GB/T 11299.3-1989 Satellite communication earth station radio equipment measurement methods Part 1: Measurements common to subsystems and subsystem combinations Section 3: Measurements in the intermediate 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 Three-Measurements in the i. 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". GB11299.389
IEC510-1-3(1980)
This standard is equivalent to the International Electrotechnical Commission standard IEC510.13 (1980) "Methods of measurement for radio equipment used in satellite earth stations for satellite communicationPart 1: Measurements common to sub-systemsand combinations of sub-systemsSection Three-Measurements in the i. f, range". 1 Subject content and scope of application
This standard specifies the basic measurement methods for eight electrical characteristics such as return loss and input and output levels in the i. f, range. The measurement methods given in this standard are applicable to frequency division multiplexing (FDM)/FDMA/FM systems. Measurement methods for other multiple access technologies and systems with other modulation methods are under consideration. 2 Definitions
For the purpose of this standard, the intermediate frequency band refers to the frequency range occupied by the modulated signal at the output of the frequency modulator or the input of the frequency demodulator. Note: The nominal center frequency of the intermediate frequency band is usually 70 MHz, but other frequencies may also be used. 3 Return loss
3.1 Relationship between impedance, return loss and reflection coefficient In satellite communication earth stations, the measurement of return loss is of concern rather than impedance or reflection coefficient. The return loss (L) of an impedance (Z) relative to its nominal value (Z) is given by: 12+2,
L = 20 logl
or by:
L= 20 log1o
where: ... impedance Z) relative to Z. Voltage reflection coefficient. That is: 2
z+z.
Note: Usually the nominal impedance (Z) of the intermediate frequency internal connection point is 75α pure resistance (unbalanced). 3.2 Measurement method
Return loss can be measured by point-by-point measurement method or by frequency sweeping method. No matter which method can guarantee the required accuracy (typically approved by the Ministry of Electronics Industry of the People's Republic of China on March 1, 1989, implemented on January 1, 1990, GB11299.3-89
±1dB), it can be used. The following is an example of the frequency sweeping method. In this example, the following equipment is required, see Figure 1. A frequency sweep generator (including a frequency standard signal generator); a measuring bridge; a receiver consisting of a frequency converter, a frequency selective amplifier with a graduated attenuator, and an amplitude detector; a DC power supply as a reference level; an oscilloscope; an electronic parallel switch. The frequency sweep method is used to measure the return loss of a linear passive end. For example, the return loss at the input end of a network is measured. This method can also be used to measure the return loss of a linear active device. For example, the return loss at the output end (source impedance) of the device is measured, but during the measurement, there should be no signal in the circuit, and the device under test can be regarded as a linear passive network. The return loss of cables, attenuators, adapters, etc. used during the measurement, as well as the return loss of the input and output ends of the measuring equipment, can also be checked using the same method. 3.3 General considerations for measuring equipment (see Figure 1) 3.3.1 Sweep frequency generator
The sweep frequency generator consists of a sweep oscillator, a master oscillator and an externally excited oscillator. The master oscillator sweeps at the intermediate frequency (f), and the frequency of the externally excited oscillator is the intermediate frequency plus the operating frequency (F) of the frequency-selective amplifier. The repetition frequency of the sweep (f.) can be selected in the range of 10100 Hz. The passband of the receiver part, that is, the passband of the frequency-selective amplifier, amplitude detector and oscilloscope, is about 50 to 100 times this sweep repetition frequency. The signal waveform of the sweep oscillator is preferably a triangular wave or a sine wave. 3.3.2 Measuring bridge
Within the specified signal level range, the voltage at the output of the bridge must be proportional to the magnitude of the reflection coefficient of the measured end. The bridge network shown in Figure 2 is such an example.
