Agilent Technologies 8935 series e6380a manual Twist and Pre-emphasis Interaction, Example

Signaling Encoder and Decoder - Screens and Control Fields

Control Fields for the Signaling Encoder and Decoder

Twist

Twist is the ratio of amplitudes (in dB) between the high frequency and low frequency tone in each DTMF pair. A positive value indicates a higher amplitude for the high frequency tones. A negative value indicates a higher amplitude for the low frequency tones.

The amplitude of the combined tones is set in the AFGen2 To field.

	Twist and Pre-emphasis Interaction
	Twist and Pre-emphasis affect the relative levels of the high and low
	tones within each symbol (tone pair). If pre-emphasis is off, twist sets
	the difference in deviation (in dB) between the high and low tones. If
	twist is off, pre-emphasis places a 6 dB per octave difference in
	deviation between the high and low tones. If both twist and
	pre-emphasis are on, the two effects are summed.
	For most conditions, set Twist to 2.5 dB, Pre-Empon, and 60% rated
	deviation (3 kHz for a typical 5 kHz deviation rated receiver).
	“Examples of Twist and Pre-emphasis Interaction” on page 279
	Examples of Twist and Pre-emphasis Interaction
Example 8-3	Example 1:
	3 kHz deviation, Twist 0 dB, Pre-emphasis off.
	The level of each low tone and high tone individually generate 1.5 kHz
	deviation. The tones are summed to produce 3 kHz deviation.
Example 8-4	Example 2:
	3 kHz deviation, Twist 2.5 dB, Pre-emphasis off.
	The high tone has 2.5 dB (a factor of 1.334) more deviation than the low
	tone. The two tones are summed to produce 3 kHz peak deviation.
	Therefore, the low tone’s deviation is 1286 Hz and the high tone’s
	deviation is 1714 Hz.
Example 8-5	Example 3:
	3 kHz deviation, Twist 0 dB, Pre-emphasis on.
	There is a 6 dB per octave difference between the high and low tones.
	For example, if sending a 1, which has a low tone of 697 Hz and a high
	tone of
	1209 Hz, the high tone has a deviation of 1209/697 = 1.735 times the
	low tone’s deviation. The high tone’s deviation is then 20 ⋅
	log(1209/967) = 4.78 dB higher than the low tone. Since their sum must
	equal 3 kHz, the low tone’s deviation is 1097 Hz, and the high tone’s
	deviation is 1903 Hz.

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