Some standard content:
UDC 621.397.23:621.317
National Standard of the People's Republic of China
GB3659—83
Methods of measurement of television video channel1983-05-05Promulgated
National Bureau of Standards
1984-13-01Implementation
National Standard of the People's Republic of China
Methods of measurement of television video channel
Methods of measurement of television video channelThis standard applies to black-and-white and color television video channels in my country. Note: Channel interfaces associated with international television video channels are not subject to this limitation. 1 Explanation of terms
1.1 TV video channel
UDC621.397.23
:621.317
GB3659-83
TV video channel refers to a channel or unit device, regardless of the signal processing process of its intermediate links, its input and output are full color TV signals or black and white TV signals. Note: When testing some equipment (such as signal source, transmitter, receiver, etc.) in accordance with the items specified in this standard, partial modifications and supplements can be made according to their special circumstances. 1.2 Full color TV signal
Full color TV signal is composed of brightness signal, chrominance signal, color synchronization signal and composite synchronization signal. 1.3 Average picture level (APL)
The definition of average picture level is: the average value of the average component of the image signal amplitude during the effective line in the entire frame period (excluding the line and field blanking period), and is expressed as a percentage of the nominal value of the brightness signal amplitude. 1.4 Special terms for waveforms (see Figure 1 and Table 1) T:
Figure 1 Full color television signal within a line periodApproved by the National Bureau of Standards on May 5, 1983
Implementation on April 1, 1984
Average image level
Instantaneous value of brightness signal amplitude
Project name
GB3659-83
Peak value of image signal amplitude (based on blanking level, its value can be positive or negative)Peak value of chrominance signal amplitude
Peak-to-peak value of full color television signal amplitude Difference between black level and blanking level
Peak-to-peak value of color burst signal amplitude
Nominal value of brightness signal amplitude
Peak-to-peak value of black-and-white full television signal amplitudeHorizontal synchronization signal amplitude
Horizontal synchronization signal width
Horizontal blanking signal width
Horizontal blanking signal front shoulder width
Horizontal blanking signal rear shoulder width
Horizontal validity period
Color burst signal start time
Color burst signal width
Note: All pulse widths are the widths between half-amplitude points. 2 Test signal
2.1 Field square wave signal A (see Figure 2)
ar-@mt
Note: This signal may also include field synchronization pulses when necessary. 2
Line sync ratio
Figure 2 Field square wave signal A
GB3659—83
2.22T sine square wave and bar pulse signal B1, B: (see Figure 3)&
Figure 32T sine square wave and bar pulse signal B1, B3 Note: ①Ba pulse edge establishment time is about 2T. 2.2x6×106=83.3ns
Where f. is the upper limit frequency of the nominal video bandwidth, f. 6MHz. 2.3 Multi-wave burst signal C (see Figure 4)
580mVc
2.4 Step wave signal D (see Figure 5)
12 16 4 24
Multi-wave burst signal C
(a) Average picture D1 when the image level is 50%
Tuune
GB3659—83
(b) D1 when the average picture level is 12.5%(c) D1 when the average picture level is 87.5%Figure 5 Step wave signal D1
2.5 Step wave superimposed on subcarrier signal D2 (see Figure 6).
Figure 6 Step wave superimposed on subcarrier signal D2
2.6 250kHz square wave signal E (see Figure 7)
Pulse formation timing is
Figure 7 250kHz square wave signal E
GB3659—83
2.7 10T signal F filled with subcarrier and bar pulse signal G filled with subcarrier (see Figure 8)Fum
Electric brush filling liquid
f = d.43MHz
Figure 8 Subcarrier filled 10T and bar pulse signal F, G2.810T modulated subcarrier signal F1 and bar pulse modulated subcarrier signal G1 (see Figure 9) is the disease pox (
Figure 910T and bar pulse modulated subcarrier signal F1, G15
2.9 Three-level chrominance signal G2 (see Figure 10) 70YrbzxZ.net
Note: ①bs is the brightness signal amplitude at the last part of G2. ②be is the brightness signal amplitude after G2 2.10 Flat-field signal K (see Figure 11)
GB3659—83
Three-level chrominance signal G2
Figure 11 Flat-field signal K
Note: ① Level u can be 0, 350 or 700mV according to the situation. ② Flat-field signal K is composed of the above equal amplitude signals during the effective line period of the whole field. 6
3 Test items and methods
GB3659—83
When performing the following tests, the test The test signal can be composed of various test signals specified above by appropriate methods. However, its average image level, unless otherwise specified, should be close to 50%. In addition, various tests (especially intervention gain) should be carried out when the tested channel is in the working state specified in the design.
