What is dual tone multi frequency, Electrical Engineering

Assignment Help:

Q What is Dual Tone Multi Frequency?

Dual Tone Multi Frequency (DTMF) was first introduced in 1963 with 10 buttons in Western Electric 1500 -type telephones. DTMF was originally known as Touchtone. DTMF is a more efficient means than dial pulsing for transferring telephone numbers from a subscriber's location to central office switching machine.

DTMF is a simple two-of -eight encoding scheme where every digit is represented by linear addition of two frequencies. DTMF is strictly for signalling between a subscriber's location and the nearest telephone office or message switching centre. DTMF is many times confused with another two-tone signalling system known as multi frequency signalling (Mf) that is a two-of-six code designed to be used only to convey information between two electronic switching machines. Figuredemonstrates four-row-by-four column keypad matrix used with a DTMF keypad. As the figure demonstrates, keypad is comprised of 16 keys and eight frequencies. Most household telephones, though, aren't equipped with special-purpose keys located in fourth column (which implies A, B, C, and D keys). Thus most household telephones actually use two-of-seven tone encoding scheme. Four vertical frequencies (known as low group frequencies) are 697 Hz, 852 Hz, and 941 Hz and four horizontal frequencies (called high group frequencies) are 1209 Hz, 1336 Hz,1477 Hz, and 1633 Hz. Frequency tolerance of the oscillators is + .5%. As demonstrated in Figure, digits 2 through 9 canalso be used to represent 24 of the 26 letters (Q and Z are omitted). Letters were originally used to identify one local telephone exchange from another.


Related Discussions:- What is dual tone multi frequency

Explain memory mapped i/o scheme, Explain Memory Mapped I/O Scheme. Me...

Explain Memory Mapped I/O Scheme. Memory Mapped I/O Scheme: In such scheme there is only one address space. These address space is defined as all possible addresses which m

Explain relative data addressing mode, Explain relative data addressing mod...

Explain relative data addressing mode (with examples) available in microprocessors. Relative Mode: Operand supplied is an offset, not the actual address. Added the con

Integrator with positive voltage on a noninverting input, Q. An integrator ...

Q. An integrator with positive voltage on a noninverting input is shown in Figure. Sketch v o for 60 ms after S has been opened.

Motor control , Normal 0 false false false EN-IN X-NO...

Normal 0 false false false EN-IN X-NONE X-NONE MOTOR CONTROL

How speech is transmitted in digital switching environment, Q. How speech i...

Q. How speech is transmitted in digital switching environment by using PCM/TDM? Ans: A digital carrier system is a communications system which uses digital pulses instead of

Armature winding, what is use of dummy coil in DC m/c????

what is use of dummy coil in DC m/c????

Non inverting summing amplifier, Q. In the non inverting summing amplifier ...

Q. In the non inverting summing amplifier of Figure, let R d = 1k and M = 6. Find R f so that v =

Check Sheets - Quality Tools for Improvement, Check Sheets - Quality Tools ...

Check Sheets - Quality Tools for Improvement This might be an easy listing of items that could represent information in an efficient, graphical format. If the system under ana

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd