This standard specifies the measurement methods for television transmissions via orbiting satellites. This standard applies to the measurement of black-and-white and color television transmissions. These measurements are a supplement to the baseband measurement items used for telephone and television in Section 4 of Part 1 of this series of standards, "Baseband Measurements". For example, group delay/frequency characteristics and amplitude/frequency characteristics measurements. For measurement waveforms applicable to various current television systems, see the references listed in Chapter 9. GB/T 11299.14-1989 Satellite communication earth station radio equipment measurement methods Part 3: Subsystem combined measurements Section 4: Black-and-white and color television transmission measurements GB/T11299.14-1989 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Methods of measurement for radio equipment used in satellite earth stationsPart 3: Methods of measurements foncombination of suh-systems
Section Four-Measurements for monochromeand colour television transmissionThis standard is one of the standards in the series of "Methods of measurements for radio equipment used in satellite earth stations for satellite communication". 1 Subject content and scope of application
GB11299.14-89
This standard specifies the measurement methods for television transmission via orbiting satellites. This standard is applicable to the measurement of black-and-white and color television transmission. These measurements are a supplement to the baseband measurement items used for telephone and television in Section 4 "Baseband measurements" of Part 1 of this series of standards. For example, group delay/frequency characteristics and amplitude/frequency characteristics measurements. For the test waveforms applicable to various television systems in China, see the references listed in Chapter 9. 2 Introduction
Commercial test equipment may be used, but its performance should be sufficient to perform the tests described. For example, an oscilloscope should exhibit a flat frequency response and good return loss (e.g., 30 dB) at least over the nominal upper frequency range of the video baseband. Time and voltage calibration and display linearity are also important factors, and it is sometimes difficult to measure the amplitude waveform displayed on the screen with the necessary accuracy. When an accuracy of (.1B3) is required, the coordinate scale of the screen is unlikely to provide the required accuracy, which is usually necessary when measuring the true pulse tip. The use of a calibrator as described in Appendix A (Supplement) can help solve this problem and can also save time when making multiple measurements.
The various test waveforms involved in this standard are superimposed on a standard horizontal synchronization pulse!. The commercial signal generators generally used to provide these waveforms usually have little distortion and can be used directly without calibration. If this is not the case, or when the accuracy required for the measurement is comparable to the accuracy of the test equipment itself, the test results should be expressed based on the measurement equipment. Appropriate correction should be made for the distortion of the equipment. 3 Test signal level
Unless otherwise specified, the test signal required by this standard should be applied to the input of the system under test at the nominal level and at a level 3dB higher than the nominal level. The nominal input level of the system under test is the level that produces the nominal frequency deviation (see Reference 1). 4 Signal polarity and DC component
4.1 Definition and general considerations
The definition of a positive polarity video signal is: as the brightness signal voltage increases, the image changes from black to white. Approved by the Ministry of Electronics Industry of the People's Republic of China on March 1, 1989 144
Implementation on January 1, 1990
GB 11299.14--89
The useful DC component is related to the average brightness of the image. The useful DC component may or may not be included in the signal, so it does not need to be transmitted or output. If a pre-emphasis network is used, the image signal will not contain useful DC components. If a direct-coupled baseband amplifier is used, useless DC components may appear in the signal, so it is necessary to specify the limit value of this DC component under terminated and non-terminated conditions.
4.2 Baseband measurement method
The measurement equipment configuration is shown in Figure 1. A waveform generator that can generate a synchronization pulse of a specified amplitude based on the blanking level is connected to the baseband input of the system under test. An oscilloscope is connected to the output of the system under test, and the relative changes in the amplitude and/or polarity of the synchronization pulse based on the blanking level can be measured.
4.3 Result Expression
The signal polarity and the voltage of the useful and unwanted DC components shall be given. 4.4 Details to be Specified
When this measurement is required, the equipment specifications shall include the following: Required video signal polarity;
The voltage of the useful DC component:
C. Maximum voltage of the unwanted DC component allowed. 5 Insertion Gain
5.1 Definition
The insertion gain is defined as the ratio of the peak-to-peak amplitude of the specified test signal at the receiving end to the peak-to-peak amplitude of the signal at the transmitting end, expressed in decibels.
The peak-to-peak amplitude is defined as the difference in amplitude measured at two specified points on a test signal. 5.2 Measurement Method
The measurement equipment is configured as shown in Figure 1. Signal B in Figure 10 is applied to the input of the system under test. The luminance signal amplitude is defined as the distance between the center of the bar signal and the center of the blanking level. Note: If the equipment under test uses a positioning circuit, it should be removed because it affects the test accuracy. 5.3 Expression of results
The insertion gain is expressed in decibels.
5.4 Details to be specified
When this measurement is required, the equipment specifications shall include the following: a. The required insertion gain;
b. The insertion gain tolerance.
6 Noise
For measurement purposes, the noise of television systems can be divided into three categories: periodic noise, continuous random noise, and impulse noise. 6.1 Measurement method of periodic noise
The measurement equipment is configured as shown in Figure 2. Terminals (b) and (c) are used for time domain and frequency domain measurements respectively. The video input terminal of the device under test should be terminated with a load with the same characteristic impedance as its own. The periodic noise is measured in two frequency bands (see Reference 3), the first from 10kHz to the upper frequency limit of the video passband, and the second below 10kHz. The nature of the periodic noise depends on its source. To ensure that the nature of the noise observed can be adequately determined, measurements must be made in both the time and frequency domains. Time domain measurements require a wideband oscilloscope and suitable band-limiting filters. Frequency domain measurements of noise require a frequency-selective level meter whose tuning range should be sufficient to cover the required frequency band. Such measuring instruments are usually scaled in power, and the measured level values ​​are usually converted to peak-to-peak voltages with sufficient accuracy by adding 9 dB. For color television, it must be ensured that frequency components of periodic noise above the upper limit of the video band do not produce beat frequencies within the video band with the color subcarrier and/or continuous-conductor signal (if used). This effect can be checked by adding a color subcarrier sine wave signal with a peak-to-peak amplitude equal to the nominal luminance peak-to-peak value and then searching the entire playback frequency band (except for a small section around the color subcarrier frequency) with a narrowband frequency-selective level meter. In order to avoid possible overload of the measuring instrument, a narrowband band-stop filter tuned to the color subcarrier frequency must be inserted between the system under test and the measuring instrument. At this time, the insertion loss of the filter should be considered and the result should be corrected accordingly.
