GB/T 11299.8-1989 Satellite communication earth station radio equipment measurement methods Part 2: Subsystem measurements Section 4: Upconverters and downconverters
Some standard content:
National Standard of the People's Republic of China
Methods of measurement for radio equipment used in satellite earth stationsPart 2.Measurements for sub-systemsSection Four-Up and down convertersThis standard is the first in the series of standards "Methods of measurement for radio equipment used in satellite earth stations" Subject content and scope of application
GB11299.8---89
This standard specifies the measurement of electrical performance of up and down converters in transmitters and receivers of satellite communication earth stations and is applicable to the subsystem shown in Figure 1 of the "General Principles" of this series of standards GB11299.1 "Methods of measurement for radio equipment used in satellite earth stations". 2 Overview
2.1 Upconverter
The upconverter is a subsystem of the transmission chain, which converts the intermediate frequency signal (e.g. 70MHz) into the radio frequency signal (e.g. 6GIHz). Figure 1 shows a typical block diagram of the upconverter with sub-conversion. In some cases, one or more mixing may be used to facilitate frequency conversion.
The upconverter shown in Figure 1 mainly consists of an intermediate frequency stage, a mixer, a local oscillator and a radio frequency stage. A filter is added after the mixer to suppress the local oscillator signal and other spurious signals appearing at the output of the upconverter. The intermediate frequency equalizer is used to compensate for the amplitude and group delay characteristics of the upconverter, while the separately added intermediate frequency amplitude equalizer and group delay equalizer are used to equalize the earth station transmission characteristics and the pre-correction satellite group delay characteristics, respectively. The variable attenuator is used to adjust the intermediate frequency signal level. 2.2 Downconverter
The downconverter is a subsystem of the receiving chain, which converts the RF signal (e.g. 4GHz) into an intermediate frequency signal (e.g. 70MHz). Figure 2 shows a typical block diagram of a downconverter with a single frequency conversion, but in some cases, one or more mixing may be used to facilitate frequency conversion.
The downconverter shown in Figure 2 mainly consists of an RF stage, a mixer, a local oscillator and an intermediate frequency stage. A filter is added after the mixer to suppress the local oscillator signal and other spurious signals appearing at the output of the downconverter. The intermediate frequency equalizer is used to compensate for the amplitude and group delay characteristics of the downconverter. The equalization of the receiving chain is usually completed by a separate equalizer. For changes in the RF input level, the automatic gain control (AGC) can maintain a constant intermediate frequency level. 2.3 Frequency relationship
In the up-converter or down-converter, the following can be adopted: fu - Jo + fi
f=fia - f1
Approved by the Ministry of Electronics Industry of the People's Republic of China on March 1, 1989. (2)
Implemented on January 1, 1990
In the formula; f.—RF signal frequency;
—local oscillator frequency;
-----IF signal frequency.
GB11299.8—89
Note that in equation (2) the modulated sidebands have been switched. This situation may not meet the technical requirements of the existing system. It should also be noted that the mixer may be parametric. In this case, the local oscillator is usually called a "pump source". 3 Input and output return loss
The input return loss of the upconverter is measured at the intermediate frequency, while its output return loss is measured at the radio frequency. The input crosstalk loss of the downconverter is measured at the radio frequency, while its output return loss is measured at the intermediate frequency. For radio frequency measurements, refer to Section 4 "Impedance (admittance) measurement" of Part 1 of this series of standards. For intermediate frequency measurements, refer to Section 3 "Return loss" of Measurement within the intermediate frequency range of GB11299.3 of this series of standards.
Specially explain the following points:
a. For input return loss measurement, the nominal input level of the device under test may be too small. In this case, a higher level can be used (for example, a signal level 10-15dB lower than the local oscillator level is input to the nonlinear device in the mixer), but it must be ensured that the measurement result does not change when the level is slightly reduced (for example, 3dB). b. Pay attention to exclude the useless signals brought into the measurement, especially those from the local oscillator. C. The power of the local oscillator should meet the nominal value. 4 Input and output level or power
According to Chapter 5 "Level and Gain" of "Measurements in the RF Range" of this series of standards GB11299.2 and Chapter 4 "Input and output level" of "Measurements in the IF Range" of this series of standards GB11299.3. 5 Gain
According to Chapter 5 "Level and Gain" of "Measurements in the RF Range" of this series of standards GB11299.2. Note: 1) The input frequency and output frequency are different, which needs to be considered in the configuration of the measuring equipment. 2) The substitution technique can be used for measurement, but it is rarely used. 5.1 Gain instability
See Chapter 4 "Gain instability" of Section 3 of Part 2 of this series of standards "Measurements in the IF Range". 5.2 Gain compression
5. 2. 1 Definition
Gain compression is the difference between the gain measured at low level and the gain measured at maximum rated output in decibels. 5.2.2 Measurement method
The gain defined above is measured at different input signal levels, and the gain compression is calculated from the measured values. To measure small gain compression, the test equipment used should be of high precision and high stability. If a filter is used in the measurement, its insertion loss should be considered in the measurement result. When measuring, the desired signal can be selected with a frequency-selective level meter. In this way, the gain compression value can be obtained from the input signal. The relationship curve between the output level and the input level can also be obtained according to Chapter 5 "Level and Gain" of GB11299.2 "Measurements within the RF Range" of this series of standards.
