GB/T 11318.3-1996 Cable distribution system equipment and components for television and sound signals Part 3: General specification for television modulators
Some standard content:
1 Scope
National Standard of the People's Republic of China
Equipment and components used in cabled distribution systems primarily intended for television and sound signals Part 3: Generic specifications for TV modulator GB/T11318.3-1996
This standard specifies the product classification, requirements, test methods, inspection rules and marking, packaging, transportation and storage of TV modulators in cabled distribution systems for 5MHz~1750MHz television and sound signals. This standard applies to TV modulators in cabled distribution systems for 5MHz~1750MHz television and sound signals. 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T6510-1996 Cable distribution systems for television and sound signals GB/T11318.1-1996 Cable distribution systems for television and sound signals Equipment and components Part 1: General specifications 3 Requirements
3.1 General requirements
The general requirements for television modulators shall comply with the provisions of 4.1.1 of GB/T11318.1-1996. 3.2 Performance parameter requirements
The performance parameter requirements for television modulators are shown in Table 1. Table 1
V (peak-to-peak value)
Class approved by the State Administration of Technical Supervision on September 9, 1996
Performance parameters
1 (full TV signal)
Positive polarity (white level is positive)
Measurement method
Implementation on May 1, 1997
Accuracy
Total deviation
Video signal modulation
Flatness within the video band
Differential gain
Differential phase
Chroma/luminance delay difference
Video signal-to-noise ratio
K coefficient
Image output level
Image-to-audio power ratio
RF output impedance
Output reflection
Reflection loss
Parasitic output suppression
Sideband suppression
Image-to-audio carrier frequency spacing
Maximum frequency deviation
Pre-emphasis
In-band flatness
Distortion
Audio signal-to-noise ratio
GB/T 11318.3—1996
Table 1 (end)
Performance parameters
6002 unbalanced
or ≥10k2
unbalanced
≥105
10~20 continuously adjustable
20(—1.25 and
+6.75 MHz)
一45 (adjacent carrier frequency)
6500±5
(40 Hz--10 kHz)
≥10kn
unbalanced
75±10
6500±20
(300 Hz~7 kHz)
Measurement method
GB/T 6510 | | tt | | Chapter 12 | | tt | 1
中4.2.2.2.7
GB/T 11318. 1
4.2.2.2.7
3.3 Environmental adaptability
GB/T11318.3—1996
The environmental adaptability requirements of the TV modulator shall comply with the provisions of 4.3 of GB/T11318.1. The intermediate test item is the output level, and the qualified criterion is: the output level is within +5dB of the initial test value. The test item after the high temperature constant humidity test, sweep frequency vibration, and collision test is the modulation degree. After the climate test and mechanical test, the performance test is carried out according to the items specified in Table 1, and the test results shall comply with the relevant provisions of Table 1. 3.4 Reliability
The lower limit value of the reliability index mean time between failures (MTBF) of the TV modulator shall not be less than 5000h (Class I) and 10 000h (Class I).
The failure criterion is that the output level varies more than +5dB compared with the initial data, or the accompanying sound is abnormal. 3.5 Safety
The safety requirements of TV modulators shall comply with the relevant provisions of 4.5 of GB/T11318.1-1996. 3.6 Electromagnetic compatibility
The electromagnetic compatibility requirements of TV modulators shall comply with the provisions of 4.6 of GB/T11318.1-1996. 4 Test methods
4.1 General requirements
The test methods for general requirements of TV modulators shall be carried out in accordance with the provisions of 4.1.2 of GB/T11318.1-1996. 4.2 Performance parameters
Unless otherwise specified, all measurements are carried out under 1V (peak-to-peak) full TV signal and rated modulation. 4.2.1 Video signal modulation
4.2.1.1 Measurement block diagram
As shown in Figure 1.
Modulator under test
Video signal generator
4.2.1.2 Measurement
Standard TV demodulator
Oscilloscope
Figure 1 Equipment for measuring the modulation index of video signal Connect the video signal generator to output the step wave signal. After passing through the modulator under test and the standard TV demodulator, the step wave signal is displayed again on the oscilloscope display screen. The modulation index value can be directly read by comparing it with the standard demodulator at zero carrier pulse. Adjust the modulation index knob of the modulator under test so that the modulation index can meet the modulation index parameter requirements shown in Table 1. 4.2.2 Flatness within the video band
4.2.2.1 Measurement block diagram
As shown in Figure 2.
