how data and power can be sent down the data lines of a poe connection

[amateur_25]

Hi

If it's a 100mbps connection then you can use the spare pairs to send power to your device then split it up at the device you're powering.

But Gigabit Ethernet use all 4 pairs so how can you send data and power at the same time without affecting the integrity of signal?

Also does these so call powerline device (ethernet connection over mains wiring) work in the same way

[Monkeh]

Hi

If it's a 100mbps connection then you can use the spare pairs to send power to your device then split it up at the device you're powering.

But Gigabit Ethernet use all 4 pairs so how can you send data and power at the same time without affecting the integrity of signal?

AC coupling.

Also does these so call powerline device (ethernet connection over mains wiring) work in the same way

In the broadest sense.

[amateur_25]

oh Ac coupling ah. So basically in newbie speak it the data signal is actually an ac signal.

By using capacitors it can then filter out the dc as if it's not there.

Then how do home plugs work because mains is AC.

Am guessing it knows the difference between whats ac power and the data because
mains electricity in the uk is 50hz and Ethernet has a higher frequency?
Similar to how broadband and voice are sent down the phone line yes?

[Monkeh]

Then how do home plugs work because mains is AC.

Am guessing it knows the difference between whats ac power and the data because
mains electricity in the uk is 50hz and Ethernet has a higher frequency?

Basically, yes. Just filter out the boring low frequency components.

Similar to how broadband and voice are sent down the phone line yes?

Actually, yes. It's very much like DSL.

[andtfoot]

By using capacitors it can then filter out the dc as if it's not there.

Close, but in this case it uses centre-tapped transformers (called magnetics) to split the signal from the power.

[kc8apf]

Ethernet uses transformer-coupled data lines on both ends.  Any DC offset present on the lines is thus removed before it hits the PHY.

I'm not up on the latest home powerline standards but there are a few different schemes.  As you've already noted, mains power uses AC but at a low frequency (50 or 60Hz).  A few of the schemes work by using a higher-frequency modulation scheme that essentially treats the house wiring as an RF connection.  Something like QAM1024 at a few hundred MHz will give a lot of data rate.  Older systems like X10 (I think it was X10), send high-frequency bursts during the mains-power zero crossing.  That makes the receiver simpler (no need to add downconvert) but significantly reduces the data rate as your 1MHz symbol rate can only happen for a few milliseconds per second.