With standard A standard impedance of nominal value (e.g. 7.752) may be connected internally to the bridge or externally. An isolation transformer may be used to ground the measuring device, the device under test, or both. A hybrid circuit may also be used which has electrical performance equivalent to that of a bridge circuit and does not require a separate isolation transformer. 3.3.3 Frequency-selective amplifier
Since the reflected power is often of the same order of magnitude as the harmonic power of the measurement frequency, the harmonics of the measurement frequency may affect the accuracy of the measurement, so it is recommended to use a frequency-selective amplifier. 3.3.4 Receiver sensitivity
The minimum level that the receiver can detect shall be at least 20 cB lower than the minimum level expected when the bridge is under the conditions of 3.4.2. 3.4 Measurement procedure
The measurement procedure consists of three steps: calibration, checking the balance of the measuring bridge and measurement. 3.4.1 Calibration
Adjustment Adjust the output level of the master oscillator so that the required voltage is obtained across the impedance (Z) on the bridge. Be careful to avoid overloading the device under test.
Put the test arm of the bridge in an open or short circuit state, and adjust the attenuator at the input end of the frequency-selective amplifier so that an appropriate true current level is obtained at the output end of the amplitude detector.
Then, as shown in Figure 1, use the electronic switch on the front of the oscilloscope to compare the above DC level with the reference DC level. When the two traces on the oscilloscope coincide, the two DC levels are equal. Record the reading on the attenuator at this time. Note: For calibration, a standard mismatched terminal can be used, that is, an impedance with a known return loss (for example 20dB3) can be used instead of an open circuit or a short circuit. 3.4.2 Check the balance of the measuring bridge
Connect a standard 75Q impedance (2.) to the measuring end of the bridge to replace the unknown impedance (Z) . Adjust the graduated attenuator until the traces on the oscilloscope screen are close to overlapping to check the bridge balance. Only when the receiver has a high enough sensitivity can the traces be accurately overlapped. GB11299.3-89
Record the attenuator reading when the traces overlap or when the receiver sensitivity reaches the limit value. This reading determines the maximum return loss that can be measured within the specified accuracy range. Return losses 20dB less than the above value can be measured with a measurement accuracy of +1dB. For example, when the attenuator reading is 50dB, a return loss value within 30dB can be measured with a measurement accuracy within ±1d3. 3.4.3 Measurement of return loss
Connect the unknown impedance (B) to the bridge and adjust the attenuator to make the measurement trace and reference trace overlap on the oscilloscope screen within the frequency band specified by the frequency marker indication.
The difference between the reading of the attenuator and the reading obtained in 3.4.1 is the return loss of the impedance (Z). Note: If a standard mismatched terminal with known return loss is used during calibration, the return loss value of the measured impedance (7) is the sum of the known return loss and the difference between the two readings of the attenuator.
3.4.4 Measurement of return loss at the output of active devices The above measurement method is usually also used to measure the return loss of the output of the device under test. More suitable methods are under consideration.
3.5 Results presentation method
The measurement results are preferably presented by an oscilloscope display curve or photograph with vertical scale marks, as shown in Figure 3 (or inverted up or down). The reference line can also be displayed on the oscilloscope.
In any case, in addition to the measurement curve, the bridge balance calibration curve should also be displayed. When the measurement results are not presented graphically, they shall be presented as follows: \In the range of 60~80MHz, the return loss is better than 26dB; the bridge balance is better than 50dB". 3.6 Details to be specified
When this measurement is required, the equipment specifications shall include the following: return loss limit;
b, frequency band range.
4 Input and output levels
4.1 Definitions and general considerations
The input voltage is transmitted from a signal generator with a nominal output impedance (Z.) to a nominal output impedance (Z,) of the resistive load 1, and the input level is the level on the load (Z.). Correspondingly, the output voltage is the RMS value of the voltage between the two ends of the terminal load (Z,), and the output level is the level of the load (2). Note: When the input impedance or output impedance of the device under test is not a pure impedance impedance (Z.), the actual voltage or level measured is slightly different from the maximum value that can be obtained.
