Part II: Settings and Measurements
8-3 Digital
HUM
Hum modulation, or power source frequency modulation distortion, comes from a power source frequency
interference. HUM modulation generally degrades MER values of a digital carrier. The DS2831 supports hum
modulation measurements for digital channels. The measurement interface is shown below.
8-3.1 Settings
Channel The channel to measure. You can select any active channel in the active channel plan.
Frequency Input range 5-1200 MHz.
Button Operation
[50Hz] / [60Hz] Toggles the power frequency between 50Hz and 60Hz.
Hold: Pauses the measurement. Press again to resume.
Test Results
Average Power: Measured over the occupied bandwidth (Level).
Hum Modulation: Degree of hum modulation interference, as measured under the digital QAM carrier.
(DOCSIS specification recommends not to exceed 5%; the less, the better.)
Freq Component: Displays the percentage of HUM for each of the distortion frequencies.
You can choose the AC power frequency according to your local region.
The DS2831 can measure the following low-frequency interference and interference harmonics:
•
50Hz:
100Hz, 150Hz and 200Hz
•
60Hz:
120Hz, 180Hz and 240Hz
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