GB/T 11299.2-1989 Satellite communication earth station radio equipment measurement methods Part 1: Measurements common to subsystems and subsystem combinations Section 2: Measurements in the radio frequency range
Some standard content:
National Standard of the People's Republic of China
Methods of measurement for radio equipment used in satellite earth stationsPart 1: Measurements common to sub-systemsand combinations of sub-systemsSection Two-Measurements in the r. f, rangeThis standard is one of the standards in the series of "Methods of measurement for radio equipment used in satellite earth stations for satellite communication"GB11299.289
IEC 510-1-2(1984)
This standard is equivalent to the International Electrotechnical Commission standard IEC510-1-2 (1984) "Methods of measurement for radio equipment used in satellite earth stations for satellite communicationPart 1: Measurements common to sub-systemsand combinations of sub-systemsSection Two-Measurements in the r. f, range". Subject content and scope of application
This standard specifies the measurement methods for transmitting equipment and receiving equipment in satellite earth stations for satellite communication within the r. f, range. This standard is applicable to both sub-systems and combinations of sub-systems. 2 Overview
It is not possible to describe comprehensively the precautions necessary to obtain the required accuracy in all the types of measurements described below, but some general concerns should be noted. It should not be ignored that there may be spurious signals (including harmonics) at the test signal input terminals, which may interfere with the operation of the test equipment and may also interfere with the operation of the system or subsystem under test. Although the amplitude of these spurious signals is not sufficient to affect the test equipment, consideration should still be given to removing these unwanted signals at the test terminals because their presence may change the RF characteristics of the test, such as the effect of heating. The mechanical mounting of components (including ferrite isolators and circulators) and the position of RF shielding should not be changed unless it is certain that the overall performance after the changes is representative of the performance of the system or subsystem under test. In the following measurement methods, no requirements are mentioned to protect the measurement equipment from possible RF interference. When using the swept frequency method, the passband of the test receiver (frequency selective amplifier, amplitude detector and oscilloscope) should be 50 to 100 times the sweep frequency, depending on the waveform of the sweep multiple. The tester should arrange the measurement equipment as needed to keep the measurement error within the allowable range. When presenting the measurement results, a diagram of the actual measurement equipment configuration used should be given, with the load, isolator, low-pass filter and other devices marked in the diagram. In addition, the models of the various measuring instruments used and the rated power of the attenuator should be listed. When presenting the measurement results, the measurement accuracy and the source of error should be stated, and other necessary explanations should be made to avoid ambiguity in the interpretation of the results. 3 Carrier frequency
3.1 Definition and general considerations
In satellite communication systems, the output of the device under test usually has more than one carrier frequency. The carrier frequency is the frequency at which the spectrum of the RF signal is modulated by the pseudo signal.
Approved by the Ministry of Electronics Industry of the People's Republic of China on March 1, 19898
Implementation on January 1, 1990
GB11299.2—89
In the absence of a baseband test signal, for example, when the carrier frequency is modulated by a diffuse multiple of the quotient modulation index, the spectral line corresponding to the carrier frequency may not be easily distinguished on a spectrum analyzer. In this case, assuming that the averaging interval is long enough, for example, 100 times the period corresponding to the lowest modulation rate, the carrier frequency can be defined as the average number of positive or negative zero crossings per second. This standard recommends two methods for measuring the RF carrier frequency. The first method is applicable to unmodulated RF carriers; the second method is applicable to carriers modulated by sinusoidal baseband test signals. The measurement of the carrier frequency of a radio modulated by a working baseband signal (such as frequency division multiplexing telephone or television) is considered.
The carrier frequency can be measured at the RF output of the radio transmitter or after transmission through some subsystems. In this case, different measurement values will be obtained due to the error of the local oscillator frequency. The frequency of the local oscillator can also be measured by the described method. 3.2 Measurement method
3.2.1 Unmodulated RF carrier
The general equipment configuration for measuring the unmodulated RF carrier frequency is shown in Figure 1. The instrument is required to have a filter only when there are spurious signals. Only when the frequency meter cannot cover the specified electrical half range and/or frequency Range, the need for a transmitter and/or attenuator and frequency converter is only required! Before any measurement, both the device under test and the measuring equipment should be thermally stabilized, and if there is an energy dissipation device, it should be stopped.
Then, read the digital frequency meter once every interval, for example seconds, and the interval time will be selected by the gate time of the instrument used.