Video signal generator
4.2.2.2 Measurement
Modulator under test
GB/T 11318.3-1996
Standard TV demodulator
Figure 2 Equipment connection for video in-band flatness measurement OA
Oscilloscope
The video signal generator outputs a multi-burst test signal with an amplitude of 420mV (peak-to-peak). The in-band flatness within 5MHz is measured on the oscilloscope.
4.2.3 Video signal-to-noise ratio
4.2.3.1 Measurement block diagram
As shown in Figure 3.
Video signal generator
G, (1000Hz)
Audio signal generator
4.2.3.2 Measurement
Standard TV demodulator
Figure 3 Equipment connection for video signal-to-noise ratio measurement
The video signal generator outputs a 50% flat field signal (or a video signal as specified by the video noise meter). The audio signal generator outputs a 1kHz, 0.775V audio signal. Video noise meter
The high-pass filter of the video noise meter is set to 10kHz, the video low-pass filter is 5MHz, and a 4.43MHz notch is added. The video signal-to-noise ratio is directly read out using the video noise meter. 4.2.4 Image output level, image-to-sound power ratio 4.2.4.1 Measurement block diagram
As shown in Figure 4.
Video signal generator
Modulator under test
Frequency-selective voltmeter
Figure 4 Connection of equipment for measuring image output level and image-to-sound power ratio 4.2.4.2 Measurement
The modulator under test inputs a full black video signal, and uses a frequency-selective voltmeter to measure its output level at the image carrier and the sound carrier respectively. The difference between the two is the image-to-sound power ratio. 4.2.5 Output end reflection loss
4.2.5.1 Measurement block diagrambZxz.net
As shown in Figure 5.
4.2.5.2 Measurement
Sweep frequency signal generator
GB/T11318.3—1996
Spectrum analyzer
Modulator under test
Figure 5 Connection of equipment for measuring output end reflection loss 4.2.5.2.1 First, disconnect the modulator under test. The input end of the directional coupler is in a state of total reflection. At this time, a level of P is measured on the spectrum analyzer. When reading, do not read the carrier point, but take the reading of the flat part. 4.2.5.2.2 Then connect the modulator under test. A level of Q is measured on the spectrum analyzer. The reflection loss at the output end of the modulator is: V-PQ
During the measurement, the modulator needs to be powered on, but no modulation signal is added. The connection between the modulator under test and the directional coupler should be as short as possible. 4.2.6 Parasitic output suppression
4.2.6.1 The measurement block diagram
is shown in Figure 6.
Tested modulator
Spectrum analyzer
Figure 6 Equipment connection for parasitic output suppression measurement 4.2.6.2 Measurement
The output level of the tested modulator is the nominal output level specified for the product; within the operating frequency band of the product, the image carrier level and the maximum parasitic output signal level are measured on the spectrum analyzer, and the level difference between the two is the parasitic output suppression. 4.2.7 K factor
4.2.7.1 Measurement block diagram
As shown in Figure 7.
Video signal generator
4.2.7.2 Measurement
Tested modulator
Standard TV demodulator
Figure 7 Equipment connection for K factor measurement
Video analyzer
The K factor refers to the change in the waveform of the 2T sine square pulse and bar pulse caused by the front-end equipment. The K factor is the standard rated value of transient waveform distortion that is included in the subjective quality evaluation. The K factor includes three coefficients: the K factor of 2T sine square pulse (K,), the K factor of 2T pulse and bar pulse (Kp) and the K factor of bar signal flat top (K). The largest one among the three coefficients is taken as the K factor value. Here, T=83ns is taken. The output pulse and bar test signal of the test signal generator are shown in Figure 8: 345
—300
GB/T11318.3-1996
64μus
Figure 827° sine square pulse and bar pulse
Use the K factor scale plate of the waveform monitor to read K, Kpb, Kb, and take the maximum value of the three as the K factor. 4.2.8 Sideband suppression
4.2.8.1 Measurement block diagram
As shown in Figure 9.
