Chapter 7 Tutorial
System Cabling and Connections
• Cable Resistance – Varies with wire gauge size and cable length. Use
the largest gauge wire possible and try to keep the cable lengths as
short as possible to minimize the cable resistance. The following table
lists typical cable resistance for copper wire of several gauge sizes
(the temperature coefficient for copper wire is 0.35% per °C).
ft (2 conductors)
AWG
at 25 °C
14
5 m
16
10 m
18
15 m
20 *
20 m
22
30 m
24
50 m
* Recommended wire size for the screw terminals on 34970A/34972A plug-in
modules.
• Cable Capacitance – Varies with the insulation type, cable length,
and cable shielding. Cables should be kept as short as possible to
minimize cable capacitance. In some cases, low-capacitance cable can
be used.
The table below lists typical cable specifications.
Cable Type
Nominal Impedance
Twisted Pair
100 at 1 MHz
Shielded Twisted Pair
at 1 MHz
Coaxial
50or 75 at 100 MHz
Twisted Pair Ribbon
100 at 1 MHz
258
Capacitance
Attenuation
10 to 20 pF/ft
Up to 1 dB/100 ft at 1 MHz
10 to 20 pF/ft
Up to 1 dB/100 ft at 1 MHz
15 to 25 pF/ft
Up to 6 dB/100 ft at 100 MHz
15 to 20 pF/ft
Up to 1 dB/100 ft at 1 MHz