Company newsGuides To Custom Cable

1. ATTENUATION – Attenuation is loss of power or signal expressed in decibels; it is commonly written and spoken of as dB/100 ft. at a specific frequency. An example is RG 8A/U which has a loss of 5.5 dB/100 ft. at 400 MHz.

2. FREQUENCY – Frequency is the term designating the number of reverses or cycles in the flow of alternating current (AC) in one second. For example, the frequency of AC commonly used in the U.S. is 60 hertz and is usually shown as 60 Hz. Broadcast stations operate at frequencies of thousands of cycles per second and their frequencies are called kilohertz (kHz). Your AM radio dial represents frequencies in kilohertz (kHz). High frequencies are in millions of cycles per second and are called megahertz (MHz). TV is broadcast in the MHz range.

3. IMPEDANCE – Impedance is a term expressing the ratio of voltage to current in a cable of infinite length. In the case of coaxial cables, impedance is expressed in terms of “ohms impedance”.The coaxial cables generally fall into three main classes; 50 ohms, 75 ohms, and 95 ohms.

An example of each class is:

RG 8A/U 50 ohms impedance
RG 11A/U 75 ohms impedance
RG 22B/U 95 ohms impedance

4. CAPACITANCE (CAPACITY) – Capacitance or capacity is the property of a system of conductors and dielectrics which permits the storage of electricity when a potential or voltage difference exists between the two conductors. A capacity value is expressed in farads.When we deal with coaxial cable, the capacity ranges we have are very small and are expressed in picofarads (pF)

Capacity is the major factor governing impedance. Examples of cables with typical impedances have capacity as follows:

RG or M17

Cable Impedance (ohms)

Dielectric Type

Capacitance (pF/ft)

RG 8A/U

50

PE

29.5

RG 231A/U

50

Foam PE

25.0

RG 188A/U

50

Solid TFE

29.0

M17/6

75

PE

20.6

RG 306A/U

75

FoamPE

16.5

RG 140

75

Solid TFE

21.0

M17/90

93

Air space PE

13.5

M17/56

95

PE

17.0

M17/95

95

Solid TFE

15.4

RG 24A/U

125

PE

12.0

RG 114A/U

185

Air space PE

6.5

5. VELOCITY OF PROPAGATION – Velocity of propagation, commonly called velocity, is the ratio of the speed of the flow of an electric current in an insulated cable to the speed of light. All insulated cables have this ratio and it is expressed in a percent- age. In the case of coaxial cables with polyethylene dielectric, this ratio is in the range of 65% – 66%.

In selecting coaxial cable, we must carefully consider not only design criteria, but use and application. Selection of materials in relation to overall design considerations is tabulated in folowing tables

INNER CONDUCTORS

INNER CONDUCTORS
SOFT BARE
COPPER
TINNED SOFT
COPPER
SILVER – PLATED
COPPER
NICKEL – PLATED
COPPER
TINNED – CADIMUM
BRONZE
COPPER
WELD®
Maximum operating temperature °C 200 150 200 250 150 200
Resistivity at 20°C,ohms – circular mil / ft. 10.371 11.133 10.371 12.5 11.92 25.928
Average tensile strength psi (1,000) 37 37 37.5 37.5 45 130
Flexibility excellent excellent excellent excellent good good
Remarks most popular – for extra flexibility use stranded for added resistance to oxidation and easy solderability, best for low frequency application elevated temperature usein aircraft, missile, and electronics, easy solderability extra high temperature use high tensilestrength with flexibility extra high tensile strength

Table1-Inner Conductors

INNER CONDUCTORS
SOFT BARE
COPPER
TINNED SOFT
COPPER
SILVER – PLATED
COPPER
ALUMINUM TUBE COPPER TUBE
Maximum operating temperature °C 200 150 200
Flexibility excellent excellent excellent poor poor
Remarks most popular in braid, minimum .004″ to .010″, add second shield to improve flexibility most popular in braid, minimum .004″ to .010″, add second shield to improve flexibility, better for low frequency most popular in braid, minimum .004″ to .010″, add second shield to improve flexibility, for high temperature for high tensile and crushing loads and lower attenuation for high tensile strength and crushing loads

Table2-Outer Jackets

Primary Dielectrics
POLYETHYLENE (PE) FOAMED POLYETHYLENE (PE) Fluorinated Ethylene Propylene (FEP) Poly Tetrafluoroethylene (PTFE) BUTYL RUBBER
Maximum operating temperature °C -65 to 80 -65 to 80 -65 to 200 -65 to 260 -40 to 80
Average tensile strength psi (1,000) 1.9 2.2 3.6 2.7 1.1
Flexibility good good excellent good excellent
Cut-thru resistance good poor good fair excellent
Water Resistance excellent poor excellent excellent good
Resistance to organic solvents poor poor excellent excellent good
Resistance to acids and alkalies excellent excellent excellent excellent good
Remarks for use under 80°C maximum for use under 80°C maximum for high temperature use to 200°C for high temperature use to 260°C for pulse cables and extreme flexibility

Table 3 – Primary Dielectrics

                                                                                                              JACKETS
POLYETHYLENE Tetrafluoroe-
thylene
(TFE)
Fluorinated Ethylene
Propylene (FEP)
PVC NEOPRENE® GLASS BRAID
Maximum operating
temperature °C
80 260 200 105 90 260
Average tensile strength
psi (1,000)
1.9 3.5 2.7 2.5 3.2
Flexibility good good good good excellent excellent
Resistance to organic
solvents
poor excellent excellent poor good excellent
Resistance to acids and
alkalies
excellent excellent excellent fair good excellent
Abrasion resistance good excellent excellent good excellent poor
Flame resistance slow burn nonflammable nonflammable self-extinguishing self-extinguishing nonflammable
Remarks for added resistance
to weathering
to mate with high
temperature dielectric
to mate with high
temperature dielectric
most widely used to mate with Butyl
dielectric
to mate with high
temperature dielectric