This standard specifies the basic measurement methods for subsystems such as amplifiers or simulated radio-relay systems composed of subsystems. This standard applies to the measurement of the following parameters within the baseband range. - Input and output impedance (return loss); - Input and output impedance: - Baseband gain or loss, - Amplitude frequency characteristics, - Group delay frequency characteristics, - Non-linear amplitude distortion, - Differential gain and phase distortion. The measurement methods for parameters related to specific baseband signals, such as frequency division multiplexed telephone, television or sound program transmission, have been given in the relevant substandards of this series of standards GB 4958 "Measurement methods for equipment used in terrestrial radio-relay systems Part 3, Measurements of simulated systems". GB/T 4958.15-1992 Measurement methods for equipment used in terrestrial radio-relay systems Part 1: Measurements common to subsystems and simulated radio-relay systems Section 4: Measurements in the baseband range GB/T4958.15-1992 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T4958.15—1992
eqv IEC 487-1-4:1984
Methods of measurement for equipment usedinterrestrial radio-relay systemsPart 1:Measurements common to sub-systemsand simulated radio-relaysystemsSection 4.Measurements in the baseband range basebandIssued on October 6, 1992
Implemented on May 1, 1993
Issued by the State Administration of Technical Supervision
National Standard of the People's Republic of China
Methods of measurement for equipment used in terrestrial radio-relay systemsPart 1: Measurements common to sub-systems and simulated radio-relay systems
Section 4: Measurements in the basebandThis standard is part of the series of standards "Methods of measurement for equipment used in terrestrial radio-relay systems" GB/T4958.15-1992
This standard is equivalent to the international standard IEC487-1-4(1984) "Methods of measurement for equipment used in terrestrial radio-relay systemsPart 1: Measurements common to sub-systems and simulated radio-relay systemsSection 4: Measurements in the baseband". 1 Subject matter and scope of application
This standard specifies basic measurement methods for subsystems such as amplifiers or simulated radio-relay systems composed of subsystems.
This standard applies to the measurement of the following parameters within the baseband range. Input and output impedance (return loss);
- input and output levels,
- baseband gain or loss,
- amplitude frequency characteristics;
group delay frequency characteristics;
- nonlinear amplitude distortion;
- differential gain and phase distortion.
The measurement methods for parameters related to specific baseband signals, such as frequency division multiplexed telephone, television or sound program transmission, have been given in the relevant substandards of this series of standards GB4958 "Measurement methods for equipment used in terrestrial radio-relay systems Part 3: Measurement of simulated systems".
2 Reference standards
GB2789 Basic technical requirements for network interfaces of analog microwave relay communication systems GB4958.11 Measurement of black-and-white and color television transmission 3 Linear input and output characteristics
3.1 Return loss
Approved by the State Administration of Technical Supervision on October 6, 1992 and implemented on May 1, 1993
3.1.1 Definitions and general considerations
GB/T4958.15—1992
In radio relay systems, the main concern is the measurement of return loss rather than the measurement of impedance or reflection coefficient. The return loss L of impedance Z to its nominal value Z is given by the following formula: z+z
L=201g
Or by the following formula:
Where: p is the impedance Z to Z. The voltage reflection coefficient is: Z-Zo
z+z.
(3)
Note: According to GB2789, for a telephone system with a capacity of 601800 channels, the nominal impedance Zo of its baseband port is 75Q pure impedance (unbalanced). For a small capacity telephone system (such as less than 24 channels), the nominal impedance Zo of its baseband port is 150Q pure impedance (balanced). 3.1.2 Measurement method
The return loss can be measured directly, or it can be calculated from the measurement of the complex impedance Z or the reflection coefficient P. It is advisable to directly measure the return loss using the bridge method described below. However, this is not the only method. Any method that can provide the required measurement accuracy (about ±1dB) can be used. Figure 1 shows the point-by-point measurement method. If there is a ground terminal in the device under test and the frequency-selective level meter, then both ends of the baseband signal generator must be isolated from the ground. When the frequency is above 1kHz, isolation can be achieved by using a transformer. In most cases, the transformer can be installed in the impedance measurement bridge or in the baseband signal generator. When the frequency is below 1kHz, the complex impedance is usually measured and the return loss is calculated from the results. Figure 2 shows the swept frequency measurement method. When measuring at baseband frequencies, a complete measurement setup consisting of a baseband swept frequency signal generator, a swept frequency control frequency selection level meter and an impedance measurement bridge (the bridge is the same as that used in the point-by-point measurement method) is usually used. Note: In order not to affect the measurement accuracy, the sweep speed should be much lower than the response time of the measurement setup and the device under test. The return loss of the cables, attenuators, adapters, etc. used in the measurement, as well as the return loss of the input and output connectors of the impedance measurement bridge, can also be measured using the following method. The test procedure consists of three steps: calibration, checking the balance of the measurement bridge and measurement. They are described below. 3.1.2.1 Calibration