G(0～10MHz)
Video signal generator
4.2.8.2 Measurement
TV test signal generator
Oscilloscope
Modulator under test
Figure 9 Equipment connection for sideband suppression measurement
The test signal is a flat field plus a sine wave, as shown in Figure 10: S=0.2V
Brightness level is U-0.35V
The superimposed sine wave is a swept frequency signal of 0～10MHz.S=0.2V Figure 10) Sideband suppression test signal
Spectrum analyzer or frequency selection table
The modulation degree of the modulator under test is calibrated at the nominal modulation degree when the video signal is input with 1V (peak-to-peak value). Use the relevant attenuator on the spectrum analyzer to read the decibel change of each frequency point relative to the response at f, +1.5MHz. That is: take f, +1.5MHz as reference (0dB), read out the decibel number of the response reduction at other frequency points, f represents the image carrier frequency. The sideband suppression needs to achieve:
The response attenuation at the channel edge, i.e. f-1.25MHz and f, +6.75MHz, is ≥20dB, and the response attenuation at the adjacent image and sound carrier frequencies and other channels is ≥45dB. 4.2.9 Maximum frequency deviation of the accompanying audio signal
4.2.9.1 The measurement block diagram
is shown in Figure 11.
4.2.9.2 Measurement
Audio signal generator
GB/T11318.3—1996
Tested modulator
Standard TV demodulator
Equipment connection for maximum frequency deviation measurement
The audio signal generator outputs a 1kHz, 0.775V signal. The frequency deviation value read out on the standard TV demodulator is the maximum frequency deviation. 4.2.10 Flatness in the sound band
4.2.10.1 The measurement block diagram
is shown in Figure 12.
Audio signal generator
4.2.10.2 Measurement
Measured modulator
Standard TV demodulator
Figure 12 The equipment for measuring the flatness in the sound band is connected within the frequency range specified in Table 1. The audio signal generator outputs a 0.19V audio frequency signal. Audio millivoltmeter
Use a 50us standard TV to demodulate the audio signal, and measure the difference between the level of each frequency point and the level of the 1kHz point on the audio level meter. The maximum value is the flatness in the sound band. 4.2.11 Sound distortion
4.2.11.1 The measurement block diagram
is shown in Figure 13.
Measured modulator
Audio signal generator
Standard TV demodulator
Figure 13 Equipment connection for audio distortion measurement 4.2.11.2 Measurement
The standard audio signal generator outputs a 1kHz sine wave. Distortion meter
Adjust the output amplitude of the audio signal generator so that the frequency deviation reading on the standard TV demodulator is ±60kHz. At this time, use the distortion meter to read the distortion value.
4.2.12 Audio signal-to-noise ratio
4.2.12.1 Measurement block diagram
As shown in Figure 14.
Video signal generator
Audio signal generator
4.2.12.2 Measurement
The video signal is a black field TV signal.
GB/T 11318. 3--1996
Standard TV demodulator
Figure 14 Equipment for audio signal-to-noise ratio measurement Connect the audio voltmeter
The audio signal generator outputs a 1kHz, 0.775V signal. At this time, the modulator under test should be calibrated at a frequency deviation of 50kHz, and the image-sound power ratio is 10dB.
Read the amplitude of the 1kHz signal on the audio millivoltmeter, then turn off the audio signal generator and read the noise amplitude on the audio millivoltmeter. The ratio of the two is the audio signal-to-noise ratio, expressed in decibels. A 10kHz low-pass filter is added before the audio millivoltmeter. 4.3 Environmental adaptation
The environmental adaptability test method of the TV modulator shall be carried out in accordance with the provisions of 4.3 of GB/T11318.1-1996. The test temperature group is Group I.
