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Chapter 4, Mobile Station Analog Tests
Transmitter Audio Distortion and Hum and Noise (requires audio connections)
7. Make the transmitter hum and noise measurement.
1. Position the cursor in front of the audio
frequency generator level field as shown. Press
the ON/OFF key.
The Lo and Hi limit annunciators should be
flashing.
The FM Deviation field will display the FM hum
and noise level. It should be at least 32 dB
lower than the reference level.
Setting the 0 dB reference allowed the Test Set to display the ratio of FM without modulation (residual FM) to
FM with the test signal applied, in the FM Deviation field.
Measurement Overview
86
Transmitter Distortion (and Noise) is measured with a test tone adjusted to
frequency modulate the mobile station's transmitter with a specified deviation.
The FM signal from the mobile station's transmitter is demodulated by the Test
Set using a C-message weighted filter, and distortion and noise are measured.
Typically, distortion should be less than 5%.
Transmitter Hum and Noise is measured by modulating the mobile station's
transmitter with a test tone adjusted to produce a specified amount of deviation.
With the signal from the mobile station's transmitter demodulated by the Test Set
using a C-message weighted filter, the amount of deviation is recorded. To
determine the hum and noise, which is caused by residual FM, the modulation is
removed and the ratio of residual FM to FM with the test signal on is calculated.
Typically, FM Hum and Noise should be less than
−
32 dB.
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