This standard specifies the test method for the distortion of the chrominance signal caused by the different brightness signal levels of the transmitting tube. This standard applies to the transmitting tube used in television transmitting equipment. GB/T 3789.30-1991 Transmitter electrical performance test method Test method for the distortion of the chrominance signal (differential gain DG and differential phase PP) caused by different brightness signals GB/T3789.30-1991 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Test methods for electrical properties of trausmitting tubes
Test methods for the distortion of chrominance signal due to the luminance (differential gain DG and differential phase DP)
Measurements of the electrical properties of trausmitting tubesMethods of measuring the distortion in the chrominance signal due to the luminance (dirferentlal gain and dfferential phase)Subject content and scope of application
GB/T 3789-30—91
This standard specifies the test methods for the distortion of chrominance signal caused by different luminance signal levels in trausmitting tubes. This standard applies to trausmitting tubes used in television transmission equipment. 2 Reference standards
GB/T3789.1 General rules for testing the electrical properties of transmitting tubes GB6277 Measurement methods for television transmitters
3 Terms
Distortion in the chrominance signal due to the luminance level
Add a constant small-amplitude chrominance subcarrier to different luminance levels and add it to the input end of the amplifier driver of the tube under test. When the luminance level changes from the blanking level to the white level, and the average picture level remains at a certain value, the amplitude of the superimposed subcarrier demodulated by the amplifier output and its phase change relative to the chrominance subcarrier signal on the blanking level are called chrominance signal distortion caused by different luminance levels. The change in amplitude is called differential gain (DG), and the change in phase is called differential phase (DP). The differential gain is generally expressed in percentage:
Wu Zhong: DG
Positive differential gain 1
Negative differential gain:
= A × 100%
As - Al × 100%
The peak-to-peak amplitude of the chrominance subcarrier at the output end is equivalent to the blanking level, 1)
The maximum value of the subcarrier peak-to-peak amplitude in the output-line period (in the formula, it specifically refers to the maximum value of the subcarrier peak-to-peak amplitude with an amplitude greater than A.);
Approved by the State Administration of Technical Supervision on August 15, 1991 and implemented on April 1, 1992
GB/T 3789. 30-91
The minimum value of the subcarrier peak-to-peak amplitude in a line period at the output end (in the formula, it specifically refers to the minimum value of the subcarrier peak-to-peak amplitude with an amplitude less than A).
When the actual amplitude of the distorted waveform is greater than A, DG is positive, and when it is less than A, DG is negative. The total differential gain DG is:
Aax _ Amm × 100%
-DG- DG
h. The differential phase is often based on the phase of the chrominance subcarrier at the blanking level. When the chrominance subcarrier phase at other brightness levels leads the phase of the reference level, DP is positive, otherwise it is negative: DP+=+(-)
DP_= -( )
Where: P+
Positive differential phase;
Negative differential phase;
——The chrominance subcarrier phase at the blanking level, degree,-the chrominance subcarrier phase before the other brightness level step, degree p
The chrominance subcarrier phase after the other brightness level step, degree. The total differential phase DP is:
DP = DP+- DP_ = —
4 Test block diagram
The test block diagram is shown in Figure 1.
Test signal generation demodulator
waveform A
Monitor end B
Digital oscilloscope
or DG.DP measuring instrument
Exciter
Spot measuring tube
Amplifier end
[Image demodulator
Figure 1 Differential gain, differential phase test block diagram Test load
b. When the waveform monitor does not have a 4. 43 MHz band-pass filter, a 4. 43 MHz band-pass filter should be added between the demodulator and the waveform monitor.
5 Test equipment and test rules
Test equipment and test rules shall comply with the provisions of GB/T3789.1 and Chapter 4 of GB6277. 6 Test method
6.1 Apply voltage to each pole according to the specification.
GB/T 3789. 3091
6.2 Test signal The generator sends the test signal D (APL=12.5%, 50%87.5%) as shown in Figure 2. The frequency of the superimposed sine signal is 4.43 MHz and the amplitude is 140 mV. 6.3 Use a loss oscilloscope or DG, DP tester to measure the DG and DP values ​​when APL=12.5%, 50%, and 87.5% respectively. m
a. APL.=50% Peak-to-peak amplitude of superimposed chrominance signal 140mVmv
b- APL=12.5%
C. APL= 87.5%
Figure 2 Test signal D (staircase wave superimposed subcarrier) 7bzxZ.net
Data processing
GB/T 3789. 30-91
Select the largest data in 6.3 as the DG and DP of the tube under test, and indicate the corresponding average picture level at the same time. b. When not using the total DG and DP, the positive or negative value of DG and DP should be indicated. Additional remarks:
This standard was proposed by the Ministry of Machinery and Electronics Industry of the People's Republic of China. This standard was drafted by the Electronic Standardization Institute of the Ministry of Machinery and Electronics Industry and Factory 779.
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