4.4 Reliability
The reliability test method of the TV modulator shall be carried out in accordance with the provisions of 4.4 of GB/T11318.1-1996. The test plan is Plan II. 4.5 Safety
The safety test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.5 of GB/T11318.1-1996. 4.6 Electromagnetic compatibility
The electromagnetic compatibility test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.6 of GB/T11318.1-1996. 5 Inspection rules
The inspection rules of the TV modulator shall comply with the provisions of Chapter 5 of GB/T11318.1-1996. The main electrical performance parameter detection items during the acceptance inspection are modulation, frequency accuracy, image output level and image and sound carrier frequency spacing. 6 Marking, packaging, transportation and storage
The marking, packaging, transportation and storage of TV modulators shall comply with the relevant provisions of Chapter 6 of GB/T11318.1-1996. 3482 Measurement
Tested modulator
Standard TV demodulator
Figure? K-factor measurement equipment connection
Video analyzer
K-factor refers to the change in the waveform of 2T sine square pulse and bar pulse caused by the front-end equipment. K-factor is the standard rated value of transient waveform distortion included in subjective quality evaluation. K-factor includes three coefficients: K-factor of 2T sine square pulse (K,), K-factor of 2T pulse and bar pulse (Kp) and K-factor of flat top of bar signal (K). The largest one among the three coefficients is taken as K-factor value. Here, T=83ns is taken. The test signal generator outputs pulse and bar test signals as shown in Figure 8: 345
—300
GB/T11318.3-1996
64μus
Figure 827° sine square pulse and bar pulse
Use the K factor scale plate of the waveform monitor to read K, Kpb, Kb, and take the maximum value of the three as the K factor. 4.2.8 Sideband suppression
4.2.8.1 Measurement block diagram
As shown in Figure 9.
G(0～10MHz)
Video signal generator
4.2.8.2 Measurement
TV test signal generator
Oscilloscope
Modulator under test
Figure 9 Equipment connection for sideband suppression measurement
The test signal is a flat field plus a sine wave, as shown in Figure 10: S=0.2V
Brightness level is U-0.35V
The superimposed sine wave is a swept frequency signal of 0～10MHz.S=0.2V Figure 10) Sideband suppression test signal
Spectrum analyzer or frequency selection table
The modulation degree of the modulator under test is calibrated at the nominal modulation degree when the video signal is input with 1V (peak-to-peak value). Use the relevant attenuator on the spectrum analyzer to read the decibel change of each frequency point relative to the response at f, +1.5MHz. That is: take f, +1.5MHz as reference (0dB), read out the decibel number of the response reduction at other frequency points, f represents the image carrier frequency. The sideband suppression needs to achieve:
The response attenuation at the channel edge, i.e. f-1.25MHz and f, +6.75MHz, is ≥20dB, and the response attenuation at the adjacent image and sound carrier frequencies and other channels is ≥45dB. 4.2.9 Maximum frequency deviation of the accompanying audio signal
4.2.9.1 The measurement block diagram
is shown in Figure 11.
4.2.9.2 Measurement
Audio signal generator
GB/T11318.3—1996
Tested modulator
Standard TV demodulator
Equipment connection for maximum frequency deviation measurement
The audio signal generator outputs a 1kHz, 0.775V signal. The frequency deviation value read out on the standard TV demodulator is the maximum frequency deviation. 4.2.10 Flatness in the sound band
4.2.10.1 The measurement block diagram
is shown in Figure 12.
Audio signal generator
4.2.10.2 Measurement
Measured modulator
Standard TV demodulator
Figure 12 The equipment for measuring the flatness in the sound band is connected within the frequency range specified in Table 1. The audio signal generator outputs a 0.19V audio frequency signal. Audio millivoltmeter
Use a 50us standard TV to demodulate the audio signal, and measure the difference between the level of each frequency point and the level of the 1kHz point on the audio level meter. The maximum value is the flatness in the sound band. 4.2.11 Sound distortion
4.2.11.1 The measurement block diagram
is shown in Figure 13.
Measured modulator
Audio signal generator
Standard TV demodulator
Figure 13 Equipment connection for audio distortion measurement 4.2.11.2 Measurement
The standard audio signal generator outputs a 1kHz sine wave. Distortion meter
Adjust the output amplitude of the audio signal generator so that the frequency deviation reading on the standard TV demodulator is ±60kHz. At this time, use the distortion meter to read the distortion value.
4.2.12 Audio signal-to-noise ratio
4.2.12.1 Measurement block diagram
As shown in Figure 14.
Video signal generator
Audio signal generator
4.2.12.2 Measurement
The video signal is a black field TV signal.
GB/T 11318. 3--1996
Standard TV demodulator
Figure 14 Equipment for audio signal-to-noise ratio measurement Connect the audio voltmeter
The audio signal generator outputs a 1kHz, 0.775V signal. At this time, the modulator under test should be calibrated at a frequency deviation of 50kHz, and the image-sound power ratio is 10dB.
