How do cable lines on telephone poles transmit and receive data along thousands of houses and not get interference?
In: Engineering
The analog signal from connection point to your house is not very long. And it actually not uncommon to get some powerline interference (50 or 60 Hz hum).
From the connection point to the core network it will be digital and not susceptible to interference in the same way.
It’s similar to how AM and FM radio work. When your analog audio signal from your phone is modulated onto another signal you can fit millions of different audio signals.
From what I remember (which may be not completely correct), when you’re dialing a number, you’re setting switches along a route to the destination number, and the phone provider sorts incoming traffic to the proper destination.
They do get interference. Look up ingress and egress for cable. The FCC is very strict about this and signal leaks are almost immediately taken care of
Eli5 answer: There is interference. But the content can be transformed into a format that is easier to send. Additionally the sent signal is processed to minimize the impact of the interference.
The answer is: they do.
That’s what phone calls have noise and why data needs error correction.
Cable tech here that works in a HFC (Hybrid Fiber-Coaxial System) system. The radio carriers are used in many different ways in many different systems, one common one is (in a very simplified way) timing the signal transmissions of equipment back to the server with each other so they dont overlap. A common system as well is equipment being assigned different portions of the radio frequency spectrum so they dont overlap with each other (except in minimal ways as to minimize it). The two most important things cable techs keep in mind for a clean and working system, is to minimize outside interference because most RF networks like cable systems overlap with cell carriers over-the-air as well as other RF sources like other over-the-air tv and communications, so we must maintain a closed and sealed system, this means no damaged lines, no open connections, and most importantly customers who try to do things themselves use terrible quality coax or connectors which allow outside RD carriers to bleed into our system which interrupts services as they can and will overlap. Sorry for terrible English, busy while answering but saw my opportunity! Cant focus on the grammar.
Edit: grammar
They do!
Interference is a big issue. When I was in cable TV, I’d disconnected numerous homes for causing interference in the rest of the plant. Leaving a note saying why, and for them to schedule an appointment to see if we could track it down.
Damaged coax, poor connectors, and even some TV have been the culprit in most cases.
It can also get in from the plant side.
If you’ve ever noticed several small antennas on your cable providers vehicles, those are connected to ~~socialized~~ *specialized* receivers known as “leak detectors” and look for a specific frequency.
My old company used a computerized system that collated all the detected transmissions, and used GPS and triangulation to determine exactly where it was coming from. Usually from animal chew, or other types of damage to the physical lines.
Squirrels apparently love the “white shit” aka dielectric, inside them…
They can’t. Nowadays most are converted to digital (or a series of ones and zeros that represent the analog signal), and these signals are transmitted. When they get close to where they want to go, and the result of the interference would be small, they’re converted back to analog.
As /u/doyouseeit suggests, older lines would multiplex the signals together. Think of it like the radio in your car. The signals from each station are separated, and interference will be minimal. There is still interference, but it could be minimal with large separation between the signals. (Note this also implies an expensive wire to transmit the data that could give you enough separation between the signals.)
There is a whole branch of mathematics related to this, called communication theory. It was really established when a smart man called Claude Shannon took work started by Harry Nyquist and really proved a lot of unexpected things. Although that work was originally complicated, many cases of the math have largely been solved to a degree that you can take off-the-shelf solutions, and guarantee communication to whatever reliability standard you want.
The data is converted into digital, electromagnetic waves. The data is then converted from time domain into what is called frequency domain. Filters can be applied to single out individual frequencies to “find” the correct information you want to look for.
Think of a radio. When you turn the dial on the radio it changes the stations. Each one of these stations, on FM, are on different frequencies. Turning the dial essentially filters out each station and finds the one you want to listen to. All of these stations are still being transmitted layered on top of one another. Digital data over cable lines and telephone lines can have thousands of available “stations” instead of the handful you can hear from FM radio. When you filter out the frequency you want, it also removes the “interference” of other frequencies.
Electrical Engineer here.
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