4.2 Measurement method
First, connect a signal generator to a dummy load, whose impedance is equal to the nominal impedance of the system under test. Then adjust the voltage trained on the dummy load to the specified value, that is, add the specified voltage to the system under test. Then connect the signal generator to the input end of the system under test, and at the same time, connect the nominal impedance load (Z) to the terminal of the system under test, and measure the output level of the system under test. Use a level meter calibrated with a sinusoidal input signal to measure the input level and output level of the system under test. The measurement should be performed at the nominal center frequency of the intermediate frequency. The input impedance of the measuring instrument must be the same as the nominal impedance of the circuit under test. For example, the return loss of the 752 input impedance can be checked by the method described in Article 3.4.3. If the accuracy is required to be ±0.3dB, the return loss of the measuring instrument should be better than 30dB. In order to avoid errors introduced by unwanted signals (such as harmonics), it is recommended to connect a low-pass filter or band-pass filter with a known insertion loss, or use a frequency-selective voltmeter or frequency-selective level meter for measurement. Another method is to use a power meter, such as a thermal power meter. At this time, even a lower return loss (such as 15dB) can obtain the same accuracy as a common voltmeter (such as ±0.3dB accuracy). 24
GB11299.389
The insertion loss of the cable used should be deducted, with a typical value of 0.1 to 0.2dB. 4.3 Expression of results
For sinusoidal input signals, input and output levels may be expressed in volts (rms) or in milliwatts; or they may be expressed as the fraction of voltage and power relative to their reference values. 1 mW is usually taken as the standard value. 4.4 Details to be specified
When this measurement is required, the equipment specifications shall include the following: a. Test signal level; b. Test signal frequency; c. Nominal impedance value.
5 Amplitude/frequency characteristics
5.1 Definitions and general considerations
The amplitude/frequency characteristic is a curve that expresses the difference (in decibels) between the output level and the reference level when the input level is constant and the frequency is the independent variable.
Note: The reference level is usually the output level at the nominal intermediate frequency. Measurements on linear equipment differ from those on equipment containing nonlinear devices. For example, when the equipment contains a limiter or an amplifier with automatic gain control (AGC), the amplitude/frequency characteristics of their first few stages will be compressed. Or the equipment contains a frequency selection network, it is impossible to distinguish between linear and nonlinear parts. For this case, more complete measurement techniques are under consideration.
5.2 Measurement method
Measurement can be performed using the point-by-point measurement method or the sweep frequency method. Figure 4 shows an example of the configuration of the swept frequency measurement equipment. 5.3 General considerations for measurement equipment
When using the swept frequency method, the repetition frequency of the swept frequency generator, the waveform of the swept signal, the passband of the detector and the oscilloscope must meet the requirements of Section 3.3.1.