To verify that the measured periodic noise component is an intermodulation product, the color subcarrier and/or continuous pilot signal (if used) can be temporarily removed. At this time, the harmful component should disappear. When any intermodulation component appears in the video passband, its level should not be greater than the value allowed by the equipment technical conditions.
Note: ① Unless there are special restrictions, the level of the continuous baseband component presented outside the video passband can be much greater than the allowed level of the in-band component. Out-of-band signals may also be useful signals. For example, the audio subcarrier. In this case, when measuring periodic noise, all subcarriers transmitted by the system should simultaneously present the correct level.
②When the amplitude of the measured periodic signal is not significantly different from the amplitude of the random noise, it should be noted. In order to be able to distinguish these low-level signals when measuring, an oscilloscope is required whose time base is synchronized with the noisy low-level signals. 6.2 Method for measuring continuous random noise
The measurement equipment is configured as shown in Figure 2, and the measurement is made at end (a). When measuring continuous random noise at a point where the luminance signal level is known, an appropriate band-limiting filter must be used. The filter is used to filter out noise at the upper limit of the high-frequency video band (Figure 3) and below about 10kHz (Figure 4). Considering the effect of the noise distribution that varies with frequency, a noise weighting network is usually used to take into account the reduced sensitivity of the human eye to noise at the high end of the video band (see Figure 5). A broadband RMS meter should be used to measure noise in the frequency band above 10kHz2. It is important to ensure that only continuous random noise is present. If both continuous random noise and periodic or impulse noise are present, the result obtained from the RMS meter may not represent the true value of the random noise. An oscilloscope can be used to observe whether other noise components exist, and if necessary, their levels should be appropriately reduced before measuring the random noise.
Because the noise in the frequency band below 10kHz is generally periodic noise generated by the power supply, it is not necessary to measure continuous random noise in this range.
6.3 Measurement method of impulse noise
The measurement equipment is configured as shown in Figure 2. The measurement is carried out at the (d) end. The peak-to-peak amplitude of non-periodic or occasional impulse noise is measured using an oscilloscope.
Note: It is more advantageous to use a storage oscilloscope.
6.4 Result presentation
The measurement results should be given in tabular form, and the test conditions for various results should be given. 6.4.1 Periodic noise
The results should be expressed as the ratio (dB) of the peak-to-peak amplitude of the luminance signal to the peak-to-peak amplitude of the periodic noise. When a periodic noise component is identified, its level and frequency or repetition rate should be recorded according to Table 1. Table 1
Frequency or repetition rate
6.4.2 Continuous random noise
Level relative to luminance signal, dB
The result should be expressed as the ratio of the peak-to-peak value of the luminance signal to the weighted RMS value of the noise (references 2 and 5) (dB). The conditions are shown in Table 2.
Relative RF
Input level of the receiver1, dB
GB 11299. 14--89
Signal/noise ratio, dB
Video band weighting2
Chroma band weighting (see reference 3)
Note: 1) The numbers given in the table are only examples. According to the corresponding equipment technical conditions, 0 dB corresponds to the nominal RF input level of the receiver. 2) Normally, this measurement is required only when the noise power per unit bandwidth at 5 MHz exceeds the noise power per unit bandwidth at 1 MHz by approximately 11 dB (see Reference 5). The weighting network used for the measurement is shown in Figure 6. 6.4.3 Impulse noise
It should be stated whether this noise is observed and, if so, its duration, level and approximate waveform should be given. 6.5 Details to be specified
When this measurement is required, the equipment specifications should include the following: a.
Bandwidth used for noise measurement;
Weighting characteristics used;
Permissible continuous random noise level;
Permissible periodic noise level;
Permissible impulse noise level.
7 Linear waveform distortion
The linear waveform distortion of an ideal system is independent of the level of the applied signal within the normal operating range. From the perspective of the video signal waveform and its display effect on the image, the impairment caused by linear distortion can be described by four different time scales, corresponding to the duration of multiple fields, one field, one line and one pixel. When considering one of the time scales, this measurement method does not consider the other three corresponding impairments. Linear waveform distortion is caused by many different reasons. In order to fully evaluate its impact on the system, a variety of controllability tests must be performed. 7.1 Long-term waveform distortion
7.1.1 Definition and general considerations
Long-term waveform distortion is the difference between the linear response of the system under test and the linear response of a single-resistance-capacitance circuit with a time constant of multiple field times.
If a television test signal is applied to the input of the system under test, which simulates a change from a low average picture level (APL) to a high average picture level or from a high average picture level to a low average picture level, when the blanking level of the output signal does not accurately follow the blanking level of the input signal, a long-term waveform distortion is generated, the result of which is an exponential change in the waveform or a very low frequency damped oscillation superimposed on the signal. The peak amplitude of this oscillation overshoot and the time required for the oscillation to decay to a specified value should be measured. 7.1.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
Measurement is made using a signal that switches between two states of average picture level (12.5% ​​and 87.5%) (Figure 7). The time interval between the switching is long enough so that the transient has decayed to a negligible value before the next switching. The maximum overshoot of the signal envelope over its final steady-state value (X in Figure 8) is measured on a DC-coupled oscilloscope that does not itself have such distortion. The final value (X in Figure 8) is also measured. The measurement can be made by displaying a photograph of the waveform or by using a storage oscilloscope. If the overshoot caused by the transition from low average picture level to high average picture level is not equal to the overshoot caused by the reverse transition, the larger value should be taken as the measurement result.
