Agilent Technologies 8935 series e6380a manual De-emphasis Effects on Input Level

Signaling Encoder and Decoder - Screens and Control Fields

Control Fields for the Signaling Encoder and Decoder

Input Level

This field specifies the expected data signal level (after de- emphasis if used). The higher the level of signal expected by the analyzer, the higher the trigger level is set. See “De-emphasis Effects on Input Level” on page 266.

Operating Considerations

The unit-of-measure is determined by the AF Anl In setting.

The input level should be set high enough to prevent false triggering, but low enough to allow triggering for valid signals (typically about 3 kHz). This you to set the input level well below the expected level.

When using de-emphasis, the Input Level setting may need to be reduced significantly to properly decode the incoming signal. De-Emphasis is enabled/disabled using the De-Emphasisfield on the AF ANALYZER screen.

If de-emphasis is used (by setting the AF Analyzer’s De-Emphasisfield to 750 ∝ s), the Input Level should be set to about 1/5 of the measured signal’s level. For example, a 1 kHz, 1 Vpeak sinewave into the AF Analyzer’s input requires an Input Level of approximately 0.212 V to trigger correctly.

De-emphasis Effects on Input Level

De-emphasis is a single-pole, low-pass filter with a 212.2 Hz corner frequency. It is enabled/disabled using the De-Emphasisfield on the AF ANALYZER screen. The input level is the expected level at the output of the de-emphasis network.

Assuming a mean DTMF frequency of approximately 1 kHz, decoding with de-emphasis on (set to

750 ∝ s) requires the input level to be set to 212/1000 = 0.212 times the peak deviation, or about 1/5 the incoming level of the tone.

266 Chapter 8

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