In addition, the recorder shown in Figure 1 can be used to record the values of the digital frequency meter. If there are 100 counts, it is enough, but, usually in the case of low frequency, the number of counts depends on whether the noise exists and whether the noise is sufficient to modulate the signal or superimposed on the signal. Usually, the analysis of the statistical series averaged over several measurement intervals will provide repeatable results. Note: () When the RF carrier is a base The above method can also be used when the carrier is modulated by a signal, assuming that the digital frequency meter does not cause errors. These errors depend on the modulation signal frequency and frequency offset. The average interval of the digital frequency meter should exceed 100 times the period corresponding to the modulation frequency. (2) In a multi-carrier system, each carrier should be measured separately, and the other carriers should be either turned off or filtered out with an appropriate filter. 3.2.2 Modulated RF carrier
The measurement equipment configuration of the modulated RF carrier is shown in Figure 2. This measurement method can be used to determine whether the carrier frequency has changed significantly after modulation. In order to identify the spectral line corresponding to the carrier frequency with the required accuracy, the modulation signal used in this measurement should be appropriately selected. The measured signal (whether modulated or unmodulated) is displayed at a certain resolution On a spectrum analyzer, only the center of the spectrum needs to be displayed. Then adjust the frequency of the reference oscillator until a signal of that frequency appears on the screen and coincides with the carrier frequency of the signal being measured. In this way, the frequency of the reference oscillator is the frequency of the carrier being measured and can be read on the digital frequency meter. Note: If the method is used, the measurement can also be performed at the intermediate frequency. 3.2.3 Result Representation
When the direct measurement method (3.2.1) is used, the readings of the digital frequency meter can be recorded manually or automatically as a function of time. The gate time of the selected digital frequency meter should be given. The indirect measurement method (3.2.2) is not suitable for automatic recording of readings, but can be recorded manually to express the RF frequency as a function of time, modulation level, modulation frequency or any other corresponding variable. 3.2.4 Details to be specified
When this measurement is required, the equipment technical specifications should include the following: single or multiple carrier frequencies;
b. Tolerance;
modulated signal for test.
4 Impedance (or Admittance)
4.1 Definition and General Considerations
The input and output impedance (admittance) of equipment used in telecommunication systems can usually be expressed in terms of return loss relative to the nominal impedance of the device under test, or in terms of voltage standing wave ratio (VSWR). The return loss (L) of an impedance (Z) relative to its nominal impedance (2.) is given by: Z+Z(dB)
L= 20 log10|2=z
or by:
L=20logno
where: 0 is the voltage reflection coefficient of the impedance (Z) relative to its nominal value (Z.), i.e.: z-2e
p=z+z.
The relationship between return loss (L) and voltage standing wave ratio (VSWR) is as follows: I. 20 log1oVswR =
VSWR + 11
4.2 Measurement method
The following measurement method is suitable for measuring the return loss of linear devices. Measurements of nonlinear devices or measurements in the presence of external signals require special methods that are not specified here. Measurements can be made using the sweep frequency method or the point-by-point measurement method. t
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The point-by-point measurement method requires a large number of individual measurements and is time-consuming. Both measurement methods can be used using the measurement line technique or the reflectometer technique. When the best measurement equipment is used, the measurement accuracy of the voltage standing wave ratio is within about 0.01. 4.2.1 Measurement line point-by-point measurement method
The typical measurement equipment configuration of the measurement line method is shown in Figure 3. The device under test should have a linear characteristic at the signal level required by the voltage standing wave ratio indicator.
The signal generator is usually amplitude modulated, and the moving probe includes an adjustable or broadband diode detector. The voltage standing wave ratio indicator is usually a frequency-selective voltmeter that is tuned to the modulation frequency, for example 1 to 200 kHz, and the measurement should be performed over the entire RF frequency band of interest.
