Chapter 5: Analog Non-Linear Distortion Tests; Cnr - Deviser S7200 User Manual

Part II: Settings and Measurements

Chapter 5: Analog Non-Linear Distortion Tests

This chapter contains instructions and concepts for the CNR (carrier-to-composite noise ratio) and CSO/CTB
(composite second order/composite triple beat) measurements.
5-1

CNR

Use the arrow keys to select and modify the fields on the left. First choose a channel to measure.
Noise measurement bandwidth for various TV standards
Typically, CCN measurements require that system engineers first measure the video carrier level (where the
sync tip of the modulation is the absolute peak level); then remove the video modulation by shutting down
the modulator - or simply remove the modulation from the carrier – to allow accurate noise measurement.
Unfortunately, removing the modulation interrupts service.
A better way to measure CCN accurately is to perform an in-service "gated" measurement, with the help
of gating technology and quiet line insertion in the vertical blanking interval of video signals that are off the
viewable screen (usually below line 12). If you choose a higher VITS line, you may start encountering video
modulation, and thus visible interference on the television picture.
In a gated CCN test, the S7200 will first measure peak carrier level, and then trigger on the appropriate VITS
line # (preset for each channel; can be set in the channel plan editor) to measure noise. Occasionally, VITS
lines are already quiet enough when video signals are delivered by the Broadcaster. It is highly
recommended to use your own VITS inserter to remove any measurement uncertainty.
Many other types of test signals may be inserted for gated mode testing, including in-channel frequency
response, differential gain, and differential phase. A quiet line is absolutely required for measuring CCN,
CSO, CTB, or cross-modulation. The S7200 is equipped with triggering technology that accurately locks onto
a specific VITS line and provides precise measurement results.
40
Standard I
Video bandwidth 6.75
Noise bandwidth 5.08
Before measuring CCN Ratio with your S7200 analyzer,
visit the channel plan editor (see Chapter 3: Channel
Plans) to set up the video carrier frequency and noise
bandwidth correction as necessary for your test.
The noise bandwidth may differ depending on the
channel bandwidth, which varies by location: NA, EU,
or another region. For example, the NTSC-M system
used in North America, as specified by the FCC,
employs a 4MHz noise bandwidth correction; while
PAL-D systems use a 5.75MHz noise correction.
B, G K1, L D, K
5.75 7.25 6.75
4.75 5.58 5.75
M, N
4.95
4.00