7.1.3 Result presentation
GB11299.14--89
The measurement result should be expressed as the maximum overshoot value of Y% of the luminance signal amplitude and the decay time defined in the equipment specifications! () It is best to give a photograph of the oscilloscope display waveform. 7.1.4 Details to be specified
When this measurement is required, the equipment specifications should include the following: a. The maximum percentage of overshoot allowed (for example, X, -20%);. The decay time t required to reach and remain below a given height amplitude percentage X (for example, t=5 when reaching 3%) 7.2 Field time waveform distortion
7.2.! Meaning and general considerations
Field time waveform head is defined as: when a square wave signal with the same duration as the field time and the amplitude of the nominal value of the brightness signal is added to the input of the measured system, the change in the shape of the top of the square wave at the output end. This measurement does not include the duration of several lines at the beginning and end of the square wave.
7.2.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
Add a square wave signal as shown in Figure 9 to the input of the measured system, check the waveform at the output end with a DC coupled oscilloscope, measure the maximum deviation of the top level of the square wave signal relative to the center level of the square wave signal, and express it as a percentage of the amplitude of the square wave signal. When measuring, 250μs (about four lines) at the beginning and end of the square wave signal are ignored. 7.2.3 Result representation
The result is expressed as: the field time distortion does not exceed X% of the amplitude measured at the midpoint of the square wave signal. A waveform photo is attached. 7.2.4 Details to be specified
When this measurement is required, the following shall be included in the equipment specifications: 8. Repetition rate of the square wave signal (e.g. 50 Hz or 60 Hz); b. Permissible distortion percentage.
7.3 Line time waveform distortion
7.3.1 Definition and general considerations
Line time waveform distortion is defined as the change in the shape of the top of a bar signal observed at the output when a bar signal with a duration of the same magnitude as a line time and an amplitude equal to the nominal value of the luminance signal is added to the input of the system under test. This measurement does not include the duration of the start and end of the bar signal, which is equivalent to a few pixels.
7.3.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
The measurement method is similar to the measurement method of 7.2.2 bar time waveform distortion, except that the bar signal B. in Figure 10 is used as the test waveform. The same principles and protection measures are used during the measurement, and the 1us at the start and end are ignored. 7.3.3 Result Expression
Result expression is the same as that in 7.2.3. ． ．
7.3.4 Details to be Specified
When this measurement is required, the following shall be included in the equipment specifications:. Width of the signal;
b. Permissible distortion percentage.
7.4 Short-time waveform distortion
7.4.1 Definition
Short-time waveform distortion is defined as: when a short pulse or fast step signal with a specified amplitude and shape is added to the input of the system under test, the output pulse (or step) deviates from the original shape. 7.4.2 Measurement Method
The measurement equipment is configured as shown in Figure 1.
GB 11299. 14 --- 89
The test signal used consists of waveforms B, and B in Figure 10. These two waveforms are input and two distortion measurements are made. The first: - the pulse amplitude 5 is expressed as a percentage of the center hat degree of the row signal 2.Second, the amplitude of the leading edge or trailing edge of pulse B or bar signal B (\ringing") is shown as a percentage of the central amplitude of the received pulse or bar signal. The half width of pulse B in FIG10 is 2T (200ns) or T (100ns). The measurement of the ratio of pulse to bar signal can be repeated by using pulse B
with a half width of T (100rs) for 525 lines. Short-time waveform distortion can be measured with a step function signal. In this case, the system signal 13 in FIG10 is used to adjust the response waveform to the shape of FIG11 on an oscilloscope with a suitable frame, and the center point M on the midpoint grid where the black level transitions to the white level 50% coincides, and the black level and the white level coincide with the α segment and the β segment respectively. After the oscilloscope time base is properly adjusted, the transition of the slice wave from black to white can be measured. The time taken by the transition edge to rise from 10% to 90% of the peak value of the white level.
The amplitude of the undershoot and overshoot generated at the white level and the white level is measured together with the degree and duration of any oscillation occurring at these two levels.
7.4.3 Result Representation
The result should be expressed as follows:
&.2T pulse amplitude expressed as a percentage of the mid-point amplitude of the bar signal; b. The amplitude of the "ringing" and the position of its peaks in time relative to the maximum amplitude point of the B pulse: c. The amplitude of the T pulse is expressed as a percentage of the mid-point amplitude of the bar signal. Provide a photo of the above waveform at the same time.
The test results of the step signal should have a photo reflecting whether it meets the measurement frame. Also indicate: the measured rise time; ||tt| |The maximum amplitude of the overshoot;
The frequency of the "ringing";
d. The time interval during which the "ringing" amplitude exceeds the measurement grid range. 7.4.4 Details to be specified
When this measurement is required, the equipment specifications should include the following: the ratio of the 2T pulse and the T pulse to the midpoint amplitude of the bar signal, a.
The minimum frequency of the "ringing" allowed;
The amplitude of the raised portion allowed.
The test of the step signal should specify the following: a.
Output pulse rise time;
The overshoot amplitude allowed;
The minimum frequency of the "ringing" allowed.
7.5 Luminance/chromaticity inequality
7.5.1 Definition
7.5. 1.1 Gain inequality
Gain inequality is defined as the change in the amplitude of the chrominance component relative to the luminance component measured at the output when a test signal having specified luminance and chrominance components is applied to the input of the device under test (see Reference 2). 7.5.1.2 Delay inequality
Delay inequality is defined as the relative change in the time relationship of the corresponding parts of the luminance and chrominance components at the output when a specified composite test signal is applied to the input of the system under test. The composite test signal consists of a luminance signal with a fixed amplitude and time relationship to a chrominance subcarrier, which is modulated by the luminance signal. The composite signal is applied to the input of the circuit under test, and the modulation envelope of the luminance signal is compared to the chrominance signal at the output (see Reference 2). 7.5.2 General considerations
GB11299.14-89
The luminance/chrominance inequality is caused by the different gain/frequency response and envelope delay response to the chrominance and luminance signals of the baseband part of the television transmission system.