Note: (①) If there is an automatic gain control, its control switch should be turned off. At the nominal input level, the intermediate frequency gain should be manually adjusted to obtain the nominal output level. ② In order to avoid errors caused by power fluctuations, two power meters should be used to read the readings at the same time. One is connected to the input end and the other is connected to the output end. Using a differential measurement device can make the measurement accuracy of gain compression higher than that of using two power meters. 5.2.3 Result Representation
The measurement results are best expressed as a curve of the relationship between power gain and input power. When the measurement results are not represented graphically, they should be expressed as follows:
GB11299.8—89
*When the input (or output) level is ×XdBm, the gain compression is ××dB\. 5.2.4 Details to be specified
When this measurement is required, the following shall be included in the equipment specifications: Input level;
Output level;
℃. Permissible gain compression.
6 Automatic gain control (AGC)
If automatic gain control is used, its characteristics can be checked according to this series of standards GB11299.3 "Measurements within the intermediate frequency range": 7 Differential gain
According to this series of standards GB11299.3 * Measurements within the intermediate frequency range \ Chapter 9 \ Differential gain and differential phase characteristics". 8 Differential phase
According to this series of standards GB11299.3 \ Measurements within the intermediate frequency range "Chapter 9 "Differential gain and differential phase characteristics" 9 AM/PM conversion coefficient
This measurement is generally not performed in downconverters. 9.1 Definitions
The amplitude modulation/phase modulation (AM/PA) conversion factor is defined as: for a given input frequency, the first-order derivative of the output signal phase with respect to the input signal level, expressed in degrees/decibels.
9.2 Measurement Methods
The AM/PA conversion factor can be measured by either static or dynamic methods. If the upconverter under test has an automatic gain control, it should be turned on during the measurement.
9.2.1 Static Method
The measurement equipment is shown in Figure 3. The change in phase of the output signal of the upconverter under test is compared with the phase of the output signal of an upconverter with known performance (the "test" upconverter). A suitable phase meter, such as a network analyzer or a vector voltmeter, is used to detect the phase change of the output signal when the input signal level changes by a specified amount (for example, 1.0 dI3). The static method can only be used when the upconverter under test and the test upconverter use the same local oscillator. Before measurement, the phase shift error caused by the level change of the measuring equipment itself (especially the measuring attenuator and phase meter) should be determined. 9.2.2 Dynamic method
The configuration of the measuring equipment is shown in Figure 4. The measurement method is in accordance with the provisions of Chapter 9 "Amplitude modulation/phase modulation conversion coefficient" of this series of standards GB11299.2\Measurement within the radio frequency range".
The residual amplitude modulation/phase modulation conversion coefficient of the measuring equipment including the test downconverter should not be obvious. 9.3. Result Expression
The measurement result shall be expressed in degrees/decibels, and preferably in a graphical representation of the numerical relationship between the amplitude modulation/phase modulation conversion coefficient and the input signal level at each given frequency.
9.4. Details to be specified
When this measurement is required, the equipment specifications shall include the following: a. The test method used (9.2.1 or 9.2.2); the level and frequency of the input intermediate frequency signal;
the tolerance value of the amplitude modulation/phase modulation conversion coefficient.