Refer to Figures 1 and 2, with short circuit S. Connect the device instead of the one under test, and the return loss is 0dB. Note the reading of the frequency-selective level meter (Figure 1) or draw a calibration line on the oscilloscope screen (Figure 2). Note: During calibration, a standard mismatched terminal load Z1, i.e. an impedance with a known return loss (e.g. 20dB), can also be used instead of the short circuit. 2
GB/T4958.15—1992
Figure 1 Block diagram of return loss measurement by point-by-point method
1 Standard mismatched terminal load Z1, 2-short circuit Se, 3 Equipment under test, 4-standard impedance Zs, 5 Baseband signal generator: 6-measurement bridge: 7-frequency-selective level meter; 8-nominal impedance Zo
Block diagram of return loss measurement by sweep frequency method
1-standard mismatched terminal load Z1, 2-short circuit Se; 3 Equipment under test; 4-standard impedance Zs; 5-baseband sweep frequency signal generator; 6-measurement bridge, 7-sweep frequency-controlled frequency-selective level meter, 8-nominal impedance Zo; 9-oscilloscope
3.1.2.2 Check the balance of the measurement bridge
Use a terminal load with a nominal impedance of Z. to replace the equipment under test and connect it to the impedance measurement bridge. Adjust the input attenuator of the frequency-selective level meter so that its reading is equal to that during calibration, or so that the point on the oscilloscope trace that represents the worst return loss within the frequency sweep range coincides with the calibration line. The difference between the attenuator reading when using a short circuit and the attenuator reading when using a standard impedance is the return loss of the measuring device itself. If this return loss is X (dB), then the measuring device is suitable for measuring occasions where the maximum return loss is X-20dB, and the measurement accuracy is ±1dB. This calibration includes both bridge balance, leakage in the bridge, and the effects of any mismatch between the two nominal impedances Z. Note: The measuring device is very insensitive to the same error between the two impedances. This is because it measures whether the two impedances are equal, which is completely different from whether the two impedances have a specified value, such as 75Ω pure resistance. 3.1.2.3 Measurement
Connect the device under test, as shown in Figure 1 or Figure 2. 3
GB/T4958.15—1992
In the point-by-point measurement method (Figure 1), adjust the input attenuator of the frequency-selective level meter until its reading is the same as when the short circuit is connected. The difference between the attenuator value when the short circuit is connected and the attenuator value when the device under test is connected is the return loss of the device under test. In the swept frequency measurement method (Figure 2), adjust the attenuator so that the point on the oscilloscope trace line representing the worst return loss within the swept frequency range coincides with the calibration line. Then, the difference between the attenuator value when the short circuit is connected and the attenuator value when the device under test is connected is the return loss of the worst point of the device under test. Note: If a standard mismatched terminal load with a known return loss is used during calibration, the return loss of the device under test is the sum of the known return loss value and the difference between the attenuator value when the standard mismatched terminal load is connected and the attenuator value when the device under test is connected. 3.1.3 Presentation of measurement results
The results of the swept frequency measurement method shall preferably be presented as a photograph of an oscilloscope display with appropriate calibration marks. They may also be presented as a curve of an XY plotter or a hand-drawn curve. However, in all cases, a bridge calibration curve shall be provided as well as the measurement curve. When the measurement results are not presented in a graphical form, they shall be given as follows: "In the frequency range of 30kHz to 12MHz, the return loss is not less than 30dB and the bridge balance is not less than 45dB." The measurement results of the point-by-point measurement method shall still be presented as above, except that the measurement frequency interval (for example: 10 measurements per decade of frequency) is given in addition. They may also be presented as a graph with clear indication of the measured values. 3.1.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. Nominal impedance Zos
b. Frequency band range;
c. Permissible return loss limit.
3.2 Input Level
3.2.1 Definitions and General Considerations
In order to ensure that the signal generator is adjusted to the specified level when connected to the input of the device under test, it is necessary to define the input level of the device.