4.2.2 Measurement line swept frequency measurement method
The typical measurement line swept frequency measurement method is shown in Figure 4. The swept frequency generator is usually amplitude modulated, and the moving probe includes a broadband diode detector. There is a detector at the output of the audio amplifier, which is tuned to the modulation frequency. The voltage standing wave ratio indicator can be an oscilloscope, preferably a storage oscilloscope, or an XY recorder. The measurement equipment is calibrated using a mismatch load with a known mismatch value. The horizontal scan of the oscilloscope corresponds to the frequency scan of the generator, and the measurement is performed as follows: the detector moves at least half a wavelength at the lowest RF frequency, and the frequency scan should cover the entire RF band of interest. At any given RF frequency (corresponding to a given point on the horizontal axis), the ratio of the maximum and minimum amplitudes of the displayed envelope given by the calibration line is the voltage standing wave ratio at that frequency. 4.2.3 Swept frequency reflectometer method
The typical measurement equipment configuration of the swept frequency reflectometer method is shown in Figure 5. A four-port directional network is used to obtain samples of the incident power and the reflected power, and the amplitude of the reflection coefficient at each frequency is measured. In order to calibrate the measurement equipment, a short circuit is used to replace the device under test, and the attenuator is adjusted to simulate a known return loss, for example, 126dB3 attenuation corresponds to 26dB return loss. This calibration method is preferable to the method that requires the knowledge of the detection law. If the incident wave level is not constant in the measured frequency band, the calibration should be adjusted during calibration. The calibration line is recorded under the relevant conditions. Note: (1) The degree to which the directivity of the directional network exceeds the measured return loss determines the achievable accuracy. For example, 40 dB directional performance enables the measurement accuracy of the measured 26c1310
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wave loss to reach 1.6~+1.9 dB. A reflectometer that can measure both amplitude and phase can be used to display the impedance circle diagram. 4.3 Results presentation
The measurement results shall be presented as a curve or a graphic photograph of an oscilloscope with a scale or as a line graph drawn by an XY recorder. When the results are not presented graphically, they shall be presented as follows: * Return loss greater than 26 dB in the frequency range of 6.1 to -6.2 GHz" The maximum error of the test results in each case shall be given. 4.4 Details to be specified
When this measurement is required, the following shall be included in the equipment specifications: a.
Nominal impedance: ||tt ||Minimum allowable return loss;
Frequency range.
5 Level and gain
5.1 Definitions
The definitions of level, power gain, insertion gain (or loss) and isolation used in this standard are as follows: 5.1.1 Level
In satellite communication earth stations, for radio frequency, level usually refers to power. The input level is defined as: the power delivered to the input of the device under test by a signal generator whose output impedance is equal to the nominal impedance (Z . ) are matched. Note: If the impedance of the device under test is not matched to that of the generator, the power delivered to the device under test will not be the maximum value. The output level is defined as the power output by the device under test to a load that matches the nominal impedance of the output port of the device under test. 5.1.2 Power Gain
The power gain of a device or subsystem is defined as the ratio of the output level to the input level. If the device under test is nonlinear, the power gain condition should be indicated, for example, saturated power gain or small signal power gain. If the power gain expressed in decibels is a negative number, the sign should usually be changed and it should be called a loss. Note: For the definition of antenna power gain, refer to Section 2 of Part 2 of this series of standards "Antenna (including feed network)". 5.1.3 Insertion Gain
The insertion gain of a device or subsystem is defined as the ratio of the power absorbed when the load is directly connected to the actual signal source (P,) to the power absorbed when the same load is connected to the same signal source through the device under test (P,). The insertion gain expressed in decibels is:
10 log1oP
If the insertion gain expressed in decibels is a negative number, its sign is usually changed and it is called "insertion loss". 5.1.4 Isolation (between two ports of a device) 4)
The isolation between the two ends of a device is defined as the ratio (in decibels) of the level of the incident wave at one port to the level of the incident wave leaking out of the other port when all ports are connected to the nominal impedance. 5.2 Measurement method
The power level is measured with a power meter, sometimes with a nominal impedance The impedance of the diode is measured with a calibrated diode detector. The diode is usually mounted in a bracket that is used to achieve matching and obtain a uniform frequency response over a wide RF bandwidth. However, the detector sensitivity is not high and requires no significant interference signals to obtain the highest accuracy. Instructions for use:
1 The original text is incorrectly 101og yuan
GB11299.289
The actual impedance of the RF power meter measurement head is close to its nominal impedance. These measurement heads are very suitable for measuring the power of the measured end! The power meter can measure power from less than microwatts to several watts. If higher powers are encountered, precision attenuators and/or calibrated directional couplers with corresponding power ratings can be used to expand the range. When higher sensitivity is required or there are stray signals at the measurement port, other methods such as frequency-selective level meters or properly calibrated spectrum analyzers can be used.
Note: When the measured signal passes through a waveguide, mode conversion may occur, that is, part of the power is converted to other modes other than the main mode. In this case, a mode converter is used to ensure that the total power of the RF signal is measured. However, the main mode power received is usually sufficient (see 5.3) 5.2.1 Input level
The level of the input test signal should be obtained on a load with nominal positive impedance (7.). The output of the signal generator is directly connected to the input end of the device under test without further level adjustment. The return loss of the load relative to the nominal impedance (Z.) should be better than 30lB. Note: When using advanced instruments, the above steps may not be required. These instruments are usually calibrated with an electromotive force or potential difference meter at both ends of the matching load. 5.2.2 Output level
5.2.2.1 Low level measurement
Connect a high-sensitivity and high-selectivity receiver with a carrier level meter to the measured end through a matching variable attenuator! . To ensure that the receiver is not saturated, the level meter reading should increase as the input signal level changes as the attenuation of the attenuator is reduced.
