GB/T 11298.3-1997 Measurement methods for satellite television earth receiving stations - Outdoor unit measurements
Some standard content:
GB/T11298.3--1997
This standard is a revised version of GB11298.3-89 "Satellite TV Earth Receiving Station Measurement Method Outdoor Unit Measurement". With the development of science and technology, it has become a reality to measure the technical parameters of outdoor units with advanced instruments. For this reason, some measurement methods in GB.11298.3-89 are revised. Considering that some manufacturers' measuring instruments are not advanced, but the original standard measurement methods can still measure the technical parameters of outdoor units, some reasonable and effective measurement methods are retained. This standard has made the following revisions to the original version: 1. Use precision receivers as level meters to measure the noise temperature of outdoor units. 1. Use high-sensitivity spectrum analyzers instead of precision variable attenuators, small power meters, detectors and other instruments to measure the technical parameters of outdoor units, thereby simplifying the test equipment and improving the measurement accuracy. 1. When using the swept frequency method to measure technical parameters, use instruments such as spectrum analyzers and swept frequency signal generators to simplify the measurement method. In this standard, the calculation formula for the stability of the local oscillator frequency has been modified. This standard shall replace GB11298.3--89 from the date of implementation. This standard is proposed by the Ministry of Electronics Industry of the People's Republic of China. This standard is under the jurisdiction of the Standardization Institute of the Ministry of Electronics Industry. The drafting units of this standard are the 54th Institute of the Ministry of Electronics Industry and the Broadcasting Science Research Institute of the Ministry of Radio, Film and Television. The main drafters of this standard are Wang Xiangjun and Jiang Huijuan. This standard was first issued on March 31, 1989 and revised for the first time in August 1997. 23
1 Scope
National Standard of the People's Republic of China
Methods of measurement for satellitetelevisionearth receive-only stationDoor-out unit measurement
This standard specifies the measurement methods for outdoor units of satellitetelevisionearth receive-only stations. This standard is applicable to the measurement of the electrical properties of outdoor units of satellitetelevisionearth receive-only stations. 2 Reference standards
GB/T11298.3—1997
Replaces GB11298.3—89
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/T11442—1995 General technical conditions for satellite TV earth receiving stations 3 Measurement conditions
3.1 Atmospheric conditions
Measurement temperature: 15℃～35℃ (20℃～25℃ when measuring noise temperature), measurement humidity: 45%～75%;
Atmospheric pressure: 86kPa～106kPa.
3.2 Environmental conditions
The measurement environment should meet the requirements of electromagnetic compatibility. 4 Measurement method
4.1 Working frequency band
4.1.1 General considerations
The working frequency band of the outdoor unit refers to the RF frequency range that meets the specified electrical performance indicators, which is determined by the upper and lower limits of the frequency. 4.1.2 Measurement method
Sweep frequency method: Directly use a sweep frequency meter to measure, and the measurement equipment configuration is shown in Figure 1. Approved by the State Administration of Technical Supervision on August 26, 199724
Implementation on May 1, 1998
The measurement steps are as follows:
Waveguide conversion
GB/T 11298. 3--1997
DC isolation
Electric boost circuit
Figure 1 Equipment configuration for measuring the working frequency band
Sweep frequency meter
a) Do not connect the coaxial waveguide conversion, outdoor unit and power supply first. Adjust the signal source to the specified sweep output frequency range (e.g. 3.7GHz ~ 4.2GHz) and output level (e.g. -70 dBm), a flat baseline is displayed on the screen of the sweep frequency meter, and the baseline is recorded, while increasing the gain measurement of each grid; b) Connect the coaxial waveguide conversion, outdoor unit and power supply; at this time, another line with gain should be swept out, which is about 60dB different from the baseline. This is the sweep frequency curve of the outdoor unit;
c) Observe the sweep frequency curve. Within the sweep frequency range, the peak-to-peak difference does not exceed the specified value. The sweep frequency range is the working frequency band of the outdoor unit.
