The presence of the TETRA CODEC makes the measurement of distortion very difficult. GSM has the same problem and measures the terminal distortion between the ear/mouth and the GSM CODEC in order to avoid artifacts introduced by the CODEC [GSM 03.50]. This section follows the GSM approach and measures the distortion within the TETRA terminal.
The distortion is measured between the Mouth Reference point and the Linear PCM Reference Point within the terminal. Measurements are made for both handset and headset terminals.
The ratio of signal-to-total distortion power measured with the proper noise weighting [G.223, table 3] and shall be above the limits given in table 1 below unless the applied sound pressure level at the Mouth Reference Point exceeds +10dBPa. There is no sending distortion requirement for signals above +10dBPa. Test frequency shall be in the range 1004 to 1025 Hz.
The ARL is determined by adjusting the level of the test signal until the output at the Linear Reference Point is -10dBm0. This signal is then the ARL.
| Sending Level relative to ARL | Sending Ratio (dB) |
|---|---|
| -35 | 17.5 |
| -30 | 22.5 |
| -20 | 30.7 |
| -10 | 33.3 |
| 0 | 33.7 |
| +7 | 31.5 |
| +10 | 25.5 |
| Note 1: The limits at intermediate frequencies lie on straight lines drawn between the given values on a linear(ARL) - linear(dB) scale | |
The distortion is measured between the Ear Reference point and the Linear PCM Reference Point within the terminal. Measurements are made for both handset and headset terminals.
These measurements shall be made at the nominal setting of the volume control.
The ratio of signal-to-total distortion power measured with the proper noise weighting [G.223, table 3] and shall be above the limits given in table 3 below unless the sound pressure level at the Ear Reference Point exceeds +10dBPa. There is no receive distortion requirement for levels above +10dBPa. Test frequency shall be in the range 1004 to 1025 Hz with a digitally generated sine wave.
| Receive Level | Receiving Ratio (dB) |
|---|---|
| -45 | 17.5 |
| -40 | 22.5 |
| -30 | 30.5 |
| -20 | 33.0 |
| -10 | 33.5 |
| -3 | 31.2 |
| 0 | 25.5 |
| Note 1: The limits at intermediate frequencies lie on straight lines drawn between the given values on a linear(dB level) - linear(dB Ratio) scale | |
This is measured between the Ear Reference point and the Linear PCM Reference Point within the terminal.
The variation of gain with respect to input level shall be within the limits of the table below. Test frequency shall be in the range 1004 to 1025 Hz. There is no receive gain variation requirement for levels above +10dBPa.
| Receive Level | Upper Limit (dB) | Lower Limit (dB) |
|---|---|---|
| 3 | 0.5 | -0.5 |
| -10 | 0.5 | -0.5 |
| -40 | 0.5 | -0.5 |
| -40 | 1 | -1 |
| -50 | 1 | -1 |
| -50 | 2 | -2 |
| Note 1: The limits at intermediate frequencies lie on straight lines drawn between the given values on a Linear(dB Level) - linear(dB limit) scale | ||
Copyright ©2002 Andy Fletcher andy@x31.com