Tektronix 2715, Руководство пользователя

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CATV Measurements
2715 User Manual
5–51
The Single-Sweep mode is designed to minimize the time that the carrier must
be turned off. The Single-Sweep mode is not available when in-service basis is
selected.
First, the instrument measures the peak of the video carrier on the current
channel, then pauses and prompts you to turn off the carrier.
In this mode, the instrument scans the signals at frequencies specified in the
setup table relative to the carrier frequency. Absolute frequencies are ignored. If
no frequencies are specified, the instrument uses the default frequencies. From
these it creates a single-sweep test table. It then computes sweep limits that
include all the frequencies found in the single-sweep table (with 250 kHz of
oversweep at each end). It takes a single sweep using a 30 kHz RBW and no
video filter. It checks each of the frequencies in the single-sweep test table to see
that the signals there are neither too near the bottom of the screen nor too near
the top for a safe measurement. If necessary, it adjusts the reference level to
ensure that the measurement can be made accurately. It then turns on the 100 Hz
video filter and sweeps again. It now prompts you to turn the carrier back on and
proceeds to measure all the beats specified in the single-sweep test table using
the single sweep data.
Press [CATV/APPL] to call up the CATV MEASUREMENTS menu. See
Figure 5–1.
The Continuous mode is designed to run CSO tests repeatedly for 24 hours. It
assumes that the carrier of the channel-under-test has been turned off and will
remain off for the duration of the test. The Continuous mode is not available
when in-service basis is selected.
The frequency of the reference carrier is selectable either as an absolute
frequency, or as a frequency relative to the carrier of the channel-under-test. The
default is –6 MHz relative. The carrier is assumed to be stable in frequency to
within
±
200 kHz.
The frequencies of the beats may be specified only relative to the carrier of the
channel-under-test. At least one beat frequency must be specified for the test to
run. The beats are assumed to be within
±
50 kHz of the specified frequencies.
The interval at which the continuous CSO repeats is selectable from 15 seconds
(default) to 21600 seconds (6 hours) in one second increments.
The 2715 periodically runs a subset of normalizations throughout the test. These
normalizations take about 3 minutes. The interval is selectable from 1 hour
(default) to 24 hours in one hour increments. Selecting 24 hours has the effect of
turning the periodic normalization off.
Single-Sweep Mode
Continuous Mode