Then adjust the attenuator to obtain the appropriate level meter reading and record the value. Replace the device under test with a signal generator with a known output power and tune the generator to the same frequency as the receiver. Adjust the precision variable attenuator (which can be internal or external to the generator) so that the level meter reading is the same as the reading recorded above. At this time, the power output of the signal generator minus the attenuation value of the attenuator is equal to the power output of the port under test. 5.2.2.2 High-level measurement
Insert a calibrated directional coupler between the port under test and the load. If necessary, connect a calibrated attenuator and a suitable filter (to eliminate spurious signals, harmonics or other unwanted carriers) to the measuring arm of the spacer coupler in front of the power meter. The reading obtained should be corrected to take into account the total insertion loss of the directional coupler and any attenuator used. 5.2.3 Measurement of Gain, Attenuation and Isolation Gain, attenuation and isolation may be measured using a suitable level meter by direct calibration or by the alternative methods described in 5.2.4 and 15.2.5.
Isolation is measured by applying a signal to one of the ports of interest and measuring the resulting signal level at a second port. The test shall be made with all other ports terminated at their nominal impedance. The level of any unwanted signal shall be negligible. 5.2.4 Measurement by RF Substitution Method
The typical measurement equipment configuration is shown in Figure 6. This figure refers to a special case where the loss as a function of frequency is measured using an amplitude modulated swept frequency signal generator and a load (with impedances that match the nominal impedance of the transmission line). The display device can be either an XY recorder or a two-line oscilloscope as shown by the dotted line in the figure. The sweep voltage is applied to the × amplifier of the display device. When an XY recorder is used, the sweep rate should be consistent with the movement rate of the recorder. The RF signal output at the output port of the signal generator is amplitude modulated with an audio signal (for example, 1kHz) and is swept within a specified frequency range. The output of the RF detector is the original low-frequency signal. This signal is separated, amplified and detected by a low-frequency amplifier-detector (without a digital amplifier, it is convenient to display the insertion loss changes of the human). The amplitude of the low frequency signal is related to the size of the RF signal at the input port of the RF detector and to the insertion loss. This low frequency signal is then fed to the Y amplifier of the recorder or to one of the Y inputs of the oscilloscope. An additional detector is used to monitor any changes in the input level of the radio frequency signal applied to the device under test. In addition, this detector can be used to automatically control the output level of the signal generator. The Y input of the oscilloscope is used to verify that the signal applied to the device under test remains constant. Note: An XY recorder can also be used to verify that the input level of the device under test remains constant by exciting the input of the amplifier detector to the output of the detector. Before making any measurement, the measuring equipment should be calibrated. The method is to connect the output coupler directly to the input detector, as shown in Figure 6, points A and B. The precision variable attenuator is adjusted to various values according to the requirements of the level calibration, such as: 0.1, 0.2 dB, 0.3 dB, 1.0 dB, 2.0 dB, etc. The frequency signal generator is adjusted to each fixed frequency point, and the precision variable attenuator is adjusted to establish the electrical calibration at these frequency points. The device under test is connected between points A and B in the test base equipment configuration diagram shown in Figure 6, and the attenuator is set to the minimum value of the calibration process. Then, the insertion loss of the device under test is plotted against the frequency. Assuming that the output coupler is replaced by an isolator, and that all the output power passes through the variable precision attenuator and detector, this method can be used to measure loss values up to 10 dB. 5.2.5 Measurement by intermediate frequency substitution method
Measure the gain, insertion loss or return loss (modulus and angle) using commercial measurement equipment based on swept frequency technology. This measuring equipment uses a mixer that is linear over a wide dynamic range (e.g. 70B) to convert both signals (input and output signals for measuring insertion loss and incident and reflected signals for measuring oscilloscope loss) into intermediate frequency signals (e.g. 20MHz) and measure them by substitution at the intermediate frequency. These mixers have a uniform response in the frequency range of 10MHz to 12GHz. This measuring equipment can determine absolute loss over a wide range with an accuracy of 0.1dB/10dB and can measure broadband frequency response within a 3dB range with an accuracy of 0.2dB. When using this type of equipment, the manufacturer's instructions should be strictly followed to obtain the highest accuracy. The results can be displayed by a meter, XY recorder or oscilloscope showing the relationship between gain (loss) and frequency. 5.3 Result attenuation method
The gain, loss or level at the specified frequency should be expressed in decibels or decibels relative to a given power as required. If the RF transmission line used in the survey is capable of transmitting multiple modes, the specific single mode or multiple modes to which the results apply shall be specified.
