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Talk-Talk, Talk Crap

Ezra Pound

Well-Known Member
#1
I couldn’t resist posting this explanation on the Talk-Talk website of their new Superfast Broad service, I am guessing it is VDSL or Fibre To The Cabinet, where there is a fibre link to a street cabinet and a copper wire link from there to your house. According to Talk-Talk photons travel at the speed of light BUT electrons travel at the speed of sound, including the ones from the cabinet to your house presumably

talk-talk-superfast2.jpg
 

Black Hole

May contain traces of nut
#3
Just in case anybody needs to be told: signals on copper wires DO NOT travel at the speed of sound, even though the average electron drift might be of that order*. Waves pass across a pond even though the actual water isn't going anywhere.

As an engineering rule-of-thumb: the speed of light is a foot per nanosecond, and signals in conductors depend on a variety of things but c/2 is a good starting point. Photons in a fibre also travel slower than c (the speed of light in a vacuum).

The advantage of data transmission by fibre is the bit rate that can be encoded on the photon stream compared with the bit rate that can be encoded in the bandwidth of a copper transmission line that may be several km in length, not the speed of travel of anything.

* I checked, and electron drift is typically measured in metres per hour, so no - nothing about any form of electrical signal in copper goes at the speed of sound!
 

fenlander

Active Member
#6
Time to stop drinking and go home when you can't tell whether or not the words are slurred (or how many syllables are in them).
 

Trev

The Dumb One
#7
Or to put it into words of one syllable (almost) you can’t modulate a carrier at a rate faster than the carrier
No you can't even do that sucessfully. Mr Nyquist said that the carrier has to be at least twice the modulating frequency.
And as this is the Hummy Arms. The use of the words 'rate faster' is not appropriate in this instance, it should be higher, as in (wrongly) 'at a higher frequency than the carrier ' ;=)

EDIT: Just realised that the word faster might just have been used deliberately, in view of TalkTalk's BullBullS***S***
 

Trev

The Dumb One
#10
@ Ezra. The comment was about modulation, not pointed at anyone. Perhaps I should have said 'No, even that can't be done successfully. Mr. Nyquist etc.' (Even spelled successfully right this time)
@ Wallace. I thought it was called trolling, although trolls seem to be getting a bit of a bad press lately, 'specially on FB I believe. I personally go along with the DNFTT principle. ;=)
@ BH. I'm certain that you really mean 300mm/nSec ;=). Ah, no, we are in GB which still uses miles and yards so a foot is OK
 
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