3.1 Reflection loss
In the frequency domain, the impedance Z(f) at any frequency is the reflection loss relative to the nominal impedance Z. Zo+z(f)
p=201g
Z. -z (f)
The nominal value of the unbalanced impedance to ground of the television equipment or video channel as a unit at the interconnected input and output points shall be 752.
75+z(f)
p=201g-2（)9
In the time domain, the reflection loss is calculated by the following formula Ail
p=201g
Where: A1-
-The peak-to-peak value of the incident signal amplitude:
-The peak-to-peak value of the reflected signal amplitude.
Test method:
Frequency domain method--Measure within the specified frequency band using a reflection bridge and take the minimum value. Time domain method--Use the signal B in Figure 3, measure the peak-to-peak value of the incident signal and the reflected signal amplitude, and then calculate using the above formula. When the reflection loss is independent of frequency, the results measured by the two methods are quantitatively the same. When the results of the two methods are different, the frequency domain method shall prevail.
3.2 Intervention gain and its stability
3.2.1 Intervention gain
Definition: The ratio of the peak-to-peak value L of the signal amplitude at the output end of the measured channel to the nominal value Lo (700mV peak-to-peak) of the signal amplitude at the input end is called the intervention gain, and is expressed in dB. L
G=201g
Test method:
Add the bar pulse signal B3 of Figure 3 to the input end of the measured channel, measure the amplitude L between the midpoint 6 of the bar pulse signal and the blanking level 61 on the oscilloscope at the output end (Figure 12), and then calculate using the above formula. 12.5s
3.2.2 Dynamic intervention gain variation
GB3659—83
Definition: The amount by which the intervention gain changes when the average image level of the video signal is different is called dynamic intervention gain variation. Test method:
Using the intervention gain G50 when the average image level is 50% as the benchmark, measure the intervention gains G12.5 and G87.5 when the average image level is 12.5% and 87.5% to calculate the following variation values: 4G, = |G12.5—G60 l
4G2—|G87.5—G60l
The maximum value of 4G1 and 4G2 is the measured dynamic intervention gain variation. 3.2.3 Intervention gain stability
Definition: The maximum deviation value of the intervention gain within the specified time (short cycle 1 second and medium cycle 1 hour) represents the intervention gain stability. The long-term variation is specified by the equipment technical conditions. Test method:
Same as the intervention gain test method, and the test is performed according to the time specified in the definition. 3.3 Video clutter
3.3.1 Continuous random noise
Definition: The continuous random noise signal-to-noise ratio is the ratio of the nominal value of the brightness signal amplitude to the effective value of the random noise amplitude measured after bandwidth limitation, expressed in dB, and the calculation formula is: Nominal brightness signal amplitude in dB
S/N=201g
Effective value of random noise amplitude
The weighted random noise signal-to-noise ratio is the ratio of the nominal value of the brightness signal amplitude to the effective value of the random noise amplitude measured after passing through the specified weighting and bandwidth limitation network, expressed in dB, and the calculation formula is: Nominal value of the brightness signal amplitude
S/N (weighted)=201g
Effective value of the weighted random noise amplitude
Test method:
When the channel under test has a clamping circuit, the flat field signal K shown in Figure 11 is sent at the input end. When the channel under test has no clamping circuit, no signal is required.
To measure random noise, an instrument that reads the effective value of the amplitude is required. For power measurement, the measurement must have an effective time constant or integration time of about 1 second.
Between the object being measured and the measuring instrument, a band-limiting filter should be connected. When testing black-and-white TV channels, a 10kHz high-pass filter (see Appendix A.2) should be used to limit the lower limit of the frequency band to eliminate the influence of AC interference and microphonic effects. A low-pass filter with the nominal bandwidth of the video channel (see Appendix A, 1) should be used to limit the upper limit of the frequency band to exclude noise outside the video band. When testing color TV channels, in order to eliminate subcarrier components from random noise, a subcarrier notch should be connected in addition to high-pass and low-pass filters. When testing the weighted signal-to-noise ratio, a unified weighting network should be connected in front of the test instrument (see national standard GB3660-83 "Uniform weighting network for measuring continuous random noise in video").
