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I am having a doubt about waveguides and the traditional Ethernet cable.

The newest Ethernet i.e. the 10Gbps Ethernet has an astounding speed of 10Gbps. Which consists of 4 lanes in Cu as physical media. Each wire pair carries 3.125 G baud as signal!

Now that's enormous even for Cu cable.

Does that somehow violate the waveguide principle, that the impedance of the carrier should be lesser than the impedance of the environment, and as the freq. of wave increases the impedance of carrier increases...

Some light in this might be helpful...

Regards Vineet

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Isn't 10 gig ethernet transmitted over fiver optic lines? – Colin K Aug 11 '11 at 7:18
der are physical layer available in Cu variants too... en.wikipedia.org/wiki/10_Gigabit_Ethernet#Copper – Vineet Menon Aug 11 '11 at 7:21

2 Answers

up vote 4 down vote accepted

Copper conducts to extremely high frequencies. What you're probably thinking about is "skin effect" which does depend on frequency.

As frequencies become higher and higher, the current-carrying thickness in a conductor decreases. This means that the resistance of a copper wire depends on the frequency. As you note, very high frequencies imply that this resistance is raised.

But as far as sending signals down a wire, the only problem with high resistance is that, for the same voltage, one must use less current.

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actually, I wanted to compare waveguide and conductors for signal transmission. That said, why isn't it that Cu while conducting doesn't radiate energy, is it because of the twisting in UTP?? because if that's the case then why not use UTP's in microwave instead of waveguide to transmit energy?? – Vineet Menon Aug 12 '11 at 8:41
Twisted pair works by arranging for the emissions (radiation) and absorptions (noise interference) of one wire to cancel the other. This happens when (a) you send and receive balanced or complementary signals down the wire, and (b) the minimum wavelength of the signal is longer than the twist. You could also do this at microwave frequencies, depending on the wavelength and your ability to twist the conductors. Microwave frequencies are say 300MHz to 300GHz. The usual twisted pair could be useful for 300MHz to around 5 GHz. – Carl Brannen Aug 12 '11 at 17:28
but even thought as u say UTPs could be used for microwave transmission, still its not used even though its a much cheaper alternative....My guess would be that there is something we are missing...2.42GHz for microwave oven.. – Vineet Menon Aug 13 '11 at 6:08
Suppose you lose 50% of your power in transmitting a digital signal down a UTP due to resistance effects. This is not a problem so long as the receiver is able to receive the signal. But if you lose 50% of your power in transmitting 1KW to a frozen dinner, this is a problem as it will melt your microwave oven. So it's a matter of efficiency that relates to the power levels and the design objectives. – Carl Brannen Aug 15 '11 at 0:20
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1000BaseT and 10GBaseT both use amplitude modulation so that a cable with a maximum frequency of 500Mhz (cat6) can carry much higher amounts of data.

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