4.1.3 Result Representation
Use curves or text descriptions.
4.2 Amplitude/Frequency Characteristics
4.2.1 General Considerations
Amplitude/Frequency Characteristics refers to the relationship between output level and frequency when the input level (in the linear state) remains constant. 4.2.2 Measurement method
4.2.2.1 According to 4.1.2, use the frequency sweep method to measure, and observe the gain fluctuation (peak-to-peak value) within the passband, which is the amplitude/frequency characteristic. Another frequency sweep method is to use a frequency sweep signal source and a spectrum analyzer for measurement, and the measurement equipment configuration is shown in Figure 2. 4.2.2.2
Signal source
The measurement steps are as follows:
DC isolation
Analyzer
Figure 2 Equipment configuration for measuring amplitude/frequency characteristics with a spectrum analyzer Printer
a) Set the starting frequency of the frequency sweep signal source to the lowest frequency of the working frequency band, the ending frequency to the highest frequency of the working frequency band, and keep it in the frequency sweep state. The output level should be less than or equal to -70dBm; b) Adjust the spectrum analyzer to display the output curve within the working frequency band, use the display line or MAK to indicate the peak-to-peak value of the curve, and print out the curve with a printer. 4.2.3 Result Expression
Express with a curve or explain with words.
4.3 Gain Fluctuation in Any Receive Channel in Band 4.3.1 General Consideration
Gain fluctuation in any receive channel in band refers to the power gain fluctuation in any 36MHz bandwidth in the passband of the outdoor unit. 25
4.3.2 Measurement Method
GB/T11298.3—1997
According to the measurement method specified in 4.2.2, measure the amplitude/frequency characteristics in any 36MHz band. 4.3.3 Result Expression
Express with a curve or explain with words.
4.4 Power Gain
4.4.1 General Consideration
Power gain is the ratio of the output power of the specified outdoor unit to the input power, expressed in decibels. 4.4.2 Measurement method
4.4.2.1 When the frequency sweep method is used, measure according to the method specified in 4.1.2. 4.4.2.2 Use the point frequency measurement method to measure, and the measurement equipment configuration is shown in Figure 3. Frequency
Synthesizer
Measurement steps are as follows:
Waveguide conversion
According to the DC
Figure 3 Point frequency measurement method to measure power gain Equipment configuration Spectrum analyzer
Or level meter
a) Adjust the frequency synthesizer output level, which should be the linear input level of the outdoor unit, and record this data A (dBm). Calibrate at least one frequency point every 50MHz,
b) Connect the outdoor unit to be tested, and read the level A, (dBm) of the corresponding output frequency point at the specified frequency point; c) Calculate the value of A2 (dBm)-A, (dBm) of each test point in turn, which is the power gain of the outdoor unit. 4.4.3 Result Expression
Use curve or text description.
4.5 Noise Temperature
4.5.1 General Consideration
Noise temperature refers to the equivalent noise temperature T of the outdoor unit input port. The unit is absolute temperature K. 4.5.2 Measurement Method
Use the hot and cold load Y factor mid-cheek attenuator method, and its equipment configuration is shown in Figure 4. Hot load
Outdoor unit
Cold load
DC isolation circuit
Regulated power supply
Precision receiver
Signal source
Figure 4 Equipment configuration for measuring noise temperature using the Y factor intermediate frequency attenuator method for hot and cold loads The measurement steps are as follows:
a) The noise temperature of the outdoor unit should be measured at the specified frequency within the passband (at least six frequency points should be measured, and each point should be measured three times). The noise temperature measured at each frequency point is actually the average noise temperature. To ensure the authenticity of the measurement results, when measuring the noise temperature at the upper and lower limit frequency points of the outdoor unit, the local oscillator frequency of the test system should be selected as follows:26
GB/T 11298.3--1997
When the outdoor unit uses a high local oscillator frequency (3.7GHz~4.2GHz working frequency band as an example): When measuring the noise temperature at the lower limit of the passband, the system local oscillator uses a low local oscillator frequency; when measuring the noise temperature at the upper limit of the passband, a high local oscillator frequency is selected. For example, when the local oscillator frequency of the outdoor unit is 5170MHz and the intermediate frequency of the precision receiver is 30MHz, the local oscillator frequency of the precision receiver is selected to be 1440MHz when measuring the noise temperature at the lower limit of the passband, and the local oscillator frequency of the precision receiver is selected to be 1 000 MHz when measuring the noise temperature at the upper limit of the passband.
