User Manual - TRS-RenTelco

Option VGA Detailed Measurement Information
Figure 3- 3: Frequency response with 500 MHz filter for Noise In Ratio measurement
Signal Source
The test signal used for the Noise Injection Ratio measurement is Full White,
which is located on the Test Signal Files CD-ROM.
If you plan to take only Noise Inj Ratio measurements, use a Full White Full
Field test pattern. Select the bitmap file that matches the format and refresh rate
of the test. For example, use the 640x480 -FullWhite.bmp file to test a 640x480
resolution format.
You can also use a Matrix signal as a test signal. For more information on the
Matrix signal refer to page 2 -16. For example, use the 640x480 -Matrix.bmp file
to test a 640x480 resolution format.
Interpreting Results
When the injection ratio is below a certain threshold, noise will not be perceived.
With the injection ratio greater than the threshold, perceived image quality is
degraded as a function of noise injection ratio. Noise Injection Ratio in dB is less
negative when the noise amplitude increases.
How Results are
Calculated
Using a Full White signal, the peak-to-peak fluctuation in luminance voltage (of
at least 100,000 samples) is measured. The noise amplitude is measured with
reference to oscilloscope ground. The Noise Injection Ratio measurement uses
the video wide bandwidth signal path of the MIU. The maximum value of the
fluctuation is used for computing the Noise Injection Ratio as shown in the
Figure 3 -4.
VM5000 Automatic Video Measurement Set User Manual 3-51