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

Cro, Diagram and explanation of cro

Diagram and explanation of cro

What would the cutoff frequency, Q. The cutoff frequency of a dominant mode...

Q. The cutoff frequency of a dominant mode in an air-?lled rectangular waveguide is 3 GHz. What would the cutoff frequency be if the same wave - guide were ?lled with a lossless di

Find the charge flowing and the number of electrons, Q. A current i(t) = 20...

Q. A current i(t) = 20 cos(2π × 60)t A fows through a wire. Find the charge flowing, and the number of electrons per second that are passing some point in the wire.

Bode plot phase ad gain margin, Using Bode plot calculate (a) Phase margin ...

Using Bode plot calculate (a) Phase margin (b) Gain margin (c) Stability of closed loop system. The open transfer function of the system is t=30/(s+2)/(s+3)Using Bode plot calcula

#title., what is plane transmission grating/?

what is plane transmission grating/?

8 bit data to register - move immediate instruction , 8 bit  data to Regi...

8 bit  data to Register   This form  of the  instruction is used to copy 8 bit  data directly  to the register  location specified in  the instruction. The  instruction format i

Asset information management system, Asset information management system: ...

Asset information management system: GIS has the potential to revolutionize the reform procedure in areas such as consumer indexing, asset and work management, distribution ne

What is direct memory access, What is Direct memory access? Direct memo...

What is Direct memory access? Direct memory access (DMA) is a process wherein an external device takes over the control of system bus by the CPU.DMA is for high-speed data tran

Obtain the complete solution for the voltage, Consider the circuit of Figur...

Consider the circuit of Figure and obtain the complete solution for the voltage v C (t) across the 5-F capacitor and the voltage vx(t) across the 5- resistor.

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