Crosstalk in transmission
How a signal leaks into a neighbouring wire, corrupts data, and how twisted pairs and shielding fix it.
Transcript
Crosstalk happens when a signal on one wire leaks into a wire right next to it.
A changing current creates a changing magnetic field, and that field induces a faint copy of the signal in the neighbour.
The neighbouring wire should be idle, but the receiver sees small spikes every time the first signal changes.
If a spike is big enough, the receiver reads a zero as a one, and the data is corrupted.
Crosstalk gets worse with longer cables, higher frequencies, and wires that sit closer together.
Twisting each pair of wires makes the interference hit both wires equally, so it cancels out.
Shielding wraps the wires in metal, which blocks interference from getting in or out.
Short, well separated cables help too. Ethernet cables use all of these tricks.
Crosstalk is unwanted signal leaking between wires. Twisting and shielding keep it down.
More in this series
1:32Data packets and packet switching
Packet structure, routing, out-of-order arrival and reassembly.
1:19Simplex, half-duplex and full-duplex
Which way the data flows, and when.
1:43Serial and parallel transmission
Bits one by one or all at once, skew, crosstalk and USB.
1:21Error detection
Why errors happen, and checksums, echo checks and ARQ.
1:13Parity checks
Parity bits and parity blocks, including finding and fixing a flipped bit.
1:32Check digits
The multiply, add, divide-by-10 method with a worked example and a practice question.
1:28Encryption
Eavesdroppers, symmetric keys and the public and private key pair.
5:08Unit 2 quiz
Ten questions with a think-time countdown and explained answers.
1:48When to use serial or parallel
Choosing between serial and parallel: inside a computer, computer to printer, USB, Ethernet and a distance rule of thumb.