It must be ensured that the measurement results are not affected by the test multiple harmonics. Before starting to measure the device under test, the output of the signal generator should be connected to the input of the detector to determine the inherent error of the measurement equipment. These measurement equipment include cables, attenuators and other auxiliary equipment. 5.4 Measurement procedure
Use the method in 1.2 or in accordance with the above principle, keep the input level unchanged, and determine the output voltage at different frequencies (7) within the passband of the equipment. Within the normal input level range specified for the equipment, the measurement can be repeated with several different input levels. This top measurement can also be extended to the frequencies on both sides of the passband. In this case, the level at the measurement frequency (f) will be significantly attenuated. [This must be done using a frequency-selective voltmeter or frequency-selective level meter to avoid errors caused by harmonics of the measurement frequency. Note: Measurements with limiters and amplifiers with automatic gain control require special measures. Appropriate measurement methods are under consideration. 5.5 Representation of results
5.5.1 Amplitude/frequency characteristics
The test results are preferably presented using the oscilloscope display curve or photograph shown in Figure 5. The horizontal and vertical scales of the display must be calibrated. When the measured results are not to be represented graphically, they should be represented as follows: The standard frequency is 70MHz. When the frequency range is from 60 to 80MHz, the unevenness of the amplitude/frequency characteristic is 0.2~+0.1dB3". That is, the difference between the maximum value of the curve on the ordinate of Figure 54t and the ordinate value of 70MHz does not exceed 0.1dB: and the difference between the ordinate final value of 70MHz and the minimum value of the ordinate line 130 does not exceed 0.2dB. 5.5.2 Fluctuation component
GB11299.3--89
When the measured characteristic line has obvious fluctuation components, the peak-to-peak value can be used and expressed in decibels. And the frequency of those fluctuations should be stated 5. 5.3 Power series components
If power series components are required, they can be approximated based on the power series of the characteristic curve near the carrier frequency. The values of the components are preferably expressed as coefficients, for example, 0.01dB/MHz, 0.005dB/(MHz).0.003(MHz)3, etc. Or they can be expressed as the total change in the scan passband, for example, within the specified passband (such as ±10MHz), the linear component ().3(13): the secondary component 0.1dB, the tertiary component 0.1dB. 5.6 Details to be specified
When this measurement is required, the equipment technical specifications should include the following: the allowable range of amplitude change;
frequency range;
reference frequency.
|6 Static Automatic Gain Control (AGC) Characteristics
6.1 Definition
The static automatic gain control characteristics of an amplifier are represented by a curve of output level as a function of input level. The input signal frequency is the nominal intermediate frequency, and the units of input and output levels are both decibel values relative to 1mW. 6.2 Measurement Method
According to the method in Section 4.2, measurements are performed at different input levels using a signal generator with a decibel scale relative to 1mW and a frequency-selective level meter, see Figure 6.
If necessary, measurements can also be performed at other frequencies within the intermediate frequency passband of the equipment. 6.3 Result Representation
The measurement results are preferably represented by the curve shown in Figure 7. When the measurement results are not represented by a curve, the following example should be used. Means: "When the input level varies within the range of +10 to +50dB of the nominal value, the relative variation between its output level and the corresponding output level of the nominal input level shall not exceed +0.5 to +1.5dB". 6.4 Details to be specified
When this measurement is required, the equipment specifications shall include the following: Nominal input level:
The range of input levels;
The allowable limit of output level variation.
7 Dynamic automatic gain control (AGC) characteristics
The measurement method is under consideration.
8 Group delay/frequency characteristics
8.1 Definitions and general considerations
For linear networks, the transfer function can be written as: H(jw) = A(w)·e iBia)
Where: A(w)
Amplitude/frequency characteristics of linear network;
-Phase/frequency characteristics of linear network (if the output signal lags behind the input signal, it is considered positive). The group delay (α) of the network is defined as the first-order derivative of B(α) with respect to, that is: dB(α)
t(α) =
Unit is second
GB11299.3--89
Usually, the change of the basic group delay is measured. The change of the group delay is the difference between the above group delay and the group delay at the reference frequency. The measurement on linear equipment is obviously different from the measurement on equipment containing nonlinear devices. When the equipment contains a limiter with an AM/FM conversion effect, it will cause "indirect" distortion. For example, the change of the amplitude/frequency characteristics before the limiter will lead to a significant change in the group delay.