In the international standard color television system, the chrominance band and part of the luminance band are shared, so the amplitude and delay of the chrominance signal relative to the luminance signal must be specified. In actual measurement, the test signal must have both luminance band components and chrominance band components. 7.5.3 Measurement method
The measurement equipment is configured as shown in Figure 1.
A composite waveform as shown in Figure 12 is applied to the input of the system. The waveform is constructed by adding a sine square pulse signal with an amplitude of half the nominal luminance amplitude to a color subcarrier modulated 100% by such a sine square pulse. The peak-to-peak amplitude of the composite waveform is equal to the nominal luminance amplitude. Luma/chroma gain inequality appears on the displayed waveform as an upward or downward bend in the baseline relative to the blanking level. Delay inequality appears as a sinusoidal distortion of the baseline, and the peak-to-peak amplitude of the baseline distortion is proportional to the luminance/chroma delay inequality (see Figure 13). Use an oscilloscope with a vertical scale (10 to 100 scale units) and adjust the oscilloscope so that the pulse waveform can be accurately displayed in the range of 0 to 100. Measure the peak amplitude of the convexity or concave observed above or below the blanking level and record the Y and Y scales as shown in Figure 13. These two measurements are used to calculate the gain and delay inequality. If Y is expressed in linear units relative to a given reference level (such as blanking level). and Yb, adjust the gain of the oscilloscope so that the amplitude of the image signal (brightness plus chrominance) at the output of the system is relative to the same reference level and is set to 100 units. The gain inequality is: 2(Y. - Yh)
5×100%
100 + (Y. -Y,)
The delay inequality is:
yuan100
Where: T=
(i.e., for a 5MHz bandwidth, T=100ns); 2.f.
n—proportional to the half-width of the chrominance pulse (i.e., for a 10T pulse, n=10). Note: ① The delay obtained in formula (2) is an approximate value and applies regardless of whether n is an integer. (1)
② Can be measured using commercial equipment. The gain and delay inequality can be measured by adjusting the calibrated equalizer until the distortion displayed on the oscilloscope is offset. In this way, the oscilloscope acts only as a zero-point indicator. ③ When measuring the luminance/chrominance gain inequality in the presence of crosstalk (see 8.4), the additional distortion presented on the test waveform must be taken into account. ④ To measure the gain inequality, the amplitude of the line signal B2 of Figure 10 can also be compared with G, of the test waveform G of Figure 17, or with the peak-to-peak amplitude of the last step of G2. The relative amplitudes of B, and G in the original signal should be calculated for 525 lines. 7.5.4 Result Representation
7.5.4.1 Gain inequality
The luminance and chrominance gain inequality shall be expressed as a percentage of the luminance peak amplitude and shall be considered positive when the chrominance signal exceeds the luminance signal. 7.5.4.2 Delay inequality
The luminance and chrominance delay inequality shall be expressed in nanoseconds and shall be considered positive when the chrominance signal lags behind the luminance signal. 7.5.5 Details to be specified
When this measurement is required, the following should be included in the equipment specifications: a. Half-width of the pulse used;
b. Permissible gain inequality (±X%); c. Permissible delay inequality (±Yns). 8 Non-linear distortion
In long-distance television lines, the transmission characteristics are not completely linear. The degree of non-linear distortion produced depends on the average image voltage, the instantaneous amplitude of the luminance signal and the amplitude of the chrominance signal. 150
GB11299.14-89
In general, it is not meaningful to try to specify all non-linear characteristics in the transmission line. Therefore, the number of measurements must be limited to those items that are directly related to the image quality. In addition, the test conditions should be limited by systematically classifying the items to be measured in terms of definition.
Due to the waveform characteristics of the video signal, the nonlinearity of the circuit has different effects on the synchronization signal and the image signal, and the nonlinearity may affect the brightness and chrominance signals separately, or cause them to affect each other, which leads to the following classification of nonlinear distortion (see reference 2).
Non-linear distortion
Synchronization signal
Brightness signal
Amplitude distortion
Caused by the brightness signal
Amplitude
Caused by the chrominance signal
Amplitude
(Intermodulation)
Caused by the chrominance signal
Magnitude
Amplitude distortion
Picture signal
Chroma signal
Phase distortion
Caused by the chrominance signal
Amplitude
Caused by the brightness signal
Amplitude (Differential gain)
Caused by the brightness signal
Amplitude
(Differential phase)
The above classification applies to stable conditions where the stability time is long for the picture period. In this case, the concept of average picture level has a precise meaning. If these conditions are not met, for example if there is a sudden change in the DC component, additional nonlinear effects may occur, the extent of which depends on the very low frequency transient response of the line. 8.1 Luminance signal distortion
8.1.1 Definitions and general considerations
For a particular value of the average picture level, the nonlinear distortion of the luminance signal is defined as the deviation in the ratio between the amplitude of a small unit step input to the circuit under test and the corresponding amplitude of the circuit output when the step level changes from the blanking level to the white level. 8.1.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
The nonlinearity of luminance is measured using a staircase waveform D of Figure 14 or Figure 15, which is fed at levels of 0 dB and +3 dB relative to the nominal input level of the system, and the average picture levels are 12.5% ​​and 87.5%, which are formed by combining signal D with the signals providing maximum and minimum luminance, as shown in Figure 7.
The received waveform is passed through a differential shaping network, which converts the step signal into a 5-pulse train that approximates a sine square, see Figure 16. The pulse amplitudes are compared and the difference between their maximum and minimum values ​​is expressed as a percentage of the maximum value, thereby obtaining the distortion value. This measurement is performed at 12.5% ​​and 87.5% average picture levels. Figure 16 (a) is a suitable differential filter, and the component values ​​when the half-width is 1us are given in the figure. When the noise of the system is significant, the use of this filter helps to reduce the noise. The waveforms shown in Figures 16 (c) and (d) are examples. 8.1.3 Representation of results
The results should be expressed as: nonlinear distortion is X%. The values ​​of X corresponding to the 12.5% ​​and 87.5% average picture levels and the values ​​of X corresponding to the two input levels of the system should be given.