5.4 Details to be specified
When this measurement is required, the equipment specifications shall include the following: a. Voltage;
h. Gain and loss;
c. Frequency range;
d. Measurement method used (clauses 5.2.4 and 5.2.5). 6 Amplitude/frequency characteristics
6.1 Definition and general considerations
The amplitude/frequency characteristic is the relationship between the ratio of the output level to the reference voltage (expressed in decibels) and the frequency when the input signal level is kept constant. The reference level is the output level at the reference frequency (usually set as the center frequency of the frequency band). The frequency of the input signal differs from the frequency of the output signal by a fixed value,
This definition only applies to linear or approximately linear networks, and nonlinear networks are not included. 6.2 Measurement method
The swept frequency method is preferred for measurement. The point-by-point measurement method can also be used, but it is time-consuming, and the measured value may change between the selected frequency points, and these changes may not be detected. Both methods can use the above-mentioned RF or IF substitution technology. In the measurement, frequency converters can be used, provided that their inherent errors are tolerable. The protection measures are similar to those in Article 7.2.1. 6.3 Result Representation
When the swept frequency method is used for measurement, the measurement results shall be represented by a photograph of the display graph or a line drawn by an XY recorder. When the results are not represented by a graph, they shall be represented as follows: \The amplitude/frequency characteristic is within 6.0 to 6.1 GHz, and is within +0.2 to -0.1 dB relative to the amplitude at 6.2 GHz."13
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When the point-by-point measurement method is used, the measurement results can be tabulated or expressed in the above method. When the measured characteristics have obvious fluctuations, their peak-to-peak amplitudes (dB) and their corresponding frequency bands and 6.4 Details to be specified
When this measurement is required, the equipment specifications should include the following: allowable amplitude changes;
b. Frequency range;
c. Reference frequency.
7 Group delay/frequency characteristics
7.1 Definitions and general considerations
For linear networks, the transfer function can be written as: H(jw)= A(w)eBta
Where: A(α)---the amplitude/frequency characteristic of a linear network; B()--the phase/frequency characteristic of a linear network (if the output signal lags behind the input signal, it is considered to be a positive value). The group delay () of the network is defined as; the first-order derivative of B(a), that is: (α) = dB()
The unit is seconds.
Its definition is the same for IF and RF.
Usually, what needs to be measured is the group delay variation. This group delay variation is the difference between the above group delay and the reference frequency group delay. 7.2 Measurement method
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There are two measurement methods. The first method is to use a frequency modulated RF signal that sweeps within a specified frequency range. The first method is to use an amplitude modulated RF signal that sweeps within a specified frequency range, but this method is not suitable for highly nonlinear networks. 7.2.1 Frequency modulation method
The frequency modulation method usually uses a frequency modulated RF signal that sweeps within a specified frequency range. The signal is usually obtained by frequency conversion from a similar IF signal. In fact, the measurement is performed at the IF. As described in Section 3 of Part 1 of this series of standards, "Measurements within the intermediate frequency range", Article 8. However, broadband linear up-converters and down-converters are required. The upconverter and downconverter should be connected to the RF device under test to match the frequency range of the IF signal generator and receiver. This requires two measurements, one to measure the device self-loop connection to determine its residual group delay, and another to insert the device under test to determine its total group delay. The residual group delay is then subtracted from the total group delay to obtain the group delay of the device under test. The impedance of the RF port of the upconverter and downconverter should be very close to their nominal values to minimize the group delay fluctuation when the converters are connected with long transmission lines. If this is not paid attention to, errors may occur because the effect of the equivalent transmission line length of the device under test is not taken into account in the initial calibration.
These converters should operate linearly between their IF and RF ports. In addition, the upconverter output RF port should be connected to an RF bandpass filter to ensure that only the upper sideband or the lower sideband is applied to the device under test. If the device under test itself has an RF bandpass filter, this filter can be omitted.
7.2.2 Amplitude Modulation Method
As shown in Figure 7, the amplitude modulation method uses an amplitude modulator (such as a PIN diode) to perform sinusoidal modulation on the output of the RF sweep signal generator at a frequency between 100kHz and 2MHz. Before this, the output level of the signal generator should remain constant. The signal is connected to the output end of the device under test! The broadband detector demodulates it and then adds it to the phase detector to compare its phase with the phase of the original modulated signal. The phase of the modulated signal at the output end of the broadband detector should be independent of the RF input level of the broadband detector. The output of the phase detector is proportional to the sample delay change.
