Tektronix 2715, Руководство пользователя

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Spectrum Analyzer Menus
2715 User Manual
6–47
11. Press [9] to select the Setup Table.
12. Press [1] to select NORM BW FOR C/N.
13. Press [5] [X] to enter 5 MHz for the noise bandwidth for the carrier-to-noise
(C/N) measurement.
14. Press [BKSP] to return to the Applications menu.
15. Press [1] to turn on the C/N feature.
The spectral display reappears with the fixed marker on top of the 100 MHz
signal peak (the 2715 places the fixed marker on the signal peak nearest the
center of the screen in the C/N mode). The moveable marker appears
1 division from the left screen edge.
16. Reposition the moveable marker 50 MHz above the signal.
NOTE
. The moveable marker is initially positioned only to clearly separate it
from the fixed marker. You must place the noise marker at the frequency where
you want the noise measured.
The first two items in the right on-screen column read approximately as
follows:
C/N 63.0DB
@ 5.0MHZ
The reading may vary slightly. You will also receive the NOISE LEVEL
LESS THAN 2DB warning.
The C/N reading is the ratio of the signal power at the fixed marker’s position to
the average noise power at the movable marker position. The noise reading is
corrected as indicated in the normalized noise measurement section. Since the
noise level measured earlier was approximately –44.2 dBmV and the signal peak
is 18.8 dBmV, the ratio should be approximately 63 dB.
The preamplifier discussed with the INPUT menu in this section can be very
important when making noise or C/N measurements in broadband networks. For
instance, in the U.S., good cable television operating practice requires that the
video signal be at least 0 dBmV while picture quality requires the noise to be
approximately 43 dB lower, or approximately –43 dBmV in a 4 MHz band.
17. Press [CATV/APPL] to call up the Applications menu.
18. Press [9] to select the Setup Table.
19. Press [1] to select NORM BW FOR C/N.