10 Amplitude/Frequency Characteristics
GB11299.8-89
According to this series of standards GB11299.2 "Measurements in the radio frequency range" Chapter 6 \ Amplitude/Frequency Characteristics". In the above clauses, the input level is assumed to be constant. For frequency converters with automatic gain control, the control must be disconnected and the gain must be adjusted slightly to achieve the nominal output level. Then, the measurement is performed at the nominal level. Note: 1) A suitable signal generator and detector are required. The signal generator can be The measurement method of the frequency-beating type and the nonlinear frequency converter is under consideration. 11 Group delay/frequency characteristics
According to this series of standards GB11299.2 "Measurements in the radio frequency range" Chapter 7 "Group delay/frequency characteristics\ and Part 1: Section ~ Measurements in the intermediate frequency range" Article 8 "Group delay/frequency characteristics" Note: If the measuring equipment works at the intermediate frequency, it is necessary to use a suitable test upconverter or test downconverter. It is important that the test converter has sufficient bandwidth and linearity and a known small group delay change. 12 Selectivity
12.1 Definition
Selectivity is the frequency discrimination ability of the receiver (here refers to the downconverter). It can distinguish the useful signal from the useless signals of other frequencies that coexist with it through frequency-related selection. 12.2 Measurement method
The measurement equipment is configured as shown in Figure 5. The signal generator (2) is adjusted to the nominal input frequency of the downconverter under test to simulate a useful signal: The signal generator (1) simulates an unwanted signal. The useful signal or unwanted signal level is determined by attenuator (2) and attenuator (1) respectively: If necessary, a level meter can be connected to the "RF input" mark to calibrate the level each time a measurement is made. The frequency of the signal generator (1) is changed and the output signal level caused by the signal generator (1) is measured with a calibrated spectrum analyzer. At the same time, the unwanted signal level at the "RF input" is kept constant or at a specified value at each frequency. 12.3 Result presentation
The measurement results are presented in a table or graph. It is the difference between the output level values of the useful signal and the unwanted signal (in decibels) as a function of the unwanted signal frequency (within the specified frequency range) at the specified input levels of the useful signal and the unwanted signal. 12.4 Details to be specified
When this measurement is required, the equipment specifications should include the following: a. Useful signal Input level of the signal and the unwanted signal; the frequency range of the measurement;
C. The minimum selectivity characteristics allowed (the functional relationship between the level and the frequency or the allowable range of the level of the relevant frequency is given in a predetermined frame).
13 Spurious output signal (including harmonics)
According to this series of standards GB11299.2\Measurement within the radio frequency range" Chapter 10 "Spurious signals (including harmonics)" Note: () If the dynamic range of the spectrum analyzer is not enough, insert an appropriate band-stop filter to reduce the input carrier level ② Pay attention to prevent the local oscillator signal from entering the spectrum analyzer, for example, an appropriate filter can be inserted. 14 Interference radiation
is under consideration.
15 Intermodulation distortion
According to Chapter 8 "Multi-carrier intermodulation ratio" of this series of standards GR11299.2\Measurements in the radio frequency range". 86
16 Residual angle modulation noise
16.1 Definition and general considerations
CB11299.8--89
When a pure sinusoidal signal of nominal frequency and level is added to the input of the device under test, its output signal will contain additional noise, which is defined as residual frequency modulation or phase modulation noise. After demodulation, it is usually measured every 4kHz (or 3.1kHz) bandwidth within the baseband frequency range and can be expressed as an equivalent root mean square frequency deviation (Afm). Residual Phase modulation noise is defined as the ratio of the equivalent RMS frequency deviation (H) due to residual FM noise to the baseband frequency (H). Residual phase modulation noise can be expressed in radians (RMS). The residual phase modulation noise expressed in degrees (RMS) can be obtained by multiplying the value expressed in radians (RMS) by 57.3. 16.2 Downconverter measurement method
The typical measurement configuration is shown in Figure 6. Before measurement, the equipment must be calibrated as follows. 16.2.1 Calibration
The sensitivity of the frequency demodulator is calibrated using a frequency signal generator (A). At a specified frequency, it is frequency modulated with a known modulation index according to this series of standards GB11299.9\Frequency demodulator". When the intermediate frequency carrier output by the low noise signal generator (B) is applied to the demodulator input, the residual angle modulation noise level can be measured at the demodulator output using a frequency selective level meter of known bandwidth. 16.2.2 Measurement
To measure the residual angle modulation noise, the RF signal generator outputs a sinusoidal signal of a specified frequency, the level of which is the maximum value of the nominal operating level, which is added to the input of the device under test, and the frequency-selective level meter is connected to the output. The frequency-selective level meter is adjusted to each baseband frequency in turn to perform noise measurement and residual angle modulation noise measurement. The measured noise value includes the noise caused by the RF signal generator and demodulator, which should be lower than the noise level to be measured. 16.3 Measurement method of frequency converter
The typical measurement configuration is shown in Figure 7. It is important to ensure that the intermediate frequency signal generator, the frequency converter and the demodulator under test are all low-noise devices. Before measurement, the test equipment must be calibrated as required below. 16.3.1 Calibration
Use a signal generator (A) that can perform frequency modulation at a specified frequency with a known modulation index to calibrate the sensitivity of the demodulator. According to this series of standards GB11299.8*Frequency demodulator. When the carrier output by the low-noise signal generator (B) is added to the input of the measuring device, the residual angular modulation noise of the device (including the mixer, intermediate frequency amplifier and demodulator) can be measured by a frequency-selective level meter with a known bandwidth. 16.3.2 Measurement
In order to measure the residual noise, the low-noise intermediate frequency signal generator outputs a sinusoidal signal of a specified frequency with a level equal to the maximum value of the nominal working level. To the input of the device under test, the frequency-selective level meter is connected to the output. The frequency-selective level meter is adjusted to each baseband frequency in turn to perform noise measurement and residual angle modulation noise measurement. The measured results include the noise of the test equipment, which should be lower than the noise level to be measured. 16.4 Result Representation
The result of the residual angle modulation noise measurement can be expressed as a function curve of the equivalent root mean square frequency deviation (△fn) within each 4kHz (or 3.1kHz) baseband bandwidth versus the baseband frequency.