When the outdoor unit uses a low local oscillator frequency, the opposite is true. Because the noise temperature of the outdoor unit under test is determined based on its input port, the calculation is also based on the hot and cold load noise temperatures of the port. If there are transmission lines or other devices (such as waveguide isolators) between the hot and cold load output ports and the input port of the outdoor unit under test, their influence should be deducted; b) Connect the cold load to the input port of the outdoor unit and adjust the variable attenuator of the precision receiver so that the indicator points to a reading close to the full scale I. Record the reading I. and the attenuator reading A expressed in decibels. c) Connect the heat load to the outdoor unit input port, increase the attenuation of the precision variable attenuator, so that the precision receiver indicator gets the same reading, and record the attenuator value Ah at this time; d) Repeat steps b) and c) twice to get the corresponding A. and A values, calculate the corresponding Y, (dB) according to formula (1), and then use formula (2) to calculate the average value Y, in decibels.
Y, =(A -A),
According to formula (2), the Y factor is:
Y = 10g1
Equivalent noise temperature T. Calculate according to formula (4): T
Where: Th———Noise temperature of the heat load, K; T. —Noise temperature of the cold load (given), KTh- YT.
If a waveguide isolator is added for testing, its influence should be deducted, see formula (5): Ter - T(1 -
Where: L--is the true value of the waveguide isolator loss; T. ——Equivalent room temperature is the same as T in formula (4), K; Te--total noise temperature, K.
4.5.3 Result representation
Represented by curve or list.
4.6--Local oscillator frequency stability
(1)
(2)
·(3)
4.6.1 General considerations
Local oscillator frequency stability refers to the ratio of the difference between the actual output frequency of a local oscillator and the nominal frequency within the specified temperature range; the nominal frequency refers to the measured output frequency of a local oscillator at room temperature. 4.6.2 Measurement method
The measurement equipment configuration is shown in Figure 5.
Synthesizer
Measurement steps:bzxz.net
Coupler
GB/T 11298.3—1997
Waveguide conversion
Temperature test chamber
DC isolation
Figure 5 Equipment configuration for measuring the stability of a local oscillator frequency
Counter
a) Connect the equipment as shown in Figure 5 and power on the outdoor unit for 0.5h. Without starting the temperature test box, adjust the frequency synthesizer so that its frequency is within the working frequency band, input the RF signal to the outdoor unit input port through the directional coupler, and use the counter to record the frequency synthesizer's frequency fi
b) Connect the frequency counter to the outdoor unit output, record the outdoor unit's output frequency f2, then the nominal frequency of a local oscillator is: fLo=fi+f (applicable to high local oscillator); or fL=f-f (applicable to low local oscillator); c) Start the temperature test box, measure the local oscillator frequency f at each temperature point (at least 0.5h at each temperature point) within the specified temperature range, and calculate the difference with the nominal frequency;
Af = IfLo - fl
d) Find the maximum absolute value of △f IAFIm and calculate the frequency stability of the local oscillator based on this. Sm
4.6.3 Result representation
Use graphics or text description.
4.7 Local Oscillator Leakage Level
4.7.1 General Considerations
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Local Oscillator Leakage refers to the local oscillator leakage level detected at the input port of the outdoor unit, expressed in decibel milliwatts. 4.7.2 Measurement Method
The measurement equipment configuration is shown in Figure 6.
