Last updated: December 3, 2008
This measurement is not applicable to GPRS or EGPRS.
You can use the multi-tone audio measurement to verify the performance of a mobile station's speaker and microphone. This is made possible by the two measurement modes available: downlink and uplink. Audio level, frequency response, and distortion results are available for both modes.
In both modes, there is an audio stimulus, referred to as the "Generator", and an audio analysis, referred to as the "Analyzer". The Generator is a 20 tone source. Presets are provided, which contain frequency and level setting for all 20 tones, or you can specify the frequency and level for each tone. You can choose to have the Analyzer tuned to the same frequencies as the Generator, or you can configure the Analyzer separately.
The multi-tone audio measurement measures Audio Level (V), SINAD (dB), Distortion (%), and Audio Frequency. When measuring a mobile's audio output, the audio signal may come from either an acoustic coupler or from a test interface connection to the mobile's audio circuitry.
The downlink measurement mode is used to test the mobile station's speaker quality. The tones from the Generator are encoded and sent to the mobile station over the RF link. The mobile station decodes the audio and sends it to the speaker. The audio signal travels through an acoustic coupler to the test set's AUDIO IN port and then to the Analyzer. Measurement results are available for each tone either graphically from the test set's front panel or programmatically using a GPIB query.
The
Speech
TCH parameter must be set to
Multi-Tone
for downlink measurements. Setting the speech type to
Multi-Tone
connects the multi-tone generator to the encoder and ensures the audio signal gets placed on the RF link.
The
Expected Audio In Peak Voltage
should be set appropriately to avoid over or under range errors.
The AUDIO IN connectors feed the inputs to a floating-input differential amplifier, with each input having an impedance of about 100,000 ohms to chassis ground. For best noise immunity, connect the audio signal and its ground reference to the two input ports through shielded coaxial cables, or input the signal to the AUDIO IN HI connector and ground the AUDIO IN LO connector's center contact.
The uplink measurement mode is used to test the mobile station's microphone quality. The Generator sends the audio tones to the test set's AUDIO OUT port. An acoustic coupler is used to connect the AUDIO OUT port to the mobile station's microphone. The mobile station encodes the audio signal and transmits it back to the test set using the RF link. The test set decodes the audio signal and sends it to the Analyzer. Measurement results are available for each tone either graphically from the test set's front panel or programmatically using a GPIB query.
The
Speech
TCH parameter must be set to
None
for uplink measurements. This ensures there is no downlink signal, which would cause bad measurement results.
You should adjust the downlink Generator levels as high as possible to achieve a strong signal on the uplink. This will help prevent the low level portions of the signal from being buried in the noise floor. The downlink Generator level upper limits are dynamic, depending on the generator frequency configuration. You can see this difference when a call is connected and audio is being supplied to the mobile station's microphone. For example, the preset Multi-tone 100 has a lower crest factor and therefore allows the total downlink generator to be set to a higher level than the Multi-tone 140, whose crest factor is larger and therefore would cause signal level peaks which exceed the hardware limitations if it's total limit is set too high.
When the SINAD/Distortion State is ON, the test set returns SINAD, Distortion, Audio Level, and Audio Frequency results for audio tone one. In this mode, it is also possible for you to make a distortion level when no tone is being generated. This allows you to detect spurs from the mobile station.
The SINAD/Distortion measurements used by the Multi-tone Audio instrument and the Audio Analyzer use the same algorithms. The primary difference is the Multi-tone Audio instrument allows you to make these measurements on audio that has been sent to the test set over RF instead of only through the AUDIO IN BNC connectors.
Analyzer Reference Tone
is used to specify a reference other than 0 dB if this parameter is set to
Relative
.
Analyzer 0 dB Reference Mode
must be set to
Relative
for this parameter to be active.
Analyzer 0 dB Reference Mode
must be set to
Absolute
and the
Measurement Mode
must be set to
Downlink
for this parameter to be active.
Analyzer 0 dB Reference Mode
must be set to
Absolute
and the
Measurement Mode
must be set to
Uplink
for this parameter to be active.Multi-Tone Audio Troubleshooting
Programming a Downlink Multi-Tone Audio Measurement
Programming an Uplink Multi-Tone Audio Measurement
Statistical Measurement Results (Multi-measurements)