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Author Topic: DTMF
Akanksha
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Post DTMF
on: January 16, 2014, 07:38
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DTMF. Does it bleep your brain? Well not that its abbreviation wouldn’t! DTMF else called “Dual tone multi frequency signaling”. Hey! Am I hearing alien? Not really.
DTMF was used for telecommunication signalling over analog telephone lines. It was used in push button telephones when the trend started around world war two developed by the Western Electric and used by Bell systems .
DTMF technology turned out to be very important indeed. So how did it all start?
Retrace your memories. yes, and it all starts with telephone operators and trunk dialling that ended up like a nuclear chain reaction rapidly disconnecting and re-connecting the telephone lines resulting in a series of clicks and flickers and barely any steady human voice at all. Plus added problems of phone tapping getting into people’s private conversations. Hence pulse dialling or loop disconnect lead to chaos.
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And now comes DTMF to the rescue! This technology used 8 different frequency signals in pairs to represent 16 different numbers letters and characters.
The television broadcasters took up this in-band signalling later modified and developed as out-of-band signalling in the 90’s.
Well what were the super powers of our DTMF hero? It was speed and cost effectiveness. Dual-tone multi-frequency (DTMF) signaling was developed for the consumer to signal their own telephone-call's destination telephone number instead of talking to a telephone operator.
Its victory board read "a method for pushbutton signaling from customer stations using the voice transmission path."
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DTMF keypad was setup as shown that included vertical service codes and signs like “#” and “*”
These codes being used by public payphones through magnetic strips to the pentagon ,USA that used them for call diverting based on priority.
Present-day uses of the A, B, C and D keys on telephone networks are few, and exclusive to network control. For example, the A key is used on some networks to cycle through different carriers at will (thereby listening in on calls). Their use is probably prohibited by most carriers. The A, B, C and D tones are used in radio phone patch and repeater operations.
The *, #, A, B, C and D keys are still widely used worldwide by amateur radio operators for remote-base operations and telephone communications systems.
DTMF tones are also used by some cable television networks and radio networks to signal the local cable company/network station to insert a local advertisement or station identification.
DTMF signaling tones can also be heard at the start or end of some VHS (Video Home System) cassette tapes. The encoded tone provides information to automatic duplication machines, such as format, duration and volume levels, in order to replicate the original video as closely as possible.
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Thinking it’s an outdated system that will be lashed out few years down the lane? Well you’re wrong! DTMF is used in today’s tech-freak life too . It’s used to control autonomous bodies from a distance. Say maybe spy robots for military purposes or mechanical systems for surveillance in hard to reach places like a land slide, a building rubble and all this by using just your smartphone or any other ordinary phone for that matter. Isn’t it cool? A simple principle that goes on to do wonders.
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thomaswhit-
e544
Newbie
Posts: 10
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Post Re: DTMF
on: March 15, 2016, 09:18
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Nice and interesting article. You explained really well. Thank you so much for sharing.

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