Spectrum Analyzer
Waveguide Conversion
Local Oscillator Leakage Measurement Equipment Configuration
Measure directly at the input port of the outdoor unit using a spectrum analyzer. 4.7.3 Result Representation
Describe in words.
4.8 Input Saturation Level
4.8.1 General Considerations
The input saturation level refers to the input signal level when the outdoor unit under test experiences a gain compression of 1 dB, expressed in decibel milliwatts. 28
（6）
4.8.2 Measurement method
The measurement equipment is configured as shown in Figure 7.
Signal source
Measurement steps:
Waveguide conversion
GB/T 11298.3--1997
DC isolation
Figure 7 Input saturation level measurement equipment configuration
a) Set the frequency of the signal source to the center frequency of the working frequency band; spectrum analyzer
or level meter
b) Connect the power supply to the outdoor unit under test, start the input level from -70dBm, and increase it in 1dB steps. Read the corresponding output level value of the outdoor unit and calculate the gain of the outdoor unit under test in the linear region; c) Continue to increase the input level. When the gain is compressed by 1dB, the input level value is the input saturation level. 4.8.3 Result expression
Describe in words.
4.9 Image Interference Suppression Ratio
4.9.1 General Considerations
The image interference suppression ratio is a measure of the ability of the outdoor unit to suppress image frequency signals. When the outdoor unit operates in the linear range, the ratio of the output signal level to the image signal level for the signal frequency and the image signal frequency with equal input levels is called the image interference suppression ratio, expressed in decibels.
4.9.2 Measurement Method
The measurement equipment configuration is shown in Figure 8.
Xinqin Source
Measurement Steps:
Waveguide Conversion
Figure 8 Image Interference Suppression Ratio Measurement Equipment Configuration is described using an outdoor unit with a high local oscillator as an example. Spectrum
Analyzer
a) According to the principle that the closer the image frequency interval is, the worse the image suppression ratio is, add the highest operating frequency signal fi with a level of -70dBm to the input port of the outdoor unit, and read the level value of the lowest output frequency fouL at the output port; b) Then add the signal with a frequency of f, + 2foul and a level of -70dBm to the input port of the outdoor unit, and measure the level value of fou at the output port of the outdoor unit;
c) Calculate the ratio of the two measured levels as the image interference suppression ratio. 4.9.3 Result expression
Describe in words.
4.10 Multi-carrier intermodulation ratio
4.10.1 General considerations
When two in-band carriers of specified frequencies and levels are input simultaneously, the ratio of the carrier level output by the outdoor unit to the corresponding beat level is called the multi-carrier intermodulation ratio, expressed in decibels. 4.10.2 Measurement method
The measurement equipment is configured as shown in Figure 9.
Signal source
Signal source 2
Measurement steps:
GB/T 11298.3—1997
Spectrum analyzer
Waveguide conversion
Figure 9 Multi-carrier intermodulation ratio measurement equipment configuration
DC isolation
a) 1 and 3 are connected, so that the output frequency is a certain frequency f1 within the working frequency band, and the output level is -70dBm; b) Adjust signal source 2, so that its output frequency is fz=fi+4MHz, and the output level is -70dBm (the method is the same as a), c) 1 and 2 are connected, 3 and 4 are connected, observe the two carrier levels at the output end of the outdoor unit on the spectrum analyzer, and record the carrier level value (in dBm)
d) Observe the intermodulation product levels of (fLo-f+4MHz) and (fto-f2-4MHz), and record the level value (in dBm) e) Calculate the ratio of the carrier to the intermodulation product (if the level value read is in dBm, it is the difference between the carrier level and the intermodulation product level). 4.10.3 Result representation
Use a graphic representation or a text description.
4.11 Return loss
4.11.1 General consideration
The input (or output) return loss L (dB) of the outdoor unit is a measure of the matching degree between its input (or output) impedance Z and the nominal impedance Z. The return loss L (dB) is given by formula 8). L = 20 lgl
4.11.2 Measurement method
4.11.2.1 Input port return loss
z+z.