7.3 Result Representation
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The group delay/frequency characteristic shall preferably be presented as an oscilloscope display curve with frequency as the horizontal axis. The presentation shall be similar to that of Figure 9 in Section 3 of Part 1 of this series of standards, "Measurements in the intermediate frequency range". When the results are not presented graphically, they shall be presented as follows: "Over the frequency range of 6.135 to 6.155 GHz, the total group delay variation is 1.5 ns". When there are significant fluctuations in the measured characteristic curves, their peak-to-peak amplitudes (in nanoseconds) and the corresponding frequency bands shall be indicated. If the group delay/frequency characteristic on either side of the carrier frequency can be represented accurately enough by a finite series of terms, it may be represented by the expansion of the series without displaying the characteristic curve. The coefficients of these terms may be calculated from the measured response characteristics and expressed in ns/MHz, ns/(MHz), ns/(MHz) as appropriate. 7.4 Details to be specified
When this measurement is required, the equipment specifications shall include the following: c. Required RF bandwidth;
Modulation (measurement) frequency;
The allowed group delay variation within the required RF bandwidth; c.
d. The measurement method used (7.2.1 or 7.2.2). 8 Multicarrier intermodulation ratio
8.1 Definition
When two or more signals of specified frequencies pass through a nonlinear network and produce a specified identical level at the output, the multicarrier intermodulation ratio of each intermodulation product is the ratio of the level of the product to the above specified identical output level, usually referred to as the intermodulation ratio. 8.2 Measurement method
The measurement equipment used is configured as shown in Figure 8. The RF signals output by calibrated signal generators (1) and (2) are added through a four-port connector H, and the resulting signal is applied to the input of the device under test. A directional coupler (1) with a known coupling degree can be used together with a power meter to check the level of the signal. The internal attenuators of the generators (1) and (2) cannot provide sufficient decoupling. In order to avoid the two signal generators affecting each other through the connector, an attenuator or isolator must be inserted between the output of the generators (1) and (2) and the input of the connector H. The device under test is loaded through a matching impedance. The directional coupler (2) samples part of the output signal and adds it to the end E of the connector H. The spectrum analyzer is connected to the output of the coupler (2) and the output of the reference signal generator through the connector H. Sometimes an isolator or attenuator needs to be inserted at the input of the spectrum analyzer. In order to avoid measurement errors, the spectrum analyzer should have an appropriate dynamic range and intermodulation ratio. The measurements are carried out at different frequencies throughout the relevant frequency band. The level of each signal added to the device under test is adjusted to obtain the specified output level, except when there is obvious gain compression (see Note ②). The reference signal generator is used to determine the frequencies of the intermodulation products displayed by the spectrum analyzer. If necessary, it can also be used to measure the levels of these intermodulation products.
Note: () If the gain of the device under test is not uniform within the specified frequency band, then the above test procedure requires different input signal levels. If the output levels of the various frequencies of the applied signal are not equal, the minimum level is taken as the reference level. (2) If the device under test exhibits significant gain compression, the level of each intermodulation product can be compared with the output level obtained by specifying the same input level.
8.3 Expression of results
The measurement results shall be expressed as the ratio of the level of each intermodulation product to the level of any test signal at the output of the device under test (expressed in decibels).
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These results shall be expressed by a photograph of the level of each test signal displayed on a spectrum analyser and/or by a graph of the relationship between the positive modulation ratio (decibel) of each individual modulation product and the test signal output level. 8.4 Details to be specified
When this measurement is required, the equipment technical requirements shall include the following: frequencies of simultaneous input test signals;
output levels or level ranges of these test signals; h.
intermodulation products to be measured;
maximum value of the intermodulation ratio allowed.
9 AM/PM conversion coefficient
9.1 Definition
The AM/PM conversion coefficient is defined as: the derivative of the phase shift of the output signal with respect to the input signal voltage when the input frequency is given. It is expressed in degrees/decibels.
9.2 Measurement method
AM/PM conversion can be measured by static method or dynamic method. 9.2.1 Static method
The measuring equipment is shown in Figure 9, where a suitable phase meter, such as a network analyzer or a voltmeter, is used to detect the phase change of the output signal caused by a specified input signal level change (e.g. 1.0 dB) of the device under test. Before making the measurement, the phase shift error caused by the level change of the measuring equipment itself (especially the test attenuator and phase meter) should be determined. In order to minimize the phase shift caused by the measuring equipment, a suitable attenuator should be used, such as a rotary precision attenuator. 9.2.2 Dynamic Method
The typical measuring equipment configuration is shown in Figure 10, which is basically a device for measuring differential gain distortion in the baseband. In order to be able to perform measurements in the RF band, frequency modulators and demodulators are required in conjunction with up-converters and down-converters. The residual AM/FM values of these devices should be small enough to be negligible compared to the measured values. Alternately insert and remove a test network with accurately known group delay/frequency characteristics from the input of the device under test, note the relative change △ in the amplitude of the demodulated test signal, and then the amplitude modulation/phase modulation conversion coefficient (K) can be calculated by the following equation)24()
Kp = (a)(2元f)2
Where: baseband test frequency;
t…—-order derivative of the group delay/frequency characteristics of the test network, where the angular frequency is expressed in rad/s; c-—angular frequency of the applied RF signal.