In some cases, the frequency selection network is an integral part of the equipment, so it is impossible to distinguish between the linear and nonlinear parts. For this case, more complete measurement techniques are under consideration. 8.2 Measurement methods
There are two basic measurement methods, namely point-by-point measurement method and frequency sweep method. Figure 8 is an example of the measurement equipment configuration for the latter method. 8.2.1 General considerations for measurement equipment
The following conditions should be provided:
a. Appropriate selection of modulation index and modulation frequency (f.) to ensure that the corresponding spectrum occupies an appropriate bandwidth within which the amplitude/frequency characteristics and group delay characteristics of the network under test are close to a straight line. The parasitic amplitude modulation generated by the modulator should be negligible relative to the amplitude/phase modulation conversion effect and the transmission capacity of the system under test. The demodulator should be insensitive to parasitic amplitude modulation, so a frequency tracking demodulator is more suitable for this requirement. c. The phase detector should be insensitive to amplitude modulation synchronized with the scanning frequency and does not require a reference phase input signal. d. The modulator and demodulator shown in Figure 8 should be of high quality, especially they should have a constant group delay characteristic. When the above conditions are met, the output voltage (V) of the phase detector (Figure 8) has the following relationship with the group delay (w) of the network under test: Vkμt(w)
Where: k-constant, representing the slope of the phase detector, V/rad; u 2 yuan.
Note: (i) In Figure 8, the same phase detector can measure the phase difference (μz) in addition to the group delay change (t). If a test frequency of 0.277778MHz is used, the output voltage of the phase detector for a 1° phase difference will be the same as the output voltage for a 10ns group delay change. For. Other test frequencies that meet the above condition a can also be used, but in order to avoid the influence of excessive noise, very low frequencies (such as 10kHz) cannot be used. (2) In large-capacity systems (such as 1800 channels or more), the group delay characteristics may be significantly affected by nonlinear networks such as traveling wave tube amplifiers, limiters, inverters, etc., which are used for amplitude modulation/phase modulation conversion. Therefore, in this case, the characteristics of the circuits adjacent to the limiter of the device under test (excluding the limiter) should be determined by measurement.
8.2.2 Measurement procedure
In the preferred measurement method shown in Figure 8, a sweep signal with frequency f and a baseband test signal with frequency f (f>) are applied to the baseband input of an isolated modulator. In the modulator, the sweep signal is frequency modulated with a high modulation index and the baseband test signal with a low modulation index to produce a frequency modulated IF signal. This modulated IF signal is sent to the network under test and demodulated by a high quality demodulator that recovers the baseband test signal (f). Since the IF signal is swept over the entire IF bandwidth, the demodulated baseband test signal has amplitude and phase variations, and the output signal of the phase detector is proportional to the IF group delay. After measurement, the fluctuation component and/or power level component of the group delay/IF characteristic can be determined. NOTE: Methods for measuring group delay variations in nonlinear networks are under consideration. 8.3 Result Presentation
8.3.1 Group Delay/Frequency Characteristics
The group delay/frequency characteristics are best presented as a graph displayed by an oscilloscope with frequency as the horizontal axis, as shown in Figure 9. When the measurement results are not presented graphically, they should be presented as follows: \In the frequency band of 60~80MHz, the total group delay variation is 2.5ns". The modulation frequency f of the test oscillator and the corresponding modulation index should also be given. 8.3.2 Fluctuation Component
GB 11299.389
When the fluctuating components can be identified from the measured characteristic curve, their amplitude (peak-to-peak) should be expressed in nanoseconds to identify the frequency of those fluctuations.
8.3.3 Power Series Components
If a finite series (usually three terms) can fairly accurately represent the group delay/frequency characteristics around the carrier frequency, then the expanded terms of the power series can be used to represent the resulting characteristic curve. The second term of the series is usually called the "linear" component; the second term is called the "parabolic" component. The coefficients of these terms can be calculated from the resulting characteristic curve, usually in ns/MHz. , ns/(MHz), ns/(MHz), etc., 8.4 Details to be specified
When this measurement is required, the equipment technical conditions should include the following: a: Test signal frequency (f):
b. Intermediate frequency band;
c. Allowable range of group delay variation.
