I was a teenager in the 90s, so I was on the phone constantly. Sometimes I could hear someone else’s phone call on my phone while I was talking to someone.
Sometimes they could hear it too, sometimes not. And I do recall this happening to my friends sometimes as well.
And how often could someone else hear my conversation?
In: Engineering
Imagine you have a really long plastic hollow pipe. You can talk through it and someone from the other side will be able to hear you even though you can be far enough that normal yelling wouldn’t reach. That’s what a phone line basically does.
In order to connect to multiple houses, you need multiple long pipes to each house. So you arrange the hollow pipes next to each other. But now, when you talk in one pipe, sometimes your voice reverberates into the other pipes and those listening in other pipes can also hear you.
This is called crosstalk. Where the electric field in the copper wires reacts to the wiring next to it causing the neighboring cables to also conduct the electric field. Telephone poles can hold hundreds of wires bundled together. So crosstalk was fairly common until it was cheap enough to change to twisted wiring that mitigated crosstalk. Not all wires have been upgraded though. But most have since back when dial-up was the primary form of internet for most people, you needed upgraded lines to be able to function at scale.
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