If digital measurements are active, turn them off or set their trigger source to Immediate. See Triggering of Measurements .
Both FM distortion and audio distortion measurements are available in the test set. Make sure you are querying the FM Distortion measurement (FETCh:FM:DIST?) in your program and not the audio distortion measurement (FETCh:AFAN:DIST?) when making an FM distortion measurement.
Be sure to use the type of detector specified for deviation measurements in the applicable standard. For example, if the measurement specification is for peak deviation, be sure to use the Peak+ or Peak- detector instead of the RMS detector. If the signal being measured is noisy, you can use the RMS detector to make a more stable measurement and then multiply the result by 1.414 to arrive at the peak value.
All measurements are performed after any filtering, de-emphasis, and expansion are performed. When measuring SAT deviation and frequency, the Filter Type should normally be set to 100 Hz BW BPF and the 100 Hz BW BPF Center Frequency should be set to the SAT frequency. The C-message filter is often used for measurements made on signals with FM rates in the normal voice frequency range (such as the 1004 Hz tone used for distortion measurements).
The expected signal frequency (or AVC channel number) and input level must be specified in your program for accurate measurements. This is done either through the base station emulator settings, when the mobile is first put on an AVC, or by manually controlling the test set's measurement receiver. See Active Cell Operating Mode , Active Cell Operating Mode , and Receiver Control for information on setting the expected input frequency.
To meet performance specifications, the input signal must be in the frequency range of 800 MHz to 960 MHz or 1.70 GHz to 2.0 GHz, and be within 2.5 kHz of the expected input frequency, at a power level (at the RF IN/OUT connector) of -15 dBm to +40 dBm. The specified FM deviation range is 0 Hz to 16 kHz, at a modulation rate of 100 Hz to 15 kHz. FM Distortion is specified over the modulation rate range of 100 Hz to 10 kHz.
See Integrity Indicator .
If over range (5) is returned; the input power has exceeded the test set's internal sampler maximum value by at least 6 dB during some part of the sampling or the input power has exceeded the calibrated range of the test set's power detector for the expected power setting.
If under range (6) is returned; the measured input power is more than 20 dB below the expected input power level. Under range is also indicated if the input power is more than 2 dB below the calibrated range of the test set's power detector (-30 dBm). If the expected input power setting is correctly set for the signal level into the test set, an under range condition can still occur if the receiver has not been tuned to the signal's frequency.