If necessary, a photo of the waveform displayed on the oscilloscope can be attached. 8.1.4 Details to be specified
GB 11299.14—89
When this measurement is required, the equipment technical requirements shall include the following: The allowable distortion values ​​when the average picture level is 12.5% ​​and 87.5% relative to the system nominal input level of 0dB and +3dB. 8.2 Chroma signal distortion
8.2.1 Definition
8.2.1.1 Amplitude distortion
Definition of non-linear distortion of chroma signal: For fixed values ​​of the amplitude of the card brightness signal and the average picture level, when the amplitude of the chroma subcarrier varies from a specified minimum value to a specified maximum value, the deviation in the ratio between the amplitude of the chroma subcarrier at the input of the circuit under test and the amplitude of the sample at the output of the circuit.
8.2.1.2 Phase distortion
The nonlinear phase distortion of the chroma subcarrier is defined as the change in the chroma subcarrier phase at the output of the circuit under test when the chroma subcarrier amplitude varies from a specified minimum value to a specified maximum value for fixed values ​​of the luminance subcarrier amplitude and the average picture level. 8.2.2 Measurement method
The measurement equipment is configured as shown in Figure 1. The chroma nonlinearity is measured using the superimposed three-level chroma signal (G or G.) shown in Figure 17. 8.2.2.1 Amplitude distortion
Substitute i=1 or i=3 in (3).
Where: A——-the amplitude of the received subcarrier; 100%
The pulse train position of the test signal G or G (1 is the minimum value; 3 is the maximum value); For a 625-line signal G
For a 525-line signal G
K,-2i—2.
The larger of the two percentages is taken as the amplitude distortion. When measuring, the gain of the chrominance channel is required to be within the specified range. The signal amplitude should be measured peak-to-peak, and a chrominance subcarrier bandpass filter should be used in the measurement. 8.2.2.2 Phase distortion
(3)
The measurement of phase distortion is to compare the phases of the three pulse trains in the received signals G and G, and take the largest phase difference (expressed in degrees). The phase of the smallest pulse train can be easily normalized using a vector oscilloscope. 8.2.3 Result representation
The result should be expressed as an amplitude distortion of X% and a phase distortion of Y degrees at the level of 0 dB and +3 dB relative to the nominal input level of the system. The values ​​of X and Y at the average image level of 12.5% ​​and 87.5% should be given. If necessary, a photo of the waveform displayed by the oscilloscope should be attached. 8.2.4 Details to be specified
When this measurement is required, the equipment specifications shall include the following: the permissible distortion values ​​for average picture levels of 12.5% ​​and 87.5% at 0 dB and +3 dB relative to the nominal system input level.
8.3 Synchronization signal distortion
There are two forms of synchronization signal distortion. The first is that which occurs with changes in picture level and lasts until the picture level is changed again. This is called sync signal static distortion. The second is that which occurs with changes in picture level and lasts for a short time. This is called sync signal transient distortion.
8.3.1 Static distortion bzxz.net
8.3.1.1 Definition and general considerations
The definition of synchronization signal static distortion is: for given average picture levels, the deviation of the mid-point amplitude of the sync pulse at the output from the nominal value.
GB 11299.14 --89
The insertion loss or gain of the circuit under test should be taken into account. The insertion gain is the ratio of the peak-to-peak value (blank level to white level) of the brightness component of the video signal at the output end of the system under test to the input end, expressed in decibels. 8.3.1, 2 Test method
The measurement equipment is configured as shown in the figure.
The static distortion of the synchronization signal is measured using the test signal of Figure 7, or a similar signal can be used. The signal should obtain the required average picture level of 12.5% ​​and 87.5% at a level of 0d3 + 3dB relative to the nominal input level of the system. Measure the amplitude between the midpoint of the synchronization pulse and the average blanking level (see Reference 2). The difference between the measured level and the nominal level represents the distortion generated.
8.3.1.3 Result Expression
The result shall be expressed as: The static distortion of the synchronization signal is X%, where X is the ratio of the difference between the measured value and the nominal value to the nominal value, expressed as a percentage. The X values ​​corresponding to the 12.5% ​​and 87.5% average image levels under two input level conditions shall be given. If the measured value is less than the nominal value, the X value is negative, i.e. compression; if the measured value is greater than the nominal value, the X value is positive, i.e. expansion. 8.3.1.4 Details to be Specified
When this measurement is required, the following shall be included in the equipment specifications: a. The maximum compression value allowed for each input level of the system under test; h. The maximum expansion value allowed for each input level of the system under test; c. The test signal used.
8.3.2 Transient distortion
8.3.2.1 Definition and general considerations
Transient distortion of synchronizing signals is defined as the maximum instantaneous deviation of the synchronizing pulses at the output of the system under test from the nominal midpoint amplitude when the mean picture level at the input varies between specified limits. If a sudden change in the mean picture level forms a DC step applied to the system under test, damped oscillations may occur due to various factors, such as any AC coupling, and also due to the time constant of any automatic frequency control circuit (see long-term waveform distortion). The signal may therefore enter the non-linear region of the transfer characteristic for a short period of time (e.g. the duration of a field). The distortion thus induced is transient and generally has no significant effect on the picture, but compression of the synchronizing pulses may cause the picture to lose sync. 8.3.2.2 Measurement method
The measuring equipment is shown in Figure 1.
This distortion is measured using the test signal of Figure 7 or a similar multiple that can switch the mean picture level from 12.5% ​​to 87.5%. The maximum instantaneous change in the amplitude of the sync pulse can be measured by changing the average picture level from 12.5% ​​to 87.5% and back to 12.5% ​​with a period of a few seconds. The transient time should be less than the line period.