Read the amplitude of the 1kHz signal on the audio millivoltmeter, then turn off the audio signal generator and read the noise amplitude on the audio millivoltmeter. The ratio of the two is the audio signal-to-noise ratio, expressed in decibels. A 10kHz low-pass filter is added before the audio millivoltmeter. 4.3 Environmental adaptation
The environmental adaptability test method of the TV modulator shall be carried out in accordance with the provisions of 4.3 of GB/T11318.1-1996. The test temperature group is Group I.
4.4 Reliability
The reliability test method of the TV modulator shall be carried out in accordance with the provisions of 4.4 of GB/T11318.1-1996. The test plan is Plan II. 4.5 Safety
The safety test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.5 of GB/T11318.1-1996. 4.6 Electromagnetic compatibility
The electromagnetic compatibility test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.6 of GB/T11318.1-1996. 5 Inspection rules
The inspection rules of the TV modulator shall comply with the provisions of Chapter 5 of GB/T11318.1-1996. The main electrical performance parameter detection items during the acceptance inspection are modulation, frequency accuracy, image output level and image and sound carrier frequency spacing. 6 Marking, packaging, transportation and storage
The marking, packaging, transportation and storage of TV modulators shall comply with the relevant provisions of Chapter 6 of GB/T11318.1-1996. 3482 Measurement
Tested modulator
Standard TV demodulator
Figure? K-factor measurement equipment connection
Video analyzer
K-factor refers to the change in the waveform of 2T sine square pulse and bar pulse caused by the front-end equipment. K-factor is the standard rated value of transient waveform distortion included in subjective quality evaluation. K-factor includes three coefficients: K-factor of 2T sine square pulse (K,), K-factor of 2T pulse and bar pulse (Kp) and K-factor of flat top of bar signal (K). The largest one among the three coefficients is taken as K-factor value. Here, T=83ns is taken. The test signal generator outputs pulse and bar test signals as shown in Figure 8: 345
—300
GB/T11318.3-1996
64μus
Figure 827° sine square pulse and bar pulse
Use the K factor scale plate of the waveform monitor to read K, Kpb, Kb, and take the maximum value of the three as the K factor. 4.2.8 Sideband suppression
4.2.8.1 Measurement block diagram
As shown in Figure 9.
G(0～10MHz)
Video signal generator
4.2.8.2 Measurement
TV test signal generator
Oscilloscope
Modulator under test
Figure 9 Equipment connection for sideband suppression measurement
The test signal is a flat field plus a sine wave, as shown in Figure 10: S=0.2V
Brightness level is U-0.35V
The superimposed sine wave is a swept frequency signal of 0～10MHz.S=0.2V Figure 10) Sideband suppression test signal
Spectrum analyzer or frequency selection table
The modulation degree of the modulator under test is calibrated at the nominal modulation degree when the video signal is input with 1V (peak-to-peak value). Use the relevant attenuator on the spectrum analyzer to read the decibel change of each frequency point relative to the response at f, +1.5MHz. That is: take f, +1.5MHz as reference (0dB), read out the decibel number of the response reduction at other frequency points, f represents the image carrier frequency. The sideband suppression needs to achieve:
The response attenuation at the channel edge, i.e. f-1.25MHz and f, +6.75MHz, is ≥20dB, and the response attenuation at the adjacent image and sound carrier frequencies and other channels is ≥45dB. 4.2.9 Maximum frequency deviation of the accompanying audio signal
4.2.9.1 The measurement block diagram
is shown in Figure 11.
4.2.9.2 Measurement
Audio signal generator
GB/T11318.3—1996
Tested modulator
Standard TV demodulator
Equipment connection for maximum frequency deviation measurement
The audio signal generator outputs a 1kHz, 0.775V signal. The frequency deviation value read out on the standard TV demodulator is the maximum frequency deviation. 4.2.10 Flatness in the sound band
4.2.10.1 The measurement block diagram
is shown in Figure 12.