16.5 Details to be Specified
When this measurement is required, the equipment technical requirements should include the following: a. . The level and frequency of the unmodulated carrier;
b. The baseband frequency and bandwidth of the noise to be measured; the maximum allowed noise level.
17 Residual AM noise
17.1 Definition and general considerations
GB11299.8--89
When a sinusoidal signal of nominal frequency and level is applied to the input of the device under test, the output signal may be amplitude modulated by the noise generated inside the device. This unwanted modulation is defined as residual AM noise. After demodulation, this noise is measured in kHz (or 3.1kHz) bandwidth within the baseband frequency range.
17.2 Measurement Measurement method
The typical configuration for measuring amplitude modulation noise is shown in Figure 8. Care should be taken to ensure that the bandwidth of the detector output is wide enough. Before measurement, the measuring equipment needs to be calibrated as follows.
17.2.1 Calibration
Put switches S and S2 in the "calibration" position (Figure 8), and connect the output of the signal generator (B) to the input of the frequency converter under test. Adjust the signal generator (B) to the specified frequency and nominal operating level, and then the signal generator (B) is amplitude modulated at an appropriate frequency (for example, 1.0MHz), and the output signal of the frequency converter under test is displayed on a spectrum analyzer with appropriate frequency resolution. Adjust the modulation signal level until the spectrum analyzer shows that each sideband level is not affected by residual noise (for example, 20 dB higher than the residual noise level), and then record the difference L\xdB" between the amplitude of the larger sideband and the carrier amplitude. Turn switch S,Put it in the "measure" position, connect the output signal to the detector and the frequency-selective level meter. When the frequency-selective level meter is tuned to the modulation frequency of the test signal, a reference reading is obtained. Note: Because the power measured by the frequency-selective level meter is in both sidebands, the level read will be 3 dB higher than the \xdB\ obtained by comparing the single sideband with the carrier. 17.2.2 Measurement
Put switches S1 and S2 in the "measure" position and measure the level of residual AM noise by appropriately tuning the frequency-selective level meter at the specified baseband frequency starting from 4 kHz.
If the bandwidth of the frequency-selective level meter is not 4 kHz (or 3.1 kHz), its actual bandwidth must be taken into account. For frequency bands below 4 kHz, place switch S1 in Figure 8 at the 4 kHz low-pass filter and the RMS voltmeter for measurement. 17.3 Representation of results
The measurement results are best presented as a curve showing the number of decibels below the carrier level of the residual AM noise as a function of the baseband frequency.
When the measurement results are not presented graphically, they shall be presented as follows: At all baseband frequencies between ××MHz and ××MHz, the residual AM noise within any -1kHz (or 3.1kHz) bandwidth is ××dB lower than the carrier level".
17.4 Details to be specified
When this measurement is required, the equipment technical requirements shall include the following: a. The frequency and level of the unmodulated carrier;
b. The baseband frequency and bandwidth of the measured noise; c. The maximum allowable noise level.
