Tektronix 2715, User Manual

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CATV Measurements
2715 User Manual
5–63
The test signal line number is the number of the field line on which the test
signal is inserted for in-service testing. For television systems using the National
Television System Committee (NTSC) standard, this typically is on line 10
through line 20 of field 1 and line 9 through line 19 of field 2. However, the
2715 counts field lines consecutively from 1 to 525. Therefore, the range of
potentially valid line numbers for the test signal will be 10 through 20 (for
odd-numbered fields) or 272 through 282 (for even-numbered fields). For
systems using the Phase Alternation Line (PAL) standard, the test signal line
number is typically line 6 through line 20 and line 318 through line 332.
NOTE . If the only quiet lines available are beyond the ranges listed above, then
you must specify the quiet line in the channel table, using the Cable TV RF
Measurements Software for Windows provided with your instrument. In this
case, the in-service test is run on the specified line, even though it is outside the
normal range, but there is no verification that the line is still quiet after the test.
Select the measurement mode from the IN-CHAN RESP SETUP menu before
initiating the test. The Interactive mode assists you in selecting a pair of
measurement points. The Automatic mode allows measurement levels at up to
five locations that are entered using the IN-CHAN RESP SETUP menu. If you
did not choose the in-service basis, you will be prompted to replace the
modulated signal with a test signal for either interactive or automatic modes.
NOTE
. When doing the In-Channel Response test in-service and if the channel
under test has a carrier level of –2 dBmV or less, it is necessary to turn on the
preamp and select an RF attenuation setting such that a 1st mixer input level of
–2 dBmV or greater is maintained.
When the measurement is initiated, the instrument does the following:
H
Enables peak acquisition mode
H
Sets the reference level so that the peaks of the detected test signal are placed
in the top major division while the instrument is in the 10 dB/div mode
H
Sets the vertical mode to 1 dB/div
H
If measuring on in-service basis, enables gating on the specified TV line and
performs a slow sweep
H
In interactive mode, the instrument prompts you to move the marker to the
first location (for example, the lowest detected burst packet in a Multiburst
signal) and press [W] to make the first measurement. Then the instrument
prompts you to move the marker to the second location (for example, the
highest detected burst packet) and press [W] to make the second measure-
ment. The instrument then calculates the difference between the two