Audio signal generator
4.2.10.2 Measurement
Measured modulator
Standard TV demodulator
Figure 12 The equipment for measuring the flatness in the sound band is connected within the frequency range specified in Table 1. The audio signal generator outputs a 0.19V audio frequency signal. Audio millivoltmeter
Use a 50us standard TV to demodulate the audio signal, and measure the difference between the level of each frequency point and the level of the 1kHz point on the audio level meter. The maximum value is the flatness in the sound band. 4.2.11 Sound distortion
4.2.11.1 The measurement block diagram
is shown in Figure 13.
Measured modulator
Audio signal generator
Standard TV demodulator
Figure 13 Equipment connection for audio distortion measurement 4.2.11.2 Measurement
The standard audio signal generator outputs a 1kHz sine wave. Distortion meter
Adjust the output amplitude of the audio signal generator so that the frequency deviation reading on the standard TV demodulator is ±60kHz. At this time, use the distortion meter to read the distortion value.
4.2.12 Audio signal-to-noise ratio
4.2.12.1 Measurement block diagram
As shown in Figure 14.
Video signal generator
Audio signal generator
4.2.12.2 Measurement
The video signal is a black field TV signal.
GB/T 11318. 3--1996
Standard TV demodulator
Figure 14 Equipment for audio signal-to-noise ratio measurement Connect the audio voltmeter
The audio signal generator outputs a 1kHz, 0.775V signal. At this time, the modulator under test should be calibrated at a frequency deviation of 50kHz, and the image-sound power ratio is 10dB.
Read the amplitude of the 1kHz signal on the audio millivoltmeter, then turn off the audio signal generator and read the noise amplitude on the audio millivoltmeter. The ratio of the two is the audio signal-to-noise ratio, expressed in decibels. A 10kHz low-pass filter is added before the audio millivoltmeter. 4.3 Environmental adaptation
The environmental adaptability test method of the TV modulator shall be carried out in accordance with the provisions of 4.3 of GB/T11318.1-1996. The test temperature group is Group I.
4.4 Reliability
The reliability test method of the TV modulator shall be carried out in accordance with the provisions of 4.4 of GB/T11318.1-1996. The test plan is Plan II. 4.5 Safety
The safety test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.5 of GB/T11318.1-1996. 4.6 Electromagnetic compatibility
The electromagnetic compatibility test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.6 of GB/T11318.1-1996. 5 Inspection rules
The inspection rules of the TV modulator shall comply with the provisions of Chapter 5 of GB/T11318.1-1996. The main electrical performance parameter detection items during the acceptance inspection are modulation, frequency accuracy, image output level and image and sound carrier frequency spacing. 6 Marking, packaging, transportation and storage
The marking, packaging, transportation and storage of TV modulators shall comply with the relevant provisions of Chapter 6 of GB/T11318.1-1996. 3481 Measurement block diagram
As shown in Figure 12.
Audio signal generator
4.2.10.2 Measurement
Measured modulator
Standard TV demodulator
Figure 12 The equipment for measuring the flatness in the sound band is connected within the frequency range specified in Table 1. The audio signal generator outputs a 0.19V audio frequency signal. Audio millivoltmeter
Use a 50us standard TV to demodulate the audio signal, and measure the difference between the level of each frequency point and the level of the 1kHz point on the audio level meter. The maximum value is the flatness in the sound band. 4.2.11 Sound distortion
4.2.11.1 Measurement block diagram
As shown in Figure 13.
Measured modulator
Audio signal generator
Standard TV demodulator
Figure 13 Equipment connection for audio distortion measurement 4.2.11.2 Measurement
The standard audio signal generator outputs a 1kHz sine wave. Distortion meter
Adjust the output amplitude of the audio signal generator so that the frequency deviation reading on the standard TV demodulator is ±60kHz. At this time, use the distortion meter to read the distortion value.
4.2.12 Audio signal-to-noise ratio
4.2.12.1 Measurement block diagram
As shown in Figure 14.
Video signal generator
Audio signal generator
4.2.12.2 Measurement
The video signal is a black field TV signal.
GB/T 11318. 3--1996
Standard TV demodulator
Figure 14 Equipment for audio signal-to-noise ratio measurement Connect the audio voltmeter
The audio signal generator outputs a 1kHz, 0.775V signal. At this time, the modulator under test should be calibrated at a frequency deviation of 50kHz, and the image-sound power ratio is 10dB.
