DTMF Measurement Description

Last updated: June 20, 2006

How is a DTMF measurement made?

The DTMF (Dual Tone Multiple Frequency) measurement detects dual tone multi-frequency signals generated by the mobile station.

The DTMF signals indicate which symbol was pressed on the mobile station's keypad. The set of valid symbols is 0-9, *, #, A, B, C and D. Each DTMF signals consists of two tones that are generated together. One tone is from a set of lower frequencies (697 Hz, 770 Hz, 852 Hz, 941 Hz) and the other one is from a set of upper frequencies (1209 Hz, 1336 Hz, 1477 Hz, 1633 Hz). The specific DTMF frequencies that are associated with valid symbols are shown in the following table.

DTMF Frequencies Matrix
	1209 Hz	1336 Hz	1477 Hz	1633 Hz
697 Hz	1	2	3	A
770 Hz	4	5	6	B
852 Hz	7	8	9	C
941 Hz	*	0	#	D

NOTE

The far right column, 1633 Hz, is not defined in the Test Standard EIA/TIA-690, but in a common-used set of symbols that is defined in the Bell Standard. It is included in this measurement for compatibility with the Bell Standard.

When the measurement is initiated, the test set monitors the carrier for the period defined by the gate time. When the period is reached, the captured signal is processed. The DTMF measurement measures the frequency and frequency error of each tone in the DTMF symbol and the phase deviation caused by each tone in the DTMF symbol. The length of time that each DTMF symbol, the time between symbols and the detected DTMF symbols are reported.

Operating Consideration

This measurement is available in Active Cell operating mode, AVC Test operating mode and CW operating mode.

DTMF Measurement Parameters

The DTMF measurement setup menu provides control over the following parameters

Gate Time (See SETup:DTMF:GTIMe ) - Sets the length of time that the DTMF measurement samples the signals under test.
Detector Type (See SETup:DTMF:DETector[:TYPE] ) - Sets the type of detector to use when making DTMF measurements: RMS, Peak+, Peak-, Peak+/- Max and Peak +/- /2.
- The Peak+ and Peak- detectors measure the greatest positive or negative frequency excursion in carrier frequency during the sample.
- The RMS detector measures the root mean squared value. This setting does not affect the distortion measurement.
- The Peak+/- Max detector measures both greatest positive and negative peaks and take the absolute value of each, then return the greater one.
- The Peak+/- /2 detector measures both greatest positive and negative peaks and take the absolute value of each, then returns average value.
Trigger Arm (See Trigger Arm (Single or Continuous) Description ).
Measurement Timeout (see Timeouts ).

DTMF Measurement Results

Integrity Indicator (See Integrity Indicator ).

For all 16 characters, the following results are returned for each character (See FETCh:DTMF:CHARacter? <num value> )

Symbol Result - Indicate the character sent by the mobile station.
Low Tone Frequency Result - Indicate the measured frequency of lower tone of DTMF signal.
Low Tone Frequency Error Result - Indicate frequency error, which is the difference between the measured frequency and the expected frequency, of the lower tone of DTMF signal.
Low Tone Phase Deviation Result - Indicate the radian deviation caused by the lower tone of the DTMF signal.
High Tone Frequency Result - Indicate the measured frequency of upper tone of DTMF signal.
High Tone Frequency Error Result - Indicate the radian deviation caused by the upper tone of the DTMF signal.
High Tone Phase Deviation Result - Indicate the radian deviation caused by the upper tone of the DTMF signal.
On Time Result - Indicate the amount of time during which the DTMF signal is On
Off Time Result - Indicate the amount of time during which the DTMF signal is Off

A typical measurement result is shown below.

Input Signaling Requirements

The test set measures the low group and high group tones within the frequency ranges defined in the following table.

DTMF Measurement Expected Frequency Ranges
Expected DTMF frequency (Hz)	Measurable Lower Limit (Hz)	Measurable Upper Limit (Hz)
Lower Tone
697	>=663	<733
770	>=733	<810
852	>=810	<895
941	>=895	<989
Upper Tone
1209	>=1150	<1271
1336	>=1271	<1405
1477	>=1405	<1553
1633	>=1553	<1717

The duration of DTMF symbols must be at least 45 ms and the time between symbols must be at least 10 ms.

The DTMF measurement meets or exceeds specifications when the following input signal requirements are met:

The input signal is an RF carrier that is frequency modulated to include a DTMF symbol. The input signal must be within +/- 2.5 kHz of the test set' s expected frequency.
The deviation that is caused by a SAT or ST tones or by a wideband data burst is not included in the deviation result. The ratio of the input signal' s deviation to residual FM must be greater than 30 dB.

Key TIA/EIA-690 Test Using the DTMF Measurement

See Measuring DTMF Testing 10.1 Dual Tone Multifrequency (DTMF) Signaling