9 Differential gain and differential phase characteristics 1)
9.1-General considerations
In a satellite communication earth station with a small capacity (for example, no more than 432 channels), the intermediate frequency amplitude/frequency characteristics (see Article 5) and group delay/frequency characteristics (see Article 8) of the equipment under test are measured. ,) is sufficient to evaluate the baseband distortion of the device. Nonlinear distortions such as amplitude modulation/phase modulation conversion and other linear distortions can generally be ignored. However, in systems with larger capacity, these distortions will not be negligible, so in addition to measuring the sample delay/frequency characteristics, it is also necessary to measure the differential gain and differential phase. Note: When the carrier interval is smaller than the required width of the transmission baseband, systems below the above capacity must also measure the differential gain and differential phase. From the measured values of differential gain and differential phase, the five-tone noise of the device under test can be calculated. This is beneficial when the five-tone noise is low. Because the measured modulation White noise measurements are meaningless when the noise of the modulator/demodulator is higher than the noise of the device under test. Differential gain (IDG) and differential phase (DP) are defined in Part 1, Section 4 * Baseband Measurement of this series of standards: This basic definition involves the transmission of a high-frequency, small-amplitude test signal and a low-frequency, large-amplitude sweep signal simultaneously through the baseband portion of the device under test. This can be extended to the intermediate frequency portion using a measurement modulator and a measurement demodulator. See Part 2, Section 7 "Frequency Modulator" and Section 8 "Frequency Demodulator" of this series of standards. The measurement modulator and measurement demodulator can be considered "ideal" for practical measurements. This means that their differential gain and differential phase distortion are much smaller than those of the device under test. They are all included in the commercial "line analyzer" type of instrument. 9.2 Relationship between differential gain and differential phase and parameters of the device under test and test frequency In order to better evaluate the influence of various parameters of the device under test and their changes with frequency on the test results, it is necessary to understand the relationship between the differential gain and differential phase expressions and device parameters (such as: amplitude/frequency characteristic curve, group delay/frequency characteristic curve and amplitude/phase modulation conversion coefficient).
If the device under test includes a linear network with a transfer function related to frequency and a linear network with amplitude/phase modulation conversion behind it, the relevant relationships are given in Appendix A.
Based on these relationships, the differential gain and differential phase can be calculated. The measurement results of gain and differential phase and the choice of frequency can make correct conclusions. These conclusions can be summarized as follows:
9.2.1 The meaning of differential gain and differential phase characteristic curves For actual networks that show flat amplitude/frequency characteristics, the measurement of its differential phase only reveals the group delay characteristics of the linear network, while the measurement of the differential gain characteristic only evaluates the combined influence of the amplitude/phase modulation conversion of the nonlinear network and the sample delay slope characteristics of the linear network preceding it. It can be seen from the formula in Appendix A that the second term in the differential phase (DP) expression and the first term in the differential gain (I) expression contain the derivatives of the amplitude/frequency characteristic curve, which can be ignored in the case of flat characteristic curves. Instructions for use:
1) Article 9, Article 10 and Appendix A (reference) are IFC12F (Central Office) 99, IEC12E (Central Office) 69.28
9.2.2 Selection of test frequency
GB11299.3--89
In the instrument used for differential gain and differential phase measurement, the test signal frequency can be selected by switch to meet different requirements. It can be seen from the formula in Appendix A that the differential gain is proportional to the square of the measurement frequency, which requires a relatively high test frequency. Generally in the range of 1 to 12MHz to obtain sufficient sensitivity. However, when using a high test frequency, its average effect should be considered. The size of the differential phase is proportional to the test frequency, so a relatively low test frequency can be used, generally 100 to 500kHz has sufficient sensitivity. These lower test frequencies can make the display clearer. Due to these considerations, the results of differential gain and differential phase measurements are always expressed in relation to the test frequency used. 9.2.3 Scale of the test equipment
From Appendix A, it can be seen that DG/0.002/% and DP/0.The 36/% term is independent of the test frequency f㎡. For linear networks without AM/PM conversion (Kp--0), these quantities are curvature in nanoseconds squared and group delay in nanoseconds. In some cases, differential gain and differential phase measurement equipment can also be scaled in these units, i.e., the scaling is performed by changing the gain at the same time as the test frequency. Thus, for a given device under test, the displayed response will be independent of the test frequency, as long as the test frequency is low enough to avoid averaging effects between sidebands. When using very low test frequencies (up to about 500kHz), scaling in nanoseconds is a common approach for line analyzers, and the scale is not affected by the test frequency. However, when using test frequencies above about 500kHz, it is usually necessary to use differential position scaling in degrees or radians.