18 Noise coefficient
See this series of standards GB11299.5*Noise temperature measurement". 19Local oscillator frequency
Measured at the monitoring end of the local oscillator, which is generally present in the up-converter and down-converter. The measurement method is in accordance with this series of standards GB11299.2 "Measurements within the radio frequency range". The measurement is generally carried out within the specified time interval and under the standard environmental conditions given in Part - of this series of standards. Of course, other environmental conditions can be specified if necessary. 88
Filter
Intermediate signal
Generator
Amplifier
GB11299.8
Amplifier
Mixer
Local oscillator frequency
Oscillator
Up-converter (sub-mixing) typical block diagram
Mixer
Local oscillator frequency
Oscillator||t t||Amplifier
Filter
Filter
Figure 2 Typical block diagram of downconverter (single mixer) Test
Upconverter
Distributor
Attenuator
Upconverter
Figure 3 Typical equipment configuration for measuring the AM/PM conversion coefficient of the upconverter using the static method Test Delay network
Test frequency
Modulation Controller
Baseband differential gain
Measurement device
Upconverter under test
Amplifier
Downconverter under test
Test frequency
Decoder
Typical equipment configuration for dynamic measurement of upconverter AM/PM conversion coefficients To
RF signal
Generator (1)
Useless signal|| tt||RF signal
Generator (2)
(useful signal)
Radio signal
Generator
Low noise intermediate frequency
Signal generator
Radio frequency transformer
Attenuator (1)
RF variable
Attenuator (2)
GB11299.8
Directional coupler
RF input
Downconverter
Figure 5 Equipment configuration for measuring downconverter selectivity Tested
Downconverter
Baseband signal
Generator
Attenuator
Intermediate frequency signal
Generator (B)
Intermediate frequency signal
Generator (A)
Demodulator
Intermediate frequency ( Figure 6 Measuring the residual angle modulation noise of the downconverter Equipment configuration Under test Upconverter Attenuator Generator (B) Mixer Oscillator Baseband signal Generator Amplifier Under test Converter Generator (A)
Intermediate frequency
Analyzer
Level meter
Demodulator
(Frequency modulation)
Analyzer
Figure 7 Equipment configuration for measuring residual angle modulation noise of upconverter Frequency selection
Electric Hua meter
Low noise output signal
Generator (B)
AM input
o Calibration||tt ||Additional instructions:
Frequency converter
Baseband signal
Generator (A)
GB11299.8—89
Spectrum analyzer
oCalibration
Q measurement
Variable attenuator
Detector
Figure 8 Equipment configuration for measuring residual AM noise This standard was drafted by the First Research Institute of the Ministry of Posts and Telecommunications. Q
Low-pass filter
Electric watch
Root mean value
Voltmeter8
Directional coupler
RF input
Down converter
Figure 5 Equipment configuration for measuring down converter selectivity Tested
Down converter
Baseband signal
Generator
Attenuator
Intermediate frequency signal
Generator (B)
Intermediate frequency signal
Generator (A)
Demodulator
Intermediate frequency (FM)
Analyzer
Figure 6 Measuring the residual angle modulation noise of the downconverter Equipment configuration Tested
Upconverter
Attenuator
Generator (B)
Mixer
Oscillator
Baseband signal
Generator
Amplifier
Under test
Converter||t t||Generator (A)
IF
Analyzer
Level meter
Demodulator
(FM)
Analyzer
Figure 7 Equipment configuration for measuring the residual angle modulation noise of the upconverter Frequency selection
Electric Hua meter
Low noise output signal
Generator (B)
AM input
oCalibration| |tt||Additional instructions:
Frequency converter
Baseband signal
Generator (A)
GB11299.8—89
Spectrum analyzer
oCalibration
Q measurement
Variable attenuator
Detector
Figure 8 Equipment configuration for measuring residual AM noise This standard was drafted by the First Research Institute of the Ministry of Posts and Telecommunications. Q
Low-pass filter
Electric watch
Root mean value
Voltmeter8
Directional coupler
RF input
Down converter
Figure 5 Equipment configuration for measuring down converter selectivity Tested
Down converter
Baseband signal
Generator
Attenuator
Intermediate frequency signal
Generator (B)
Intermediate frequency signal
Generator (A)
Demodulator
Intermediate frequency (FM)
Analyzer
Figure 6 Measuring the residual angle modulation noise of the downconverter Equipment configuration Tested
Upconverter
Attenuator
Generator (B)
Mixer
OscillatorwwW.bzxz.Net
Baseband signal
Generator
Amplifier
Under test
Converter||t t||Generator (A)
IF
Analyzer
Level meter
Demodulator
(FM)
Analyzer
Figure 7 Equipment configuration for measuring the residual angle modulation noise of the upconverter Frequency selection
Electric Hua meter
Low noise output signal
Generator (B)
AM input
oCalibration| |tt||Additional instructions:
Frequency converter
Baseband signal
Generator (A)
GB11299.8—89
Spectrum analyzer
oCalibration
Q measurement
Variable attenuator
Detector
Figure 8 Equipment configuration for measuring residual AM noise This standard was drafted by the First Research Institute of the Ministry of Posts and Telecommunications. Q
Low-pass filter
Electric watch
Root mean value
Voltmeter
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