The test network usually has a parabolic group delay/frequency characteristic. In this case, and △ are both proportional to the frequency difference relative to the center frequency, then equation (7) can be simplified to: 4
Where: A△ is the slope of the curve that changes with frequency, %MHz; T2-parabolic group delay coefficient, ns/(MHz)\;——test frequency, MHz1
K. AM/PM conversion coefficient, )/dB
It should be noted that equation (8) is only applicable when (K) is a constant. The positive AM/PM conversion coefficient (K,) should be explained by:
1The symbol K is used in the IEC standard, and K is used in this standard to represent the AM/PM conversion coefficient. The latter is more common at home and abroad. 16
Amplitude modulation causes delayed phase modulation. GB11299.2--89
In summary, the error of the AM/PM conversion coefficient (K) is determined by the accuracy of the and, therefore, the determination of these quantities should be such that the error can be ignored. If the test frequency is too low, the sensitivity of the test equipment will be insufficient; conversely, if the frequency is too high, it will cause a large error. The maximum test frequency depends on the bandwidth of the device under test. Usually, the value of f is between 2.0 and 3.0 MHz. 9.3 Result expression
The measurement result is expressed in degrees/dB, preferably in the form of a graph showing the relationship between the AM/PM conversion coefficient and the input signal level for each given frequency.
9.4 Details to be specified
When this test is required, the equipment technical requirements should include the following: The measurement method used (see 9.2.1 or 9.2.2): a.
b. Level and frequency of the input RF signal; maximum value of the AM/PM conversion coefficient allowed. c.
10 Spurious signals (including harmonics)
10.1 Definition
10.1.1 Spurious signals
Spurious signals are unwanted signals other than intermodulation products. 10.1.2 Harmonics
Signals with frequencies n times the frequency of the wanted signal are called harmonics, where n is an integer. 10.2 Measurement methods
The measurement method depends on whether the spurious signal is in-band or out-of-band. 10.2.1 In-band spurious signals
A suitable measurement equipment configuration is shown in Figure 11, where a frequency-selective level meter can be used instead of a spectrum analyzer. If the output level of the device under test is low, for example, below 0 dBm, a suitable low-noise amplifier can be used to put the output at a level suitable for the spectrum analyzer, but it should be noted that the input signal level should not be so large as to produce obvious intermodulation products in the spectrum analyzer. The dynamic range of the spectrum analyzer should not be less than 70dB, and the influence of any inhomogeneity of the amplitude/frequency characteristics of the measurement equipment should be taken into account. In the case where the RF carrier may cause the spectrum analyzer to overload, the measurement equipment configuration shown in Figure 12 should be used: 10.2.2 Out-of-band spurious signals
The measurement equipment configuration shown in Figure 11 can also be used to measure out-of-band spurious signals. If the spectrum analyzer is overloaded, the equipment configuration method shown in Figure 12 should be used instead. The bandwidth of the bandpass filter should be smaller than the rated bandwidth of the device under test.
The bandpass filter is tuned to the specified output frequency and reflects the measured signal to the spectrum analyzer with negligible loss. Its accuracy is limited by the circulator characteristics and the filter reflection characteristics. When the out-of-band signal frequency is so high that multiple propagation modes exist in the RF feed line, the method of measuring harmonics in 10.2.3 should be used. Except for the method of connecting the circulator A port with a short circuit to calibrate the spectrum analyzer, 10.2.1 is fully applicable. It should be noted that after connecting the channel filter and the standard terminal load to the circulator A port, the carrier level displayed by the spectrum analyzer should be greatly reduced. For example, it is reduced by 303.
10.2.3 Harmonics
When measuring harmonics, the measurement equipment configuration shown in Figure 11 and the provisions of 10.2.1 can be used. In addition, at the harmonic frequency, the input impedance of the spectrum analyzer or frequency-selective level meter should be the same as the impedance of the device under test. If the output circuit of the device under test is waveguide, then one or more suitable wave-mode converters are required.
