to avoid producing cable discontinuity. Try to space high signal level

or power circuits separate from low signal level cables when routing

cables.

Signal cables are usually manufactured with polyethylene which is

adequate for normal use. Teflon™ dielectric and sheathed cables

should be used where high heat or chemical action will attack poly

cables (such as in aircraft or industrial plants). The National Fire Un-

derwriters now requires non-fire supporting cable to be used for all

open wiring in public buildings (plenum wiring). Fire insurance rates

can be greatly reduced in computer, nuclear accelerator and other large

installations if TFE or FEP cables are used.

All transmission cable manufacturers should provide the electronic

characteristics of their cables (including power handling and attenua-

tion per foot versus frequency) to aid the system design engineer in

doing a proper job. For instance, RG58C has the following character-

istics if built to military specifications:

Attenuation in dB per 100 foot length

(Ambient temperature 100°F in free space at sea level)

Frequency MHz

100 200 400

Attenuation

3.3

4.9

7.4

Power (Watts)

450 300 200 135

Note how quickly the cable becomes unusable at the higher frequen-

cies. Lowering the dielectric constant of the dielectric with Teflon™

or foamed Teflon™ and silver plating the inner and outer conductors

to increase the skin effect conductivity will greatly improve the high

frequency usage. The increase in performance justifies the additional

cost. Keep in mind that for a 10 dB loss, only 3/10ths of the transmit-

ted voltage will show up at the receiving end, and only 1/10th of the

generated power will be available. (Assuming a reasonably good im-

pedance match.) If the operating temperature is higher than the rated

temperature or if the cable is used at high altitudes, the attenuation

and power handling capacity should be derated.

Low-priced cable should be carefully considered. Any reduction in

the amount of copper in the conductors or in the quality of materials

used throughout will effect performance. Many manufacturers pro-

vide better performance in their smaller cables by using materials

better than minimum Mil Specs require. Cable performance will also

degrade with time and can be adversely affected by the environment

where it is installed (sun, ozone, salt, sulphur products, etc.). A cable's

shielding effectiveness versus the signal frequency to be transmitted

should also be considered where noise pickup can be a problem. It is

usually financially and physically impossible to undo any damage or

replace cables once they are installed and terminated.

All RG59 cables are not the same. By adding the word “Type” a

manufacturer may bypass minimum spec requirements to reduce pric-

ing. Some manufacturers build a "better than Mil Spec" cable and

supply a superior product. They also must use the word “Type” since

they exceed or deviate enough from the electrical and mechanical

specifications. (This also applies to connectors). Be cautious of "low

bid" surplus dealers, distributors, or packaging houses. Inventoried

cable may deteriorate with time. The design engineer and installa-

tion technician must be aware of the many hidden and unknown cable

properties that may be detrimental to the system's performance. Buy-

ers accepting low bids may burden engineers and technicians with

future problems due to hidden deficiencies.

Coax Cable Connectors

Any connector must be able to interconnect with very low DC series

resistance (less than 10 milliohms). The impedance of a connector

is usually of no consequence below approximately 300 MHz. The

connector does not contribute to circuit performance until the signal

length approaches 1/20th of a wavelength. 50 ohm connectors can

be attached to 75 ohm video cables with little detrimental effect.

However, the effect of a connector on a signal is cumulative. Coax

connectors should be impedance matched to the system impedance

for frequencies above 300 MHz.

The generation of intermodulation and nonlinear distortion caused

by the presence of ferromagnetic material in the conductor has be-

come a more prominent factor in the selection of cables and connec-

tors.

Heat treated beryllium-copper should be used for critical con-

tact springs to maintain contact resilience. Many manufacturers use

ordinary brass which soon loses its contact pressure and the connec-

tor becomes noisy or fails.

The systems engineer can no longer afford to take connectors for

granted. He must be aware of cable characteristics such as attenua-

tion, phase displacement, and transfer impedance. The systems en-

gineer must also understand the inherent characteristics of the many

connector families available and the strengths and weaknesses of

individual manufacturers' connector designs. He must be willing to

expend the time and effort to specify the quality component his sys-

tem demands.

The many types and series of coax connectors presently available

can cause confusion for users. Many of the lesser known series were

designed to address specific problems or were developed by com-

mercial companies for their own proprietary product line. The con-

nector series listed below have gained universal acceptance due to

their simplicity and performance. They are produced and stocked by

the majority of coax connector manufacturers.

Nominal Cable

Connector

Quick

Threaded

Size O.D.

Size

Disconnect

.060 to .425

Standard

.060 to .425

Miniature

BNC

TNC

.060 to .225

Subminiature

TPS

TCM

Much can be written to discuss the advantages of one series of con-

nectors over another. Selection is normally based on cost or perform-

ance depending upon the system parameters required.

PL75-9 Datasheet(PDF) 85 Page - List of Unclassifed Manufacturers

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