What are the frequencies of current in computers' external peripheral cables and internal buses?
- by Tim
From Wikipedia, three different cases of current frequency are discussed along with the types of cables that are suitable for them:
An Extra Ordinary electrical cables suffice to carry low
frequency AC, such as mains power, which reverses direction 100 to
120 times per second (cycling 50 to 60 times per second).
However, they cannot be used to carry currents in the radio frequency
range or higher, which reverse direction millions to billions of times
per second, because the energy tends to radiate off the cable as radio
waves, causing power losses. Radio frequency currents also tend to
reflect from discontinuities in the cable such as connectors, and
travel back down the cable toward the source. These reflections act as
bottlenecks, preventing the power from reaching the destination.
Transmission lines use specialized construction such as precise conductor dimensions and spacing, and impedance matching, to carry
electromagnetic signals with minimal reflections and power losses.
Types of transmission line include ladder line, coaxial cable,
dielectric slabs, stripline, optical fiber, and waveguides. The higher
the frequency, the shorter are the waves in a transmission medium.
Transmission lines must be used when the frequency is high enough
that the wavelength of the waves begins to approach the length of the
cable used.
To conduct energy at frequencies above the radio range, such as
millimeter waves, infrared, and light, the waves become much smaller
than the dimensions of the structures used to guide them, so
transmission line techniques become inadequate and the methods of
optics are used.
I wonder what the frequencies are for the currents in computers' external peripheral cables, such as Ethernet cable, USB cable, and in computers' internal buses? Are the cables also made specially for the frequencies?
Thanks!
