I
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Channel Measurements
Making Channel Measurements
Hints
1. For best results, the channel carrier-to-noise ratio should be 40
dl
or greater
lin
a 4 MHz noise
I
bandwidth).
2. The hum test requires a carrier wave or NTSC signal. It cannot give meaningful results when
a channel uses sync suppression scrambling (unless the measurement is made at the subscriber
terminal output of a
descrambler).
Measuring hum with video modulation present requires that all
sync tips have the same general level in order to measure their variation.
When the hum test is performed on channels with sync suppression scrambling, it gives completely
meaningless numbers.
2-50
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