How to read catalog data - electrical characteristics

With regard to electrical characteristic of a cable, necessary parameter changes at low frequency and high frequency.

Low Frequency (Length of cable is short compared to signal wavelength)
- Direct Current Resistance (heat loss of its conductor is determined)
- Capacitance (storable quantity of electrostatic energy is determined)
- Dielectric Power Factor (heat loss of dielectric is determined)
- Insulation Resistance (direct current resistance of insulation)
- Inductance (storable quantity of magnetic energy is determined)
High Frequency (Length of cable is long compared to signal wavelength)
- Characteristic Impendance (reflectance of electromagnetic wave is determined)
- Velocity Ratio (propagation velocity of electromagnetic wave is determined)
- Attenuation Constant (heat loss of electromagnetic wave inside cable is determined)

Difference (borderline) between low frequency and high frequency for a cable is determined if reflection of transmitted electromagnetic wave matters or not. If it does not matter it is low frequency, and if it does it is high frequency. This borderline lies in the cable length that is about 1/10 of transmitted electromagnetic wavelength. The reason why reflection of electromagnetic wave does not matter at low frequency lies in that affection by reflection is fainted (fade out) while signal does not change almost at all.

When it is looked at from cable side,

  Cable Length / Transmitted Electromagnetic Wavelength << 1: Low Freuquency
  Cable Length / Transmitted Electromagnetic Wavelength >> 1: High Freuquency

Never forget this, as it is not determined by extent of frequency. In case signal waveform is other than sine wave, it is compared with the highest frequency component (spectrum) wavelength.

Wavelength of electromagnetic wave is given by following equation.

  λ = Vp / f
  hereby,
	λ = wavelength of electromagnetic wave (m)
	Vp = phase velocity of electromagnetic wave (m/s)
	f = frequency of electromagnetic wave (Hz)

Phase velocity of high frequency is calculated by following equation.

  Vp = c * Vr
  hereby,
	c = light velocity in vacuum (299,792,458 m/s)
	Vr = velocity ratio of cable (0 < Vr <= 1)
	   = 1 / sqrt(εs)
	εs = (equivalent) relative permittivity of cable dielectric (1 <= εs)

Relative permittivity of polyethylene is about 2.3, therefore velocity ratio of polyethylene insulated coaxial cable at high frequency is about 0.66. Velocity ratio at low frequency range becomes smaller than that at high frequency range.

Electrical characteristic at low frequency is called primary parameters in transmission line theory and that at high frequency is called secondary parameters.

As far as energy transmission is concerned, above characteristic factors are enough, however, there are cases that the following characteristic must be considered depending on applications.

Microphonics - phenomenon that cable itself becomes a generator by mechanical vibration
Shielding effectiveness - Countermeasure against electromagnetic coupling with other circuit

Microphonics is a noise caused by static electricity generated by mechanical vibration, etc., it becomes problem when a cable is used at high impedance circuit.

Shielding effectiveness involves all of different physical mechanism countermeasure against Conductive Coupling (Common Impedance Coupling), Electromagnetic Coupling (Mutual Inductance Couplig), Capacitive Coupling (Mutual Capacitance Coupling) and Electromagnetic Wave Coupling (Radiation Field Coupling), therefore special care is required. Namely, this word itself is obscure.