References :
1. Walter Fischer Presentation, Analog Television,
Definition : Noise = Interferer, Interferer on a Video Signal
Noise Measurements consists of :
• Luminance noise
o Luminance noise unweighted
o Luminance noise weighted
• Intermodulation
• Quantization noise
• Chrominance noise
• Hum
• White noise
• Triangular noise
2. PAL Systems Television Measurements, Tektronix®, February 2000
Definition : Noise refers to the fluctuations that are present in any electrical system. Noise can be either random or coherent and comes from a variety of natural and man made sources. Although there is always some noise present, an excessive amount is undesirable since it tends to degrade or obscure the signal of interest. Signal amplitudes do not always remain constant as the video signal is processed and transmitted. An absolute measurement of noise is therefore not particularly relevant as a certain amount of noise will have very different effects on signals of different amplitudes. Since it is the amount of noise relative to the signal amplitude rather than the absolute amount of noise that tends to cause problems, measurements of signal-to-noise ratios, expressed in dB, are made.
3. VM700T Data Sheet, Tektronix®,
Side notes 1. Source from PAL Systems Television Measurements, Tektronix®, February 2000
The electrical fluctuations that we refer to as noise form a very complex signal that does not lend itself to straightforward amplitude measurements. A number of special techniques have therefore been developed for measuring noise. A comprehensive discussion of noise measurement is outside the scope of this brief article. However, some of the methods which apply to television systems are discussed in this section. Special filters are generally required for noise measurements. These filters are used to separate the noise into its various frequency components for analysis. Each measurement standard typically calls for three or four measurements made with various combinations of the filters. Note that specifications for the filters vary from standard to standard.
The tangential method of noise measurement, useful for making operational measurements of random noise, is the only method discussed in detail in this article. While not the most accurate technique, the tangential measurement can provide a quick way of keeping track of system noise performance over time. Tangential noise measurements are made with a specially equipped waveform monitor. This feature is standard in the 1781R. Specialized equipment is required to completely characterize the noise performance of a system. Until recently, these capabilities were available only in dedicated noise measurement instruments. The VM700T, however, makes highly accurate noise measurements using filters implemented in software. The noise measurement features of the VM700T are reviewed briefly in this article.
PICTURE EFFECTS
Noisy pictures often appear grainy or snowy and sparkles of colour may be noticeable. Extremely noisy signals may be difficult for equipment to synchronize to and the picture may suffer from blurriness and a general lack of resolution.
TEST SIGNALS
The *tangential method can be used on any video signal with a constant luminance level without chrominance. The measurement can be made on a single line in the vertical interval although full field measurements are more accurate and somewhat easier to make. Any line with a constant pedestal level can be used to make VM700T Noise Spectrum measurements. A quiet line in the vertical interval is typically used (see Figure 6).
The VM700T Chrominance AM/PM noise measurement requires a red field test signal (see Figure 1).
Figure 1 : A red field test signal used to measure Chrominance AM/PM Noise
MEASUREMENT METHODS
*Tangential Method.
Tangential noise measurements can be made with a 1781R. The method is accurate to within 1 or 2 dB, down to noise levels of about 60 dB. Filters can be inserted in the AUX OUT/AUX IN path to separate noise components of different frequencies.
Noise Measurements consists of :
• Signal to Noise
Signal to Noise Ratio
WFM1781R and WFM1481 Measurement
Make sure the waveform monitor filter selection is set to FLAT(unless using the auxiliary filter capability) and the DC restorer to OFF or FAST. Select NOISE in the 1781R MEASURE menu.
(In the 1481, use the WAVEFORM COMPARISON mode to split the luminance level of interest in half and overlay the two parts). The measurement is made by adjusting the separation between the two traces until the dark area between them just disappears. When there is no perceptible dip in brightness between the two traces, the calibrated offset level (in dB) is the amount of noise. In the 1781R, the large knob is used to control the offset and the on screen readout provides the dB reading. In the 1481, the offset function is performed by the two dB NOISE controls in the lower right-hand corner. The dB reading is obtained from the knob settings.
Figure 2 : The 1781R tangential noise measurement mode showing excessive
trace separation. 
Figure 3 : The 1781R tangential noise measurement mode with trace separation
properly adjusted. This signal has a signal-to-noise ratio of 30 dB.
VM700T Automatic Measurement.
Select NOISE SPECTRUM in the VM700T MEASURE menu to make signal-to-noise measurements. A spectral display and numeric results are provided in this mode (see Figure 4). 
Figure 4 : The VM700T Noise Spectrum Display
Several lowpass, highpass, and weighting filters are available in this mode. Measurement standards typically require three or four measurements made with various combinations of these filters.The rms signal-to-noise ratio of the entire spectrum is always displayed in the upper right hand corner of the display. The threshold for dB rms are expected to meet typical recommended results as follows:
Noise unweighted, <-55dB rms Noise weighted, <-62 dB rms A cursor can be used to select a certain frequency for a peak-to peak noise measurement. The cursors can also be used to define a narrow range of frequencies for S/N measurements. The CHROMINANCE AM/PM selection in the VM700T MEASURE mode, which requires a red field test signal, provides information about the noise that affects the chrominance portion of the signal. Since the chrominance signal is sensitive to both amplitude (AM) and phase (PM) components of noise, two separate measurements are provided. A selection of filters is available in this mode. Noise measurements are also available in the VM700T AUTO mode. Quiet Lines. "Quiet lines" in the vertical interval are sometimes used to evaluate the amount of noise introduced in a certain part of the transmission path. A line is reinserted (and is therefore relatively noise free) at the transmitting end of the path of interest. This ensures that any noise measured on that line at the receiving end was introduced in that part of the path. 
Figure 5 : The VM700T Chrominance AM PM display . gambar6 Figure 6 : Black "Quiet" line for noise measurement.
Figure 6 : Black “Quiet” line for noise measurement
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