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Friday, March 31, 2017
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   Calculate Cable Length & High Frequency Loss


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  • at which cutoff frequency fc the interconnect cable has a -3 dB loss of treble (Treble frequencies are attenuated)?
  • Which length [ d ] a cable can have to reach this damping?
  • How are high frequencies damped by the length of the cable?

Cables are characterized by the capacity of the cable between the conductors, the resistance, inductance of the cable along the conductor, and the current crowding, which boost the resistance at high frequencies.

The most interlinks cable usually have a capacitance from wire to wire of about Cspec = 100 pF per meter.

The line resistance, and the inductance is usually negligible in practice. Each wire has an unavoidable cable capacitance, that leads to the damping of high frequencies (cable loss). Because the input resistance (load) is large against the small source output impedance, the input impedance (load) can mostly be neglected.






 Source impedance [Zout  ohm
Capacitance [C] per m   pF/m
Cable length [d]  meters 
Attenuation [Att]  dB
Cutoff frequency [fc  Hz
 
Zout = Output impedance of the source impedance ( Pre Amp )
Cspec = Specific capacitance of the cable in pF per m cable lenghth

d = Length of the cable in meters

C = Cspec x d

 
Formula for the cutoff frequency of the treble damping:

Cable cutoff frequency


  • How long can the cable be, without having too much treble loss?


  •  Source impedance [Zout  ohm
    Capacitance [C] per m   pF/m
    Attenuation [Att]  dB
    Cutoff frequency fc   Hz
    Cable length [d]   meters 
    Formula for the length of the cable d and a given cutoff frequency fc:

    Cable length

    fc = Cutoff frequency at -3 dB treble loss
    Zout = Output impedance of the source impedance ( Pre Amp )
    Cspec = Capacitance in pF per m cable lenghth C = Cspec x d



        Cable Calculator



    Cable Length [m] : Diameter : Conductor :
     
    Impedance of a single wire cable : Ohms Impedance of a twin wire cable : Ohms