Due to the instantaneous nature of this distortion, it can be measured using a photographic or storage oscilloscope. Regardless of which method is used, the waveform must be differentiated using a filter (see Figure 16(a)) before it is applied to the oscilloscope. In this way, the blanking level position displayed on the display is independent of the brightness level.
The oscilloscope time base is set to a slow speed (for example, 0.01 cm/s) and the Y gain is adjusted so that the indication of the differentiated sync pulse envelope on the oscilloscope is the same as the indication of the 1V peak-to-peak video signal before differentiation (for example, 100 units). The pulses generated by the differentiation of the image signal are not considered. When the average picture level changes, the displayed waveform is photographed and the maximum change in envelope height can be measured from the photograph (see Figure 18). This measurement is performed at levels of 0 dB and +3 dB relative to the nominal input level of the system. 8.3.2.3 Representation of results
The result should be expressed as: Transient distortion of sync signal is X%. Where X is the difference between the nominal value and the extreme value observed with the change of the average picture level, expressed as a percentage of the nominal value. The value of X corresponding to each input level of the system should be given. If necessary, a photograph showing the results should be provided.
8.3.2.4 Details to be specified
When this measurement is required, the following should be included in the equipment specifications: 1.53
a. Maximum allowed instantaneous compression value;
b. Maximum allowed instantaneous expansion value.
8.4 Crosstalk distortion of chrominance signal/luminance signal 8.4.1 Definition and general considerations
GB11299.14—89
Chroma/luminance signal crosstalk refers to the intermodulation formed by the chrominance signal entering the luminance signal. It is defined as: the change in the luminance signal level observed when the average picture level is a specific value and the chrominance signal is filtered out. 8.4.2 Measurement method
The measurement equipment configuration is shown in Figure 1.
Chroma/luminance crosstalk is measured using the G or G2 signal (Figure 17) superimposed on the 50% step of the B2 signal (Figure 10). After transmission through the system under test, when the subcarrier has the maximum amplitude, the incremental change in the amplitude of the step signal is measured and expressed as a fraction of the amplitude of signal B,. For ease of measurement, the subcarrier should be filtered out before the signal is added to the oscilloscope. This measurement is performed at levels of 0 dB and +3 dB for the nominal input level of the system. If the step level changes toward the white level, the crosstalk is expressed as a positive value; otherwise, it is a negative value. 8.4.3 Result Representation
The result should be expressed in a narrative manner, that is, the chroma/luminance crosstalk does not exceed X%, where X is the change in the amplitude of the step voltage increment relative to the amplitude of signal B, and the result can be positive or negative. 8.4.4 Details to be Specified
When this measurement is required, the equipment technical requirements should include the following: the allowable crosstalk value at each input level of the system. 8.5 Differential gain distortion
8.5.1 Definition and general considerations
Differential gain distortion of a television system refers to the change in the amplitude of the chrominance signal as the level of the luminance signal changes. It is defined as follows: A color subcarrier with a specified constant level is added to the luminance signal and sent to the input of the system under test. When the luminance signal changes from blanking level to white level and the average picture level remains at a certain value, the change in the color subcarrier amplitude at the output of the system under test is called differential gain distortion.
8.5.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
Measured with a rising 5-step staircase wave D? (see Figures 14 and 15), differential gain distortion is measured at levels of 0 dB and +3 dB relative to the nominal system input level, at 12.5% ​​and 87.5% average picture levels. In order to isolate the color subcarrier signal, a bandpass filter should be connected between the measuring oscilloscope and the output of the system under test for each measurement. In this way, the amplitude of the subcarrier on each step can be easily measured from the subcarrier envelope displayed by the oscilloscope. The selection of the filter bandwidth should achieve the best balance between the signal-to-noise ratio and the avoidance of transient characteristics when the step is switched. Because both factors will affect the measurement accuracy, a 1MHz bandwidth filter is commonly used in the 625-line system. The differential gain can be obtained by measuring the subcarrier amplitude at the blanking level and at the 1 to 5 steps in ascending order of the brightness level. The two values ​​of X% and Y% are used to represent the extreme values ​​(maximum and minimum) of the subcarrier amplitude on the step relative to the subcarrier amplitude at the blanking level.
The subcarrier amplitude at the blanking level is represented by A, and the subcarrier amplitude on the steps 1 to 5 is represented by A, to A in the ascending order of the brightness signal. After comparing the amplitudes of A. to As, the maximum difference exceeding A is represented by A. The percentage of A is expressed as follows: X = [4o:Am --1] × 100%
When A is the maximum value, X=0.
If there is a magnitude less than A, the difference between the minimum value and A is expressed as a percentage of A. That is: [(A,As)mm -- 1] × 100%
（4）
（5）
When A is the minimum value, Y=0.
The peak-to-peak value of differential gain distortion is:
IXI+ {YI=
GB11299.14—89
r(Ao,**,As)max (Ao,*.-,A,)inA
Note: If higher resolution is required, the waveform envelope of the filter output can be detected, so that the oscilloscope can observe the waveform with a higher gain. Otherwise, the oscilloscope gain will be limited by the higher subcarrier amplitude. 8.5.3 Result Expression
The measured value is expressed as a percentage of the subcarrier amplitude at the blanking level (X% and Y%) and filled in Table 3. Table 3
System input level
(relative to nominal value)
8.5.4 Details to be specified
Differential gain distortion
87.5% API.
When this measurement is required, the equipment specifications shall include the following:a. The differential gain distortion allowed for each average picture level value at the system nominal input level. Y%
The differential gain distortion allowed for each average picture level value when the system nominal input level is 3 dB. b.
