# What are the frequencies of current in computers' external peripheral cables and internal buses?

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!

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I can tell you that the PSU is an ACDC adaptor – barlop Aug 28 '12 at 15:25
@barlop: do you mean the currents in computers' external peripheral cables, such as Ethernet cable, USB cable, and in computers' internal buses are all DC, so their frequencies are all zero? – Tim Aug 28 '12 at 15:28
@Tim - Go Test It Out :-) – Ramhound Aug 28 '12 at 15:36
@Tim I suppose they'd all be DC. 0 freq. USB is 5V DC generated from the port, USB has 4 wires, 2 for data and 2 for power, a + and GND. Internal buses are DC(because of the PSU) but I don't know about the volts. Ethernet I don't know. Ethernet as far as I know doesn't have any power wires like + or GND, but according to this yahoo link has about 2.5V I would guess DC as ones i've seen haven't connected to any AC source. answers.yahoo.com/question/index?qid=20080817012235AAkgJXB And i'm sure the only thing in a computer taking AC In, is the PSU. – barlop Aug 28 '12 at 15:37
@barlop: in data wires of USB cables, and ethernet, all that are transmitted are electrical currents, right? – Tim Aug 28 '12 at 15:41

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?

This information should be available in either the appropriate Wikipedia articles or in the relevant technical standards (which are probably referred to in those articles)

In general the signalling rate or frequency is not the same as the data rate (due to encoding, the use of multiple transmission channels (e.g. pairs) and other factors) but dividing by ten will give you a (very) rough idea.

For example, 1000Base-T Ethernet has a data rate of 10^9 bits/second, so you could assume a signalling frequency that is 100 MHz.

For the actual rate, use Google (which would lead you to relevant articles)

Are the cables also made specially for the frequencies?

Yes.

Sometimes the data transmission standards are made to match an existing cable specification. For example, I believe the original 10Base-T spec was designed so people could use existing premises wiring standards that had been designed for voice telephony not for Ethernet. This reduced the cost of deploying 10Base-T and may (in a small way) have helped sales of Ethernet products.

Update:

If you want a rigorous answer, be careful about using vague terms like electricity.

Note that (so far as I know) most electrical signalling systems used with computer peripherals nowadays look at voltage changes at specific frequencies, they don't look at current (c.f. current-loop interface). So it isn't useful to think of "current frequency".

Note: I am not an electronic engineer.

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No that's bits per second. Totally the wrong layer. He's asking about the electricity. Not the bits. Electricity is lower level than bits. – barlop Aug 28 '12 at 15:45
What is the difference between "signal frequency" and electricity frequency? – Tim Aug 28 '12 at 15:47
@Tim all I can say there is frequency is a thing per second. Measured in Hz which is a unit for things per second. – barlop Aug 28 '12 at 15:49
@barlop: isn't that what I said in my second paragraph (it's what I meant) – RedGrittyBrick Aug 28 '12 at 15:50
@barlop: I got some nice answers here electronics.stackexchange.com/questions/38989/… – Tim Sep 4 '12 at 13:41