Touch-Tone Information

The standards for tone "dialing" are as follows:

Each Touch-Tone digit is represented by a unique pair of tones as shown in left image above. One tone from the low tone group (represented by the blue lines and blue frequency numbers), and one tone from the high tone group (represented by the red lines and red frequency numbers), are mixed together to form a "Dual-Tone Multi-Frequency" signal.

Type 66 Autovon Dial (shown above, right image):

[Photo and button designations courtesy of Stephen (Steph) Kerman]

The Autovon legends are:

• FO = Flash Override
• F = Flash
• I = Immediate
• P = Priority

AUTOVON - History and description - From http://public.afca.scott.af.mil/:

A major development in long-haul communications in the early 1960s was the Automatic Voice Network, commonly called AUTOVON. Activated in December 1963, AUTOVON, derived from the Army’s Switched Circuit Automatic Network, was designed to provide the Department of Defense with an internal telephone capability to replace toll and Wide Area Telephone Service (WATS) calls, while also allowing precedence preemption for high priority users. Development of the AUTOVON system represented one of the most significant and comprehensive telecommunications programs ever undertaken by the DOD. While the dedicated circuits used in earlier networks provided good response time, weaknesses in survivability and reliability were significant problems. The loss of a single circuit between two points disrupted communications between subscribers, and each termination placed on the dedicated circuit required a separate instrument. AUTOVON did much to correct these deficiencies.

AUTOVON became the principal long-haul, nonsecure voice communications network within the Defense Communications System. The network served the entire Department of Defense and handled essential communications concerning command, operations, and administration. It was a global network comprised of interconnected automatic switching centers and thousands of subscriber terminals throughout the world. Over the next 25 years, the network would be continually modernized and expanded to provide more service and capabilities to the users. Finally, it became a part of the new Defense Switched Network (DSN), the replacement system activated in 1990 to provide long-distance telephone service to the military.

Some historical trivia - In the late 60’s and early 70’s the "#" symbol was standardized as a preface to indicate that the call was to be a Picturephone (video) call. Picturephone service was offered in a few markets (Chicago, NY) until it was killed about 1973. For business callers with a multiline keyset (2565), the line lamp would change from a white light to a red light (special polarity sensitive "dual"color lamps) once the "#" key was pressed. - Courtesy of Rick Walsh.

To view schematics and information on the
Touch-Tone dials used in Western Electric phones,
click on the two links below:

Type 35 Dial Schematic

Type 72 Dial Schematic and Information Page

In order for the central-office receiver to register the digit properly, the tone-address signals must meet the following requirements:

1) Signal Levels:
Nominal level per frequency: -6 to -4 dBm. Minimum level per frequency: Low Group, -10 dBm; High Group, -8 dBm. Maximum level per frequency pair: +2 dBm. Maximum difference in levels between frequencies: 4 dB.

2) Frequency Deviation: +/- 1.5 percent of the values given above.

3) Extraneous frequency components: The total power of all extraneous frequencies accompanying the signal should be a t least 20 dB below the signal power, in the voice band above 500 Hz.

4) Voice Suppression: Voice energy from any source should be suppressed at least 45 dB during tone signal transmission. In the case of automatic dialing, the suppression should be maintained continuously until pulsing is completed.

5) Rise Time: Each of the two frequencies of the signal should attain at least 90 percent of full amplitude within 5 ms, and preferably within 3 ms for automatic dialers, from the time that the first frequency begins.

6) Pulsing Rate: Minimum duration of two-frequency tone signal: 50 ms normally; 90 ms if transmitted by radio. Minimum inter-digital time: 45 ms.

7) Tone leak during signal off time should be less than -55 dBm.

8) Transient Voltages: Peak transient voltages generated during tone signaling should be no greater than 12 dB above the zero-to-peak voltage of the composite two-frequency tone signal.