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Coaxial Cabling

Coaxial cabling is the oldest and most venerable of transmission mediums. It has been in use since at least 1898, when Hertz made his original investigations of wave propagation on transmission lines. Despite its age, the electrical performance of coaxial cable is as good as anything else.

Physically, coax is a mess (see Chapter 7, "Generic Building-Cabling Standards"). The problem with coax is topological (Figure 10.1). To access the inner conductor, you must first peel back the outer jacket, outer shield, and inner dielectric. This error-prone procedure takes a long time in the field and often results in an unreliable connection. Pre-fabricated jumper cables made with good tools, under ideal manufacturing conditions, work just fine. Field-applied connectors don't. Coax connectors (compared to UTP) are extremely difficult to apply.

Figure 10.1. A coaxial cable has four parts .

graphics/10fig01.gif

Coaxial cable suffers from an overabundance of standards. To begin with, the mechanical properties of coaxial cable are controlled by a series of RG specifications. These specifications were written in the early sixties by the American military. The electrical properties in the RG specifications are very loosely specified. These specifications leave open many questions having to do with conductor construction, stranding, surface roughness, surface plating , use of steel cores, and dielectric material selection, all of which affect the electrical properties. Most modern cables rated for a particular RG class of operation will far outstrip the capabilities of that class. [84] If you want to know how a particular cable will perform, you have to examine the vendor's specifications for that type of cable.

[84] By as much as a factor of two.

From among all the thousands of variants available, I've selected a particular set of cables manufactured by Belden ( www.belden.com ) for all the examples in this chapter. The cables are listed in Table 10.1.

Table 10.1. Selected Belden Coaxial Cable Types

Belden cable type

Class

Jacket O.D. (in.)

Conductor stranding and gauge (AWG)

Conductor composition

Dielectric

8216

RG-174/U

0.110

7 x 34

Bare copper -plated steel

Polyethylene

84316

RG-316/U

0.098

7 x 33 ½

Copper-plated steel with silver coating

TFE Teflon

8259

RG-58A/U

0.193

19 x 32

Tinned copper

Polyethylene

8240

RG-58/U

0.193

20 Solid

Bare copper

Polyethylene

84303

RG-303/U

0.170

18 Solid

Copper-plated steel with silver coating

TFE Teflon

8237

RG-8/U

0.405

7 x 21

Bare copper

Polyethylene

POINTS TO REMEMBER

  • The electrical performance of coaxial cable is as good as anything else, but physically, coax is difficult to handle.
  • Coaxial cable suffers from an overabundance of standards.


Fundamentals

Transmission Line Parameters

Performance Regions

Frequency-Domain Modeling

Pcb (printed-circuit board) Traces

Differential Signaling

Generic Building-Cabling Standards

100-Ohm Balanced Twisted-Pair Cabling

150-Ohm STP-A Cabling

Coaxial Cabling

Fiber-Optic Cabling

Clock Distribution

Time-Domain Simulation Tools and Methods

Points to Remember

Appendix A. Building a Signal Integrity Department

Appendix B. Calculation of Loss Slope

Appendix C. Two-Port Analysis

Appendix D. Accuracy of Pi Model

Appendix E. erf( )

Notes

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High-Speed Signal Propagation[c] Advanced Black Magic
High-Speed Signal Propagation[c] Advanced Black Magic
ISBN: 013084408X
EAN: N/A
Year: 2005
Pages: 163
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