User`s guide

34 Chapter 2

S:\agilent\83217\OPT001\BOOK\CHAPTERS\tdscrip.fm

Test Descriptions

TEST_12 - TXA Compressor Response

Description

This test measures the compressor’s zero reference deviation and

operating range. For every 2 dB change in input level, there should be a

nominal output level change of 1 dB.

NOTE

Audio connections from the radio to the test system are required for this

test.

Compressor response is expressed in dB of tracking error over the

indicated operating range.

• The deviation is set to 2.9 kHz (1.5 kHz for narrow analog) and a

reference is taken with both the rms*sqr(2) and pk+ detectors.

• Compressor response to different input levels is measured.

• The input is varied from a start level equal to parameter 38. TXA

Compressor Start Level (dB) to a stop level equal to parameter 40.

TXA Compressor Stop Level (dB) using the step level parameter 39.

TXA Compressor Step Level (dB).

•If parameter 38. TXA Compressor Start Level (dB) is less than

parameter 40. TXA Compressor Stop Level (dB) then the step value

retrieved from parameter 39. TXA Compressor Step Level (dB) is

made positive. Otherwise, it is made negative. The peak deviation is

measured at each step using either the rms*sqr(2) or pk+ detector

and the compressor response relative to the reference is calculated

using the appropriate reference value for the detector used.

• The compressor typically limits relative inputs

≥17.6 dB; therefore,

the lower limit is calculated from the upper limit when the relative

input deviation is

≥17.6 dB using the formula: (8.8-upper

limit)-(present input deviation/2).

Background

A compressor is used in the phone’s voice input circuitry to decrease the

variability of the modulation due to volume changes from the talker. In

combination with an expandor in the cell site receiver, this provides

improved signal-to-noise-ratio in the demodulated audio.

Pass/Fail Limits Used

• 14. TXA Compressor Tracking Error <0dB (dB)

• 15. TXA Compressor Tracking Error >0dB (dB)