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Chapter 4, Mobile Station Analog Tests
Receiver Audio Distortion and Hum and Noise (requires audio connections)
Measurement Overview
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Receiver Audio Harmonic Distortion is measured with the Test Set providing an
FM signal to the mobile station, modulated by a test tone from the Test Set's
audio frequency generator. (A SAT tone is also present on the RF signal). To
measure distortion, the audio signal from the mobile station's earpiece (receiver
output) is cabled to the Test Set's AUDIO IN connector. The Test Set's audio
analyzer measures the level of the audio output, then notches out the test tone and
measures only the RMS harmonic content produced by the audio signal.
Distortion is then displayed as the percentage of mobile station receiver output
level that was due to the harmonic content.
Typically, Audio Harmonic Distortion should be less than 5%.
Receiver hum and noise uses essentially the same setup as distortion, except that
the modulation source is turned off, and residual FM is measured. The hum and
noise measurement is the ratio of AC level from the mobile station's receiver
without modulation to AC level with modulation.
Typically transmitter Hum and Noise should be at least 32 dB below levels with
modulation on.
SINAD, a measure of receiver sensitivity, also uses essentially the same setup as
distortion, except the RF amplitude to the mobile station's antenna input is
lowered until 12 dB SINAD is reached. SINAD measurements are the ratio of the
test signal plus noise and distortion components to just the noise and distortion.
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