3.3.2 Power supply interference
Definition: The power supply signal-to-noise ratio is the ratio of the nominal value of the brightness signal amplitude to the peak-to-peak value of the noise amplitude from the AC power supply within 1Hz, expressed in dB, and the calculation formula is: Test method:
Nominal value of the brightness signal amplitude dB
S/N=201g peak-to-peak value of the wave amplitude
Use a video noise tester, put the instrument in the working state when it is connected to a 1kHz low-pass filter (see Appendix A.3), measure the peak-to-peak value of the noise amplitude, and calculate it or read it directly from the instrument. 3.3.3 Single-frequency interference
GB3659-83
Definition: The signal-to-noise ratio of single-frequency interference is the ratio of the nominal value of the brightness signal amplitude to the peak-to-peak value of each single-frequency clutter amplitude within the nominal video bandwidth from 1kHz to 6MHz, expressed in dB, and the calculation formula is: Nominal value of brightness signal amplitude
S/N=201g Peak-to-peak value of single-frequency clutter amplitude de
Test method:
Measure using an oscilloscope method or a frequency selection method. When there are multiple single-frequency interferences, take the one with the largest amplitude among the clutter for calculation. 3.3.4 Pulse Interference
Definition: The pulse noise signal-to-noise ratio is the ratio of the nominal value of the brightness signal amplitude to the peak-to-peak value of the pulse noise amplitude, expressed in dB, and the calculation formula is:
Nominal value of the brightness signal amplitude
S/N=201gPeak-to-peak value of the pulse soft wave amplitude dE
Test method:
Use an oscilloscope to measure the peak-to-peak value of the pulse noise amplitude at the output end of the channel under test and then calculate. 3.3.5 Crosstalk (referring to crosstalk from other TV channels) Definition: The crosstalk signal-to-noise ratio is the ratio of the nominal value of the brightness signal amplitude to the peak-to-peak value of the crosstalk amplitude of the measured channel, expressed in dB, and its calculation formula is:
Test method:
Nominal value of brightness signal amplitude dB
S/N=201g
Peak-to-peak value of crosstalk amplitude
Crosstalk noise is generally related to the transmission signal in the crosstalked channel. Therefore, it should be measured in two cases: with or without a signal in the crosstalked channel.
When the interference in the crosstalked channel is basically similar to the test signal of the interfering channel (only the amplitude is different), the B1 and B: signals in Figure 3 are used; when the interference in the crosstalked channel is deformed by differentiation or the interference voltage is proportional to the frequency, the test signal uses the 10T and bar pulse signals F and G filled with subcarriers (see Figure 8). Use a high-sensitivity oscilloscope or other instrument to measure the peak-to-peak value of the crosstalk wave amplitude at the output end of the measured channel, and then calculate it.
3.4 Video nonlinear distortion
The degree of nonlinear distortion is mainly related to the average image level, the instantaneous value of the brightness signal amplitude, and the amplitude of the chrominance signal. Therefore, the following indicators are measured at three different average image levels (12.5%, 50%, and 87.5%), and the maximum one is taken. 3.4.1 Brightness nonlinear distortion
Definition: When the average image level is a certain value, a small-amplitude step signal with a starting level gradually increasing from the blanking level to the white level is added to the input end of the measured channel. The maximum difference between the ratio of each step amplitude at the output end to the corresponding step amplitude at the input end is called brightness signal nonlinear distortion.
Test method:
Use the step wave signal D of three average image levels in Figure 5 and send it to the input end of the channel under test. The output passes through a differential and forming network (see Appendix A.4) to convert the signal into a series of five sharp pulses (Figure 13). Calculate the ratio of the difference between the maximum value Amx and the minimum value Amn of the pulse amplitude to its maximum value, expressed as a percentage. The calculation formula is: Brightness nonlinear distortion D = 4m = 4×100%
3.4.2 Intermodulation distortion of chrominance signal to brightness signal GB3659-83
Definition: When a chrominance signal of a specified amplitude is superimposed on a brightness signal of a constant amplitude and added to the input end of the channel under test, and the average image level is maintained at a certain specific value, the change in the brightness signal amplitude caused by the superimposed chrominance signal at the output end is called intermodulation distortion of the chrominance signal to the brightness signal.