8.6 Differential phase distortion
8.6.1 Definitions and general considerations
The differential phase distortion of a television system is the change in the phase of the chrominance signal as the level of the luminance signal changes. Its definition is: a color subcarrier with a specified constant amplitude is superimposed on the luminance signal and added to the input of the system under test. When the luminance signal changes from the blanking level to the white level, and the average image level remains at a specific value, the change in the color subcarrier phase at the system output is called differential phase distortion.
8.6.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
The measurement method and waveform used are similar to those used to measure differential gain distortion. The only difference is that the subcarrier phase (instead of the amplitude) is measured relative to the two extreme values ​​(positive and negative) of the subcarrier phase at the blanking level. These two values ​​are represented by X' and Y°. Therefore: X° = (Φ。,.*,Φ,)max —Φ(degrees)y°(Φ。,Φ,)min —。 (degrees)
(7)
Where.Φ。,…,@, are Φ at the blanking level. The subcarrier phase measured at each step of Φ, at the maximum brightness level, X and Y may be zero, and the peak-to-peak value of the differential phase distortion is:
iX[+|Y(Φ,,Φg)max -(Φ,,Φ,)min(degrees) Note: Measuring the phase angle of the subcarrier requires special test equipment, which has been commercialized. 8.6.3 Result expression
The measured value is expressed in degrees relative to the subcarrier phase at the blanking level (X° and Y\) and filled in Table 4.9)1 Definition and general considerations
Differential gain distortion of a television system refers to the change in the amplitude of the chrominance signal as the level of the luminance signal changes. It is defined as follows: A color subcarrier with a specified constant level is added to the luminance signal and sent to the input of the system under test. When the luminance signal changes from blanking level to white level and the average picture level remains at a certain value, the change in the amplitude of the color subcarrier at the output of the system under test is called differential gain distortion.
8.5.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
Measured with a rising 5-step waveform D? (see Figures 14 and 15), the differential gain distortion is measured at levels of 0 dB and +3 dB relative to the nominal input level of the system, at an average picture level of 12.5% ​​and 87.5%. In order to isolate the color subcarrier signal, a bandpass filter should be connected between the measuring oscilloscope and the output of the system under test for each measurement. In this way, the amplitude of the subcarrier on each step can be easily measured from the subcarrier envelope displayed by the oscilloscope. The selection of the filter bandwidth should achieve the best balance between the signal-to-noise ratio and the avoidance of transient characteristics when the step is switched. Because both factors will affect the measurement accuracy, a 1MHz bandwidth filter is commonly used in the 625-line system. The differential gain can be obtained by measuring the subcarrier amplitude at the blanking level and at the 1 to 5 steps in ascending order of the brightness level. The two values ​​of X% and Y% are used to represent the extreme values ​​(maximum and minimum) of the subcarrier amplitude on the step relative to the subcarrier amplitude at the blanking level.
The subcarrier amplitude at the blanking level is represented by A, and the subcarrier amplitude on the steps 1 to 5 is represented by A, to A in the ascending order of the brightness signal. After comparing the amplitudes of A. to As, the maximum difference exceeding A is represented by A. The percentage of A is expressed as follows: X = [4o:Am --1] × 100%
When A is the maximum value, X=0.
If there is a magnitude less than A, the difference between the minimum value and A is expressed as a percentage of A. That is: [(A,As)mm -- 1] × 100%
（4）
（5）
When A is the minimum value, Y=0.
The peak-to-peak value of differential gain distortion is:
IXI+ {YI=
GB11299.14—89
r(Ao,**,As)max (Ao,*.-,A,)inA
Note: If higher resolution is required, the waveform envelope of the filter output can be detected, so that the oscilloscope can observe the waveform with a higher gain. Otherwise, the oscilloscope gain will be limited by the higher subcarrier amplitude. 8.5.3 Result Expression
The measured value is expressed as a percentage of the subcarrier amplitude at the blanking level (X% and Y%) and filled in Table 3. Table 3
System input level
(relative to nominal value)
8.5.4 Details to be specified
Differential gain distortion
87.5% API.
When this measurement is required, the equipment specifications shall include the following:a. The differential gain distortion allowed for each average picture level value at the system nominal input level. Y%
The differential gain distortion allowed for each average picture level value when the system nominal input level is 3 dB. b.
8.6 Differential phase distortion
8.6.1 Definitions and general considerations
The differential phase distortion of a television system is the change in the phase of the chrominance signal as the level of the luminance signal changes. Its definition is: a color subcarrier with a specified constant amplitude is superimposed on the luminance signal and added to the input of the system under test. When the luminance signal changes from the blanking level to the white level, and the average image level remains at a specific value, the change in the color subcarrier phase at the system output is called differential phase distortion.
8.6.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
The measurement method and waveform used are similar to those used to measure differential gain distortion. The only difference is that the subcarrier phase (instead of the amplitude) is measured relative to the two extreme values ​​(positive and negative) of the subcarrier phase at the blanking level. These two values ​​are represented by X' and Y°. Therefore: X° = (Φ。,.*,Φ,)max —Φ(degrees)y°(Φ。,Φ,)min —。 (degrees)
(7)
Where.Φ。,…,@, are Φ at the blanking level. The subcarrier phase measured at each step of Φ, at the maximum brightness level, X and Y may be zero, and the peak-to-peak value of the differential phase distortion is:
iX[+|Y(Φ,,Φg)max -(Φ,,Φ,)min(degrees) Note: Measuring the phase angle of the subcarrier requires special test equipment, which has been commercialized. 8.6.3 Result expression
The measured value is expressed in degrees relative to the subcarrier phase at the blanking level (X° and Y\) and filled in Table 4.9)1 Definition and general considerations
Differential gain distortion of a television system refers to the change in the amplitude of the chrominance signal as the level of the luminance signal changes. It is defined as follows: A color subcarrier with a specified constant level is added to the luminance signal and sent to the input of the system under test. When the luminance signal changes from blanking level to white level and the average picture level remains at a certain value, the change in the amplitude of the color subcarrier at the output of the system under test is called differential gain distortion.