10.3 Presentation of results
GB 11299.2--89
The measurement results are preferably presented by a photograph of the display of a spectrum analyser with vertical and horizontal calibration scales, or by a record of an X-recorder.
If a frequency-selective level meter is used, its bandwidth should be indicated, and the frequency and level of the spurious signal should be indicated. 10.4 Details to be specified
When this measurement is required, the following should be included in the equipment specifications: a.
Level and frequency of the unmodulated carrier;
Frequency range of the spurious signal to be measured;
Maximum permissible spurious signal level;
Points where harmonic measurements are required.
Frequency measurement port
Band pass filter
, (set as required)
Baseband signal
Generator
Baseband RF
Oscillator
Attenuator or
Amplifier
Frequency converter
(set as required)
Inductor
Equipment configuration for measuring unmodulated RF carrier frequency Equipment under test
(see note)
Directional coupler
Filter and
Attenuator
Isolator
Coupler
Figure 2 Equipment configuration for measuring modulated RF carrier frequency Recorder
(set as required)
Analyzer
Note: The equipment under test can be a medium Frequency modulator/upconverter, or a directly modulated RF transmitter VSWR indicator RF signal generator (modulation) Low-pass filter Attenuator Measuring line with moving probe and detector Typical equipment configuration for point-by-point measurement of VSWR using measuring line Figure 3 Sweep-frequency signal generator (modulation) Automatic electronic control GB11299.289 Storage oscilloscope with scale Low-pass filter Combiner Automatic electronic control Detector Attenuator Frequency amplifier and detector Test line with moving probe and detector Typical equipment for measuring voltage standing wave ratio with frequency sweep of measuring line 4 Wavelet analyzer Sweep frequency signal Sweep frequency RF generator Isolator Automatic level control (set by power) Automatic level control (set by range) Sweep signal generator (amplitude) Sweep signal Detector Filter Incident power Input monitoring (set by frequency) Variable radiation Attenuator |Reflected power
Four-port fixed-pole coupler (reflectometer)
Short-circuit detector and
filter
replace the device under test
Figure 5 Typical equipment configuration for measuring return loss using a reflectometer DC or detected AM signal
Detector
Input directional
Coupler
Low-pass filter
Output directional
Coupler
Radio variable precision attenuator
Detector
Typical equipment configuration for measuring RF gain or lossY
Dong wave filter
(according to the band setting)
Recorder
Low-frequency logarithmic amplifier
and detector289
Storage oscilloscope with scale
Low-pass filter
Regulator
Automatic voltage control
Detector
Attenuator
Frequency amplifier
and detector
Measurement line with moving probe and detector
Typical equipment for measuring voltage standing wave ratio by frequency sweeping of measurement line
Wavelet
Swept frequency signal
Swept frequency RF
Generator
Isolator
Automatic level control
(Set by power)
Automatic level control
(Set by section)
Swept signal
Sensor (amplitude)
Lazy signal
Detector
Filter
Incident power||tt| |Input monitoring
(button setting)
Variable reflector
Attenuator
Reflected power
Four-port fixed-coupler
coupler (reflectometer)
Shorts
Detectors and
filters
Replace the device under test during calibration
Figure 5 Typical equipment configuration for measuring return loss with a reflectometer DC or detected AM signal
|Detector
Input directional
Coupler
Low-pass filter
Output directional
Coupler
Radio frequency variable precision
Precision attenuator
Detector
Typical equipment configuration for measuring RF gain or lossY
Dong wave filter
(according to the wing setting)
Recorder
Low-frequency logarithmic amplifier
Device and detector289
Storage oscilloscope with scale
Low-pass filter
Regulator
Automatic voltage control
Detector
Attenuator
Frequency amplifier
and detector
Measurement line with moving probe and detector
Typical equipment for measuring voltage standing wave ratio by frequency sweeping of measurement line
Wavelet
Swept frequency signal
Swept frequency RF
Generator
Isolator
Automatic level control
(Set by power)
Automatic level control
(Set by section)
Swept signal
Sensor (amplitude)
Lazy signal
Detector
Filter
Incident power||tt| |Input monitoring
(button setting)
Variable reflector
Attenuator
Reflected power
Four-port fixed-coupler
coupler (reflectometer)
Shorts
Detectors and
filters
Replace the device under test during calibration
Figure 5 Typical equipment configuration for measuring return loss with a reflectometer DC or detected AM signal
|Detector
Input directional
Coupler
Low-pass filter
Output directional
Coupler
Radio frequency variable precision
Precision attenuator
Detector
Typical equipment configuration for measuring RF gain or lossY
Dong wave filter
(according to the wing setting)
Recorder
Low-frequency logarithmic amplifier
Device and detector
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