How do cable lines on telephone poles transmit and receive data along thousands of houses and not get interference?
In: Engineering
EDITED AFTER POSTING BUT I’M NOT GONNA EDIT MORE TO REMOVE REDUNDANCIES.
Big picture.
Analog computer modems were using digital info compressed into an audio signal that sounded like hissing static sounds.
Phone signals and internet over phone lines using an old analog modem connected to your telephone line, that’s highly compressed analog information – high pitched sound like what you could hear when the modem first connects, or if you pick up the phone and listen when someone was logged in to AOL.
The sound you hear is two modems “singing” data to each other.
Phone lines carry not only compressed voice but also could carry that “conversation” of computer data with the internet service provider using that same basic analog signal. So, text and pictures digitized but then converted to sound.
Modems were listed at 14k/sec then 28k 33k and 56k, but I think the max actual transmission speed was 28.8k/sec plus super compression (like WinZip files) for 56k.
Then DSL came around, a digital signal running at a frequency high above all phone audio. So I think DSL is still “somewhat audio” but totally different from phone audio and modem audio.
Analog modem was one call at a time. You have to hang up the phone to login online, and log off the internet to make a phone call.
DSL can slide in side by side with regular analog phone calls.
VOIP is phone voice that is digitized and flowing as DSL data, the opposite of data flowing as analog signal.
Over the air TV also compressed video and audio into a radio wave that is decoded by the TV tuner into human level information.
Cable transmits digitized voice, digitized video, and digitized audio (plus computer data) over cable. Connections are established and packets that are communicated are addressed to their destination. THERE’S NOTHING ANALOG ABOUT CABLE SIGNALS until the receiver decodes it.
So your home cable signal is kinda like personal point-to-point, because of digital addressing, but all together within a stream, but with digital addressing to separate signals from your neighbor’s point to point connection. (Not audio multiplex.)
You can SEE the difference. When a discrete digital TV signal gets stopped or corrupted, you see missing square chunks or a frozen screen or blank.
When an analog signal is imperfect you see and hear increasing levels of static speckling and may see bleed-through as the tuner tries to decode two nearby signal frequencies, tuning in on one and tuning our others, but not being very successful.
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