8.5.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
Measured with a rising 5-step waveform D? (see Figures 14 and 15), the differential gain distortion is measured at levels of 0 dB and +3 dB relative to the nominal input level of the system, at an average picture level of 12.5% ​​and 87.5%. In order to isolate the color subcarrier signal, a bandpass filter should be connected between the measuring oscilloscope and the output of the system under test for each measurement. In this way, the amplitude of the subcarrier on each step can be easily measured from the subcarrier envelope displayed by the oscilloscope. The selection of the filter bandwidth should achieve the best balance between the signal-to-noise ratio and the avoidance of transient characteristics when the step is switched. Because both factors will affect the measurement accuracy, a 1MHz bandwidth filter is commonly used in the 625-line system. The differential gain can be obtained by measuring the subcarrier amplitude at the blanking level and at the 1 to 5 steps in ascending order of the brightness level. The two values ​​of X% and Y% are used to represent the extreme values ​​(maximum and minimum) of the subcarrier amplitude on the step relative to the subcarrier amplitude at the blanking level.
The subcarrier amplitude at the blanking level is represented by A, and the subcarrier amplitude on the steps 1 to 5 is represented by A, to A in the ascending order of the brightness signal. After comparing the amplitudes of A. to As, the maximum difference exceeding A is represented by A. The percentage of A is expressed as follows: X = [4o:Am --1] × 100%
When A is the maximum value, X=0.
If there is a magnitude less than A, the difference between the minimum value and A is expressed as a percentage of A. That is: [(A,As)mm -- 1] × 100%
（4）
（5）
When A is the minimum value, Y=0.
The peak-to-peak value of differential gain distortion is:
IXI+ {YI=
GB11299.14—89
r(Ao,**,As)max (Ao,*.-,A,)inA
Note: If higher resolution is required, the waveform envelope of the filter output can be detected, so that the oscilloscope can observe the waveform with a higher gain. Otherwise, the oscilloscope gain will be limited by the higher subcarrier amplitude. 8.5.3 Result Expression
The measured value is expressed as a percentage of the subcarrier amplitude at the blanking level (X% and Y%) and filled in Table 3. Table 3
System input level
(relative to nominal value)
8.5.4 Details to be specified
Differential gain distortion
87.5% API.
When this measurement is required, the equipment specifications shall include the following:a. The differential gain distortion allowed for each average picture level value at the system nominal input level. Y%
The differential gain distortion allowed for each average picture level value when the system nominal input level is 3 dB. b.
8.6 Differential phase distortion
8.6.1 Definitions and general considerations
The differential phase distortion of a television system is the change in the phase of the chrominance signal as the level of the luminance signal changes. Its definition is: a color subcarrier with a specified constant amplitude is superimposed on the luminance signal and added to the input of the system under test. When the luminance signal changes from the blanking level to the white level, and the average image level remains at a specific value, the change in the color subcarrier phase at the system output is called differential phase distortion.
8.6.2 Measurement method
The measurement equipment is configured as shown in Figure 1.
The measurement method and waveform used are similar to those used to measure differential gain distortion. The only difference is that the subcarrier phase (instead of the amplitude) is measured relative to the two extreme values ​​(positive and negative) of the subcarrier phase at the blanking level. These two values ​​are represented by X' and Y°. Therefore: X° = (Φ。,.*,Φ,)max —Φ(degrees)y°(Φ。,Φ,)min —。 (degrees)
(7)
Where.Φ。,…,@, are Φ at the blanking level. The subcarrier phase measured at each step of Φ, at the maximum brightness level, X and Y may be zero, and the peak-to-peak value of the differential phase distortion is:
iX[+|Y(Φ,,Φg)max -(Φ,,Φ,)min(degrees) Note: Measuring the phase angle of the subcarrier requires special test equipment, which has been commercialized. 8.6.3 Result expression
The measured value is expressed in degrees relative to the subcarrier phase at the blanking level (X° and Y\) and filled in Table 4.9)2 Measurement method
The measurement equipment is configured as shown in Figure 1.
The measurement method and waveform used are similar to those used to measure differential gain distortion. The only difference is that the subcarrier phase (instead of the amplitude) is measured relative to the two extreme values ​​(positive and negative) of the subcarrier phase at the blanking level. These two values ​​are represented by X' and Y°. Therefore: X° = (Φ。,.*,Φ,)max —Φ(degrees)y°(Φ。,Φ,)min —。 (degrees)
(7)
Where.Φ。,…,@, are Φ from the blanking level. The subcarrier phase measured at each step of Φ, at the maximum brightness level, X and Y may be zero, and the peak-to-peak value of the differential phase distortion is:
iX[+|Y(Φ,,Φg)max -(Φ,,Φ,)min(degrees) Note: Measuring the phase angle of the subcarrier requires special test equipment, which has been commercialized. 8.6.3 Result expression
The measured value is expressed in degrees relative to the subcarrier phase at the blanking level (X° and Y\) and filled in Table 4.9)2 Measurement method
The measurement equipment is configured as shown in Figure 1.
The measurement method and waveform used are similar to those used to measure differential gain distortion. The only difference is that the subcarrier phase (instead of the amplitude) is measured relative to the two extreme values ​​(positive and negative) of the subcarrier phase at the blanking level. These two values ​​are represented by X' and Y°. Therefore: X° = (Φ。,.*,Φ,)max —Φ(degrees)y°(Φ。,Φ,)min —。 (degrees)
(7)
Where.Φ。,…,@, are Φ from the blanking level. The subcarrier phase measured at each step of Φ, at the maximum brightness level, X and Y may be zero, and the peak-to-peak value of the differential phase distortion is:
iX[+|Y(Φ,,Φg)max -(Φ,,Φ,)min(degrees) Note: Measuring the phase angle of the subcarrier requires special test equipment, which has been commercialized. 8.6.3 Result expression
The measured value is expressed in degrees relative to the subcarrier phase at the blanking level (X° and Y\) and filled in Table 4.9)
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