Read the amplitude of the 1kHz signal on the audio millivoltmeter, then turn off the audio signal generator and read the noise amplitude on the audio millivoltmeter. The ratio of the two is the audio signal-to-noise ratio, expressed in decibels. A 10kHz low-pass filter is added before the audio millivoltmeter. 4.3 Environmental adaptation
The environmental adaptability test method of the TV modulator shall be carried out in accordance with the provisions of 4.3 of GB/T11318.1-1996. The test temperature group is Group I.
4.4 Reliability
The reliability test method of the TV modulator shall be carried out in accordance with the provisions of 4.4 of GB/T11318.1-1996. The test plan is Plan II. 4.5 Safety
The safety test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.5 of GB/T11318.1-1996. 4.6 Electromagnetic compatibility
The electromagnetic compatibility test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.6 of GB/T11318.1-1996. 5 Inspection rules
The inspection rules of the TV modulator shall comply with the provisions of Chapter 5 of GB/T11318.1-1996. The main electrical performance parameter detection items during the acceptance inspection are modulation, frequency accuracy, image output level and image and sound carrier frequency spacing. 6 Marking, packaging, transportation and storage
The marking, packaging, transportation and storage of TV modulators shall comply with the relevant provisions of Chapter 6 of GB/T11318.1-1996. 3481 Measurement block diagram
As shown in Figure 12.
Audio signal generator
4.2.10.2 Measurement
Measured modulator
Standard TV demodulator
Figure 12 The equipment for measuring the flatness in the sound band is connected within the frequency range specified in Table 1. The audio signal generator outputs a 0.19V audio frequency signal. Audio millivoltmeter
Use a 50us standard TV to demodulate the audio signal, and measure the difference between the level of each frequency point and the level of the 1kHz point on the audio level meter. The maximum value is the flatness in the sound band. 4.2.11 Sound distortion
4.2.11.1 Measurement block diagram
As shown in Figure 13.
Measured modulator
Audio signal generator
Standard TV demodulator
Figure 13 Equipment connection for audio distortion measurement 4.2.11.2 Measurement
The standard audio signal generator outputs a 1kHz sine wave. Distortion meter
Adjust the output amplitude of the audio signal generator so that the frequency deviation reading on the standard TV demodulator is ±60kHz. At this time, use the distortion meter to read the distortion value.
4.2.12 Audio signal-to-noise ratio
4.2.12.1 Measurement block diagram
As shown in Figure 14.
Video signal generator
Audio signal generator
4.2.12.2 Measurement
The video signal is a black field TV signal.
GB/T 11318. 3--1996
Standard TV demodulator
Figure 14 Equipment for audio signal-to-noise ratio measurement Connect the audio voltmeter
The audio signal generator outputs a 1kHz, 0.775V signal. At this time, the modulator under test should be calibrated at a frequency deviation of 50kHz, and the image-sound power ratio is 10dB.
Read the amplitude of the 1kHz signal on the audio millivoltmeter, then turn off the audio signal generator and read the noise amplitude on the audio millivoltmeter. The ratio of the two is the audio signal-to-noise ratio, expressed in decibels. A 10kHz low-pass filter is added before the audio millivoltmeter. 4.3 Environmental adaptation
The environmental adaptability test method of the TV modulator shall be carried out in accordance with the provisions of 4.3 of GB/T11318.1-1996. The test temperature group is Group I.
4.4 Reliability
The reliability test method of the TV modulator shall be carried out in accordance with the provisions of 4.4 of GB/T11318.1-1996. The test plan is Plan II. 4.5 Safety
The safety test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.5 of GB/T11318.1-1996. 4.6 Electromagnetic compatibility
The electromagnetic compatibility test method of the TV modulator shall be carried out in accordance with the relevant provisions of 4.6 of GB/T11318.1-1996. 5 Inspection rules
The inspection rules of the TV modulator shall comply with the provisions of Chapter 5 of GB/T11318.1-1996. The main electrical performance parameter detection items during the acceptance inspection are modulation, frequency accuracy, image output level and image and sound carrier frequency spacing. 6 Marking, packaging, transportation and storage
The marking, packaging, transportation and storage of TV modulators shall comply with the relevant provisions of Chapter 6 of GB/T11318.1-1996. 348
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