It is important to note that in either case, the parameter measured is differential phase (see Figure 10). For networks consisting of a linear network and a nonlinear network in series, the above values depend on the influence of both the linear network and the nonlinear network. 9.3 Measurement Method bzxz.net
A simplified equipment configuration for measuring intermediate frequency differential gain and differential phase is shown in Figure 10. The scanning signal and the test signal frequency modulate the measurement modulator, the device under test is excited by the measurement modulator, the output signal of the device under test is demodulated by the measurement demodulator, and the test signal component is separated by a bandpass filter tuned to the test signal frequency. The amplitude and phase modulation of the output test signal, which are only related to the distortion of the device under test, are detected by the envelope detector and the phase detector respectively and sent to the vertical deflection plate of the cathode ray tube to display the differential gain and differential phase. The horizontal deflection is generated by the demodulated scanning signal, which is fed by the measurement demodulator to a low-pass filter. Note: (1) Commercial measurement instruments, usually called "line analyzers", provide the equipment shown in the dashed box in Figure 10. Such measurement instruments usually include additional equipment for scaling the vertical and horizontal display axes (not shown in Figure 10). (2: When the switch position is for measuring differential phase, Figure 10 is essentially the same as the equipment configuration for measuring group delay in Chapter 8. However, in the equipment configuration given in Chapter 8, the horizontal deflection is first driven by the sweep signal of the signal generator. This method is not used in "line analyzers". This measurement cannot be made when the transmitting and receiving parts of the measuring instrument are placed at two stations respectively. 9.4 Representation of results
The measured values of differential gain and differential phase are preferably represented by a photograph displayed by a cathode ray tube or by a line recorded by an XY recorder with appropriate scales on both axes. If possible, the same photograph should be used to represent both characteristics. In addition, the difference between the characteristic limit values and the corresponding sweep range should be stated.
9.5 Details to be specified
When this measurement is required, the equipment technical conditions The following contents should be included: a.
Test signal frequency;
Sweep width (MHz peak-to-peak);
Allowable differential gain distortion (%);
d. Allowable differential phase distortion (expressed in degrees) or group delay distortion (ns), 10 Intermediate frequency carrier frequency
10.1 Definition
GB11299.3-89
For this standard, intermediate frequency carrier frequency refers to the intermediate frequency output by the modulator when there is no modulation. 10.2 Measurement method
Figure 11 is a general equipment configuration diagram for measuring intermediate frequency carrier frequency. Filters are only required when there are spurious signals. Before measurement, the equipment under test and the test equipment should have sufficient warm-up time to achieve thermal stability, and the energy dissipation device must be turned off.
Then, depending on the required accuracy, a counting frequency meter with an appropriate gate time is used to read the measured frequency value. The readings of each count of the frequency meter can be recorded using the printer shown in Figure 11. In practical applications, hundreds of counts are sufficient. However, the exact number depends on whether there is noise modulated on the carrier signal or superimposed on the carrier signal. Usually, repeatable results can be obtained based on a series of average statistical analysis at several measurement intervals. 10.3 Representation of results
The readings of the frequency meter can be recorded manually or automatically as a function of time. The counting time of the frequency meter and the accuracy of the reference clock must also be noted.
10.4 Details to be specified
When this measurement is required, the equipment technical specifications should include the following: a.||t t||Nominal value of intermediate frequency carrier frequency;
Permitted frequency deviation within a specified time interval. b.
Equipment under test
Electronic amplifier
Oscillator
Oscillator
Frequency sweep generator
V1(ZZ.
