Dual Tone Multi Frequency (DTMF)

From Signal Identification Wiki
Jump to: navigation, search
Dual Tone Multi Frequency (DTMF)
DTMF tones.png
Frequencies 30 MHzMegaHertz (MHz) 10^6 Hz30,000,000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
30,000 kHzKiloHertz (kHz) 10^3 Hz
,800 MHzMegaHertz (MHz) 10^6 Hz800,000,000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
800,000 kHzKiloHertz (kHz) 10^3 Hz
30,000 kHzKiloHertz (kHz) 10^3 Hz
30 MHzMegaHertz (MHz) 10^6 Hz
800,000 kHzKiloHertz (kHz) 10^3 Hz
800 MHzMegaHertz (MHz) 10^6 Hz
Frequency Range 30 MHzMegaHertz (MHz) 10^6 Hz30,000,000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
30,000 kHzKiloHertz (kHz) 10^3 Hz
- 800 MHzMegaHertz (MHz) 10^6 Hz800,000,000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
800,000 kHzKiloHertz (kHz) 10^3 Hz
Mode NFMNarrowband Frequency Modulation
Modulation MFSKMultiple Frequency Shift-Keying
ACF
Bandwidth 3.3 kHzKiloHertz (kHz) 10^3 Hz3,300 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
0.0033 MHzMegaHertz (MHz) 10^6 Hz
3.3 kHzKiloHertz (kHz) 10^3 Hz
0.0033 MHzMegaHertz (MHz) 10^6 Hz
3.3 kHzKiloHertz (kHz) 10^3 Hz
0.0033 MHzMegaHertz (MHz) 10^6 Hz
Location Worldwide
Short Description DTMF is a signaling mode used for a variety of purposes. It's most known for telephony dialing, but is in use for many different applications such as DTMF paging for DTMF-enabled VHFVery High Frequency (30-300 MHz)/UHFUltra High Frequency (300-3000 MHz) radios.
I/Q Raw Recording
Audio Sample
DTMF is a signaling mode used for a variety of purposes. It's most known for telephony dialing, but is in use for many different applications such as DTMF paging for DTMF-enabled VHFVery High Frequency (30-300 MHz)/UHFUltra High Frequency (300-3000 MHz) radios and as a marker on broadcasting stations for switching between regional and local programming for events like local news broadcasting.

DTMF uses the dual-tone method, where each symbol is represented by a combination of two distinct tones.

DTMF Table.png


The A,B,C, and D tones are actually originally part of an old US Military telephone system called Autovon.

  • A (697/1633): Flash Override (FO)
  • B (770/1633): Flash (F)
  • C (852/1633): Immediate (I)
  • D (941/1633): Priority (P)

These keys were for the urgency of the call. The highest, Flash Override, would effectively interrupt all ongoing calls and give the speaker full command. This system began operation in 1966 and ended in the early 1990's when a newer system, the Defense Switched Network, replaced Autovon.

Nowadays, the ABCD keys (as well as * and # ) are used infrequently and are for operations unrelated to their original purpose. On telephone networks, such keys are used for network control, such as cycling through different carriers. For amateur radio and commercial two-way radio systems, the keys are used for equipment control, repeater control, remote base operations, and some telephone communications systems.

The tone duration of DTMF is variable depending on the system used. Standard Whelen timing is 40ms tone, 20ms space, where standard Motorola rate is 250ms tone, 250ms space. Federal Signal ranges from 35ms tone 5ms space to 1000ms tone 1000ms space. Genave Superfast rate is 20ms tone 20ms space. Genave claims their decoders can even respond to 20ms tone 5ms space.

In general, DTMF's speed when being send manually (as people type on a DTMF keypad) will be variable and not rigidly structured, as in tone length and space length will happen loosely as the keys are pressed. Electric systems using DTMF dialing will be rigid and have equal tone and break lengths between tones.


Samples[edit]

x/y, x=tone duration, y=space duration

Normal 50/50 Motorola 250/250 Whelen 40/20
Dtmf page normal 50 50.jpg
Motorola rate 250ms.png
Dtmf whelen 40 20.jpg

Genave 20/20 Genave 20/5
Dtmf genave superfast 20 20.png
Dtmf genave superfast 20 05.png

Decoding Software[edit]

Hobby Level Software

Video Examples[edit]

Additional Links[edit]

Additional Images[edit]