This standard specifies the test method for three-tone intermodulation distortion of transmitting tubes. This standard applies to transmitting tubes used in television transmitting equipment. GB/T 3789.27-1991 Test method for electrical performance of transmitting tubes Test method for three-tone intermodulation distortion GB/T3789.27-1991 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Test methods for electrical properties of transmitting tubes
Test methods for three-tone intermodulation distortion
Measurements of the electrical properties of transmitting tubesMethods of measuring the inter-modulation distortion of a three tone signal
1 Subject content and scope of application
This standard specifies the test methods for three-tone intermodulation distortion of transmitting tubes. This standard applies to transmitting tubes used in electrical transmitter equipment. 2 Reference standards
GB/T3789.1 General principles for testing the electrical properties of transmitting tubes GB6277 Measurement methods for television transmitters
3 Terms
Intermodulation distortion of a threetonc signalGB/T 3789.27-91
Three-tone (three-frequency) five-tone distortion refers to the ratio of the maximum intermodulation power level on a pure resistance load within the specified frequency band of the transmitting tube amplifier to the specified reference level (synchronous top level) when the transmitting tube is under the specified working state and the specified three frequencies, frequency intervals and power level signals are used as test signals. It is expressed in minutes.
Test block diagram
The test block diagram is shown in Figure 1.
Three-tone signal booster
State Technical Supervision Bureau approved the test
Amplifier
CouplerWww.bzxZ.net
Frequency Discussion
Three-tone intermodulation distortion test block diagram
Through type
1992-04-01 implementation
GB/T 3789. 2791
Among them, the signal excitation device can be composed of two ways. Mode A, using audio signal exciter
Mode B uses video input to send test signal K. (a=350mV, 8=700mV) as shown in Figure 2, superimposing the color subcarrier signal with an oscillation frequency of 4.43MHz.
5 Test equipment and test rules
64 μs
Figure 2 Test signal K (flat field plus sine wave) Test equipment and test rules shall comply with the provisions of GB6277.1 and Chapter 4 of GB6277. The frequency and output amplitude of the three-tone signal exciter must have a sufficiently high stability. h.
The amplitude, frequency and frequency interval of the carrier frequency three-tone signal input to the tube under test shall comply with the provisions of Figure 3. The intermodulation distortion index of the three-tone signal exciter itself shall be 10dB better than the intermodulation distortion of the tube under test. Envelope correction and high-frequency negative feedback shall not be added to improve the intermodulation distortion. Requirements for equipment
The directivity coefficient of the directional coupler shall be greater than 20B. The frequency range of the spectrum analyzer shall meet the test requirements; the amplitude measurement range is 0~70 dB; the intermodulation distortion itself shall be better than -65 dB. 6 Test method
Perform according to method A.
Digital test output level
Output power voltage
6.1.1Add voltages to each pole according to the specification.
f,+fa-fao
Intermodulation distortion
(level difference)
Figure 3 Distribution diagram of three-tone intermodulation spectrum
Frequency MHz
GB/T 3789. 27-91
6.1.2Adjust the tube amplifier under test to the specified working state. 6.1.3Add excitation signal f, so that the output of the tube amplifier under test reaches the specified power value. At this time, the indication value of the spectrum analyzer is printed as the specified output reference level (regarded as 0dB).
6. 1. 4 Adjust the amplitude of f to -8 dB. 6.1.5Add excitation signal f, and adjust the amplitude of f to -10dB. 6.1.6 Add the excitation signal fe to adjust the amplitude of f to -16 dB. 6.1.7
number).
The decibel number of the three-tone intermodulation distortion of the tested tube in the open circuit can be read on the spectrum analyzer (relative to the decibel of the reference output level). 6.2 Perform according to method B
6.2.1 Add the voltage of each pole according to the specification.
6.2.2 Adjust the amplifier of the tested tube to the specified working state. 6.2.3 The test signal generator sends the test signal K (α-0mV), and the black envelope level meets the standard, so that the output of the amplifier of the tested tube reaches the specified power value. At this time, the indication value of the spectrometer is the specified output reference voltage (regarded as B) 6.2.4 The test signal generator sends the test signal K (u=350mV), on which is superimposed a 4.43MHz equal-amplitude sine oscillation with an amplitude of 700.mV; add the accompanying sound carrier frequency.
6.2.5 Use the spectrum analyzer to select the frequency to be tested, so that fJ. The signal levels of the three tones f are -8dB, -10dB, and 16dB respectively (relative to the output reference level of 10).
6.2.6 Read the level of the intermodulation component from the spectrum analyzer (as shown in Figure 3), and measure the decibel number of the maximum intermodulation component at f in the frequency band. In order to show the true intermodulation level, the bandwidth of the instrument shall not be less than 300kHz. Note: ① The above test must be carried out when the input and auxiliary output of the tube amplifier under test are adjusted to the best matching state. ② The frequency is set to the missing carrier frequency, f is the accompanying sound carrier frequency, f is the color subcarrier frequency, and f is the intermodulation distortion factor (5, -10 + -f). ③ When reading, it is necessary to exclude the influence of random noise components. Additional remarks:
This standard is proposed by the Ministry of Machinery and Electronics Industry of the People's Republic of China. This standard is initiated by the Electronic Standardization Institute of the Ministry of Machinery and Electronics Industry and Factory 779.
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