Test method:
Add the signal of Figure 9 or Figure 10 to the input of the channel under test. At the output, after suppressing the subcarrier, measure the amplitude of the luminance signal at G1 (or at the last part of G2) (bs in Figure 14 or Figure 15) and the amplitude at the point where there is no G (or G2) thereafter (be in Figure 14 or Figure 15). Then calculate using the following formula:
3.4.3 Differential gain distortion
Definition: A constant small amplitude chrominance subcarrier is superimposed on luminance signals of different levels and added to the input of the channel under test. When the luminance signal changes from the blanking level to the white level, and the average image level remains at a certain value, the change in the subcarrier amplitude at the output is called differential gain distortion.
Test method:
Add the step wave superimposed subcarrier signal D2 in Figure 6 to the input of the channel under test, and obtain the amplitude modulated subcarrier waveform after passing through a 4.43MHz bandpass filter at the output, or obtain the waveform of the amplitude modulated envelope after passing through a detector. The differential gain distortion is represented by +X% and -Y%, and its calculation formula is:
The peak-to-peak value of the differential gain distortion is obtained by the following formula: X+Y:
Where:
GB3659-83
×100%
1×100%
Amx=Amm×100%
Ae-Subcarrier amplitude or detection level at the blanking level at the output end Amx and Amn-are the maximum and minimum values of the subcarrier amplitude or detection level at each step of the output step wave (including the blanking level).
3.4.4 Differential Phase Distortion
Definition: A constant small-amplitude chrominance subcarrier without phase modulation is superimposed on the luminance signal and added to the input of the channel under test. When the luminance signal changes from the blanking level to the white level and the average image level remains at a certain specific value, the phase change of the subcarrier at the output end is called differential phase distortion.
Test method:
Add the signal in Figure 6D to the input end of the channel under test, and measure the phase of the subcarrier at each level of the step wave at the output end (including the blanking level). The phase of the subcarrier at the blanking level is used as the reference. The differential phase distortion is represented by +X and -Y, and its calculation formula is: omex
The peak-to-peak value of the differential phase distortion is obtained by the following formula X+
Each quantity in the above formulas is in degree, where:
The phase of the subcarrier at the blanking level at the output end; d
dmx and mn--are the maximum and minimum values of the subcarrier phase at each level of the step wave at the output end (including the blanking level), respectively. 3.4.5 Definition of nonlinear distortion of chrominance signal gain: The luminance signal amplitude and average image level at the input of the measured channel are fixed values, and the chrominance subcarrier amplitude changes from the specified minimum value to the specified maximum value. The deviation between the proportionality of the subcarrier at the output of the channel and the corresponding amplitude at the input is called nonlinear distortion of chrominance signal gain. Test method:
Use the three-level chrominance signal G2 in Figure 10 for measurement. The calculation formula is: D
A, -K,A2
Where: A——peak-to-peak value of the subcarrier amplitude at the output end, K,=2,1
——the position number i of the pulse string on the test signal G2 is 1 and 3 respectively (the minimum subcarrier amplitude is 1, and the maximum is i=3).
When performing the above test, the chrominance-luminance gain difference of the channel should be within the specified index range. If necessary, a subcarrier filter can be inserted between the object under test and the test instrument to eliminate the influence of harmonics. 3.4.6 Static nonlinear distortion of synchronization signal Definition: The video signal at the input end of the channel under test has a specified average image level and a synchronization signal with a nominal amplitude of 300mV. The deviation of the output synchronization pulse midpoint amplitude from the nominal value is called the static nonlinear distortion of the synchronization signal. Test method:
Add the B: signal in Figure 3 to the input end of the channel under test, use an oscilloscope to measure the synchronization pulse midpoint amplitude and nominal value at the output end (that is, the amplitude of the midpoint of 3/7 pulses is shown in Figure 16), and calculate it using the following formula: 11
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.