·（8)
The equipment configuration is shown in Figure 10. The measurement method can be the sweep frequency method or the point frequency measurement method. The following measurement method is the sweep frequency method. 30
Signal source
Measurement steps:
Isolator
GB/T11298.3—1997
Short circuit breaker
Coupler
Analyzer
Figure 10 Input port return loss measurement equipment configuration DC isolation
a) Set the starting frequency of the sweep frequency signal source to the low end of the working frequency band, the ending frequency to the high end of the working frequency band, and the output level to -70dBm , and put the signal source in the frequency sweep state; b) 1 and 2 are connected, the baseline is calibrated, and stored; c) 1 and 3 are connected, and the spectrum analyzer displays another test curve in the working frequency band; d) The first curve is called out, the two curves are in the same window, and the two curves are printed out; e) Observe the two printed curves, the return loss is the worst at the point where the two curves are closest, and record the data difference here (in dB), which is the return loss of the input port. 4.11.2.2 Output port return loss
The equipment configuration is shown in Figure 11.
Signal source
Coupler
Analyzer
DC isolation
Note: The return loss of the DC isolation circuit must be above 20dB. 2o
Figure 11 Output port return loss measurement equipment configuration Measurement steps:
a) Open the 1 end in Figure 11, adjust the sweep signal source, make the starting frequency the low frequency of the intermediate frequency band, and the ending frequency the high frequency of the intermediate frequency band, and make it in the sweep state, calibrate the 0dB loss line on the spectrum analyzer, and store it; b) Connect 1 and 2, and then display another test curve in the working frequency band on the spectrum analyzer, and call out the upper curve, so that the two curves are in the same window, and print out both curves at the same time; c) Observe the printed curve; the return loss is the worst at the point where the two curves are closest, and record this difference (in decibels), which is the return loss of the output port.
The point frequency measurement method is to measure a data with the spectrum analyzer every time a signal source frequency is changed, and the measurement steps are the same as 4.11.2.1 and 4.11.2.2.
4.11.3 Result Representation
Use curve or text description.
4.12 Gain Stability
General Consideration
GB/T11298.3—1997
Gain stability refers to the change of gain over time at a specified frequency within the passband. 4.12.2 Measurement Method
Can use the swept frequency method or the point frequency measurement method. Regardless of which method is used, care should be taken to keep the output level of the swept frequency signal source or the continuous wave signal source constant. If it changes during the measurement process, it should be corrected. The swept frequency measurement method is in accordance with 4.2.2 Spectrum Analyzer Sweep Frequency Measurement Method. The equipment configuration of the point frequency measurement method is shown in Figure 12. Signal source 1
Measurement steps:
Waveguide conversion
DC blocking
Figure 12 Gain stability measurement equipment configuration
It is carried out at a certain frequency within the passband. The center frequency is used as an example for explanation below. Precision
Receiver
Signal source 2
a) Adjust the frequency of signal source 1 to the center frequency of the working frequency band, adjust the output level to -70dBm and add it to the input of the outdoor unit;
b) Adjust the frequency of signal source 2 to the center frequency of the output frequency, adjust the level to +5dBm, and add it to the local oscillator entrance of the precision receiver mixer to ensure that the output frequency after mixing is 30MHz and the level is within the receiving range of the precision receiver;c ) Use a precision receiver to measure the level value, change the value of the precision receiver attenuator so that the indicator points to 60, and record the attenuator reading A, expressed in decibels:
d) Keep the outdoor unit powered on during the specified measurement time, repeat steps a, b, and c once every half an hour, and record the attenuator readings A, AAA, A each time
e) Record the value of △A=A2-AiA-A,,A,-A,., IAA|max, which is the gain stability. 4.12.3 Result Representation
Use a curve or text description.
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