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NOTE: If the C/N measurement value is outside the specified range,
the numerical result will change from black to gray.
To edit the bandwidth, press the
BW
soft key. The bandwidth can
be adjusted by using the
UP
and
DOWN
arrow keys or by entering a
value using the numeric keypad and then pressing the
ENTER
key.
The FCC specification for C/N measurements is a bandwidth of
4.200 MHz. CATV organizations outside of the United States may
have different requirements. Measurement BW can also be defined
individually for each channel in the Channel Plan setup menu.
Noise Offset Frequency Adjustments
The frequency at which the noise level is measured is the Carrier
frequency plus the noise offset. To adjust the noise offset, press the
OFFSET
soft key. The offset can be adjusted by using the
UP
and
DOWN
arrow keys or by entering a value using the numeric keypad
and then pressing the
ENTER
key. Noise Offset values can also be
defined individually for each channel in the Channel Plan setup
menu.
Note: BW and Noise Offset values can be defined individually for
each channel (see section 4.3.4 "How To Edit Channel Parameters").
When tuning by channel number, the BW and Noise Offset values
are obtained from the channel plan. After tuning to a channel, the
values can be adjusted using the Offset and BW soft keys. However,
these adjustments will affect the C/N screen only and will not change
the setup values in the channel plan.
4.8 HOW TO MEASURE HUM
Hum is undesirable modulation of the television video carrier by
power line frequencies and harmonics (e.g., 60 or 120 Hz), or other
low frequency disturbances (FCC limit: < 3%). To measure Hum,
simply press the
Hum
key when tuned to any non-scrambled chan-
nel. In the Hum mode the hum modulation of the tuned channel or
frequency will be displayed in either % or dB as selected by the
operator. The units setting selected in the Hum screen (% or dB) will
determine which units will be used to measure Hum during subse-
quent Auto Tests. Be sure to set the desired units in the Hum screen
Summary of Contents for 3SR
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