Attenuator
Sweep oscillator
Amplifier
Detector
DC power supply
Equipment configuration for measuring return loss
Return loss
Figure 2 Bridge network for measuring return loss
Frequency (MHz)
Reflection coefficient
Figure 3 Example of inter-wave loss displayed by oscilloscope
Note: 1) The input impedance of the instrument used to measure the output voltage (V) should be Zo. ②7. Usually 750.
Intermediate frequency signal ()
Oscillator
GB11299.3
Measured intermediate frequency
Amplifier
Sweep oscillator
Detector
Equipment configuration for measuring amplitude/frequency characteristics
Intermediate frequency signal
Generator
Frequency (MHz.)
Example of amplitude/frequency characteristics displayed on oscilloscopeMeasured intermediate frequency
Amplifier
Oscilloscope
Electricity meter
Or level meter
Equipment configuration for measuring static automatic gain control (AGC) characteristics() string
-5040 —30 —20 —100
Input voltage (dBm)
Figure 7 Legend of static automatic gain control (AGC) characteristic curve Baseband test
Signal generation
Modulator
Test signal
Generator
Scanning signal
Generator
Transmitting part
Equipment under test
Intermediate frequency under test
GB11299. 3—89
Demodulator
Sweep oscillator
Filter
Equipment configuration for measuring group delay
Group delay (ns)
Frequency (M!Iz)
Phase detector
Figure 9 Example of group delay/frequency characteristics displayed by an oscilloscopea
Modulator
Frequency device under test
Demodulator
|Receiving part
Filter
Filter
Detector
Phase detector
Dong wave filter
X wave filter
Simplified equipment configuration for measuring the differential gain (DG) and differential phase (DP) of the intermediate frequency equipment Measuring the frequency
Filter
(Set up as needed)
Counting type
Frequency meter
Figure 11 Measuring the intermediate frequency Equipment configuration printer for carrier frequency
(set as needed)
GB11299.3-89
Appendix A
Mathematical relationship in Article 9.2
(reference)
For cascaded linear networks (showing amplitude and group delay changes) and nonlinear networks (showing amplitude modulation/phase modulation conversion), the differential gain I; and the differential phase P are given by the following formula:
0. 002fm[r(w) - 24. 1Kpt'(o))DP(w) = 0. 36fmEt(w,) + 2. 78Kp'(w))Wu Zhong: DG(a)
Differential gain, %;
Differential phase, (°);
2 yuan, f. is the scanning carrier frequency deviating from the center frequency; test frequency, MHz;
curvature characteristic of linear network, ns\;
group delay characteristic of linear network, ns;
slope of group delay characteristic of linear network, ns/MHz; slope of amplitude characteristic of linear network, dB/MHz; amplitude modulation/phase modulation conversion coefficient of nonlinear network, (°)/dB. Note: () In the above formula, if the increase of amplitude causes the increase of phase lag of output signal (relative to the input signal), K is positive. ②The transfer function of linear network is given by the following formula: H(w,) = a(w,)em)
where: α(w) amplitude characteristic;
() phase characteristic.
By definition:
r(a)=
d?a(w)/d(w)?
t(w) dq()/d(w)
（A1)
These formulas are valid for sufficiently low test frequencies (which avoid the averaging effect between the two sidebands of the test signal) and for AM/PM conversion that is independent of the swept carrier frequency. It can be seen that the differential gain and differential phase are expressed as the product of two factors. The first factor is a parameter of the measurement device, namely the test frequency; the second factor is determined by the device under test and is the sum of two terms: the first term is generated by the frequency response of the linear network ("direct response"), and the second term is generated by the frequency response of the linear network and the AM/PM conversion of the nonlinear network ("indirect response"). Additional Notes:
This standard was drafted by Nanjing Radio Factory. Adoption Notes:
111EC: The standard symbol is K. This standard adopts K\, which is commonly used in China and is also used in other foreign standards.
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