For television systems, the input level is defined as the peak-to-peak voltage across a terminal load with an impedance equal to the nominal value Z. For frequency-division multiplexed telephone systems, the input level is defined as the effective value voltage across a terminal load with an impedance equal to the nominal value Z. (or the power delivered to the terminal load). Note: If the input impedance of the device under test is different from Z., then the voltage at its input may be different from the input voltage defined above. 3.2.2 Measurement Methods
If the input test signal level is established as above, the output of the signal generator does not need to be adjusted when it is applied to the input of the device under test. The input level is measured using a broadband level meter, a frequency-selective level meter or a calibrated oscilloscope. The return loss of the terminating load shall be better than 30 dB for the nominal impedance Zo. NOTE: The above measurement steps are not required when using a meter calibrated in decibels with the electromotive force or potential difference across the matched load as the reference level. 3.2.3 Presentation of measurement results
It is not usually necessary to present the measurement result of the input level separately, as this level is generally part of some other measurement. 3.2.4 Details to be specified
The following items shall be specified in the detailed equipment specification: a. Nominal input impedance Zo
b. Standard input level and tolerance,
c. Waveform to be used.
3.3 Output level
3.3.1 Definition
The output level of the equipment is defined as the peak-to-peak voltage, rms voltage or the corresponding power delivered across a standard impedance terminating load with a nominal value of Z. Peak-to-peak voltage is usually only used in television measurements. 3.3.2 Measurement method
GB/T4958.15—1992
The output of the equipment under test is connected to a standard impedance terminal load. The measurement of the output level is the same as the measurement of the input level (see Section 3.2.2).
3.3.3 Table elements of measurement results
For television systems, the measurement results should be expressed in peak-to-peak voltage. For telephone systems, they should be expressed in decibels based on 1 mW.
3.3.4 Details to be specified
The following items should be specified in the detailed equipment specification: a. Nominal output impedance Zo;
b. Nominal output level and tolerance.
4 Linear transfer characteristics
The measurements described in this chapter are only for baseband transfer characteristics, which are largely independent of baseband signal levels within the normal range. Transfer characteristics related to baseband signal levels are given in Chapter 5. 4.1 Baseband gain or loss
4.1.1 Definition
Baseband gain is the ratio of the output level to the input level expressed in decibels. If the decibel number of the baseband gain is a negative value, then its sign is usually changed and this value is called loss. 4.1.2 Measurement method
In order to calculate the baseband gain, its input level and output level are usually measured. The measurement is as follows: For telephone systems, a test signal of a specified level is used. For television systems, a test signal of 1Vpp is used. The baseband gain is measured at a specific frequency, at which the deviation measured with and without pre-emphasis should be equal. For television systems, the gain can be measured with a non-sinusoidal waveform, such as the test signal shown in Figure 7 or Figure 13 in GB4958.11 "Measurement of black-and-white and color television transmissions".
4.1.3 Expression of measurement results
The baseband gain shall be expressed in decibels and its test frequency shall be indicated. 4.1.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. The frequency or waveform applied;
b. The required baseband gain and tolerance.
4.2 Amplitude-frequency characteristics
4.2.1 Definition
The amplitude-frequency characteristics are curves that take the baseband frequency as the independent variable, the input level as a constant, and the ratio of the output level to the reference level expressed in decibels. The input level should be much lower than the saturation level, and the reference level is the output level at a specific frequency. 4.2.2 Measurement methodbzxZ.net
The amplitude-frequency characteristics can be measured by the point-by-point method or the swept frequency method. For convenience, the point-by-point method is often used for measurements below 20kHz, and the swept frequency method is used for measurements at higher frequencies. In point-by-point measurement, a frequency-selective level meter should be used first, but a wideband level meter can also be used. When a wideband level meter is used, it must be verified that the harmonic power at the output of the baseband signal generator is 40B lower than the fundamental power, and the input of the level meter used should have a precision attenuator.
Figure 3 shows a typical block diagram for measuring baseband amplitude-frequency characteristics using the point-by-point method, which can also be used to measure gain or loss. Before measurement, place attenuator No. 1 at a value slightly larger than the gain of the device under test, then alternately place switch S in positions A and B, and adjust attenuator No. 2 so that the level meter readings at the two positions are the same. The gain or attenuation of the device under test can be obtained from the readings of the two attenuators. Although this measurement block diagram is mainly used for point-by-point measurement, it is also suitable for swept frequency measurement. In swept frequency measurement, a baseband swept frequency signal generator and a swept frequency-controlled frequency-selective level meter equipped with a cathode ray tube are used. Note: If the equipment under test contains a baseband level adjuster (baseband automatic gain control amplifier) ​​that works on an in-band pilot tone, the adjuster should be turned off or short-circuited.
Block diagram for amplitude-frequency characteristic measurement
1—Equipment under test 2—#1 attenuator, 3—#2 attenuator, 4—Baseband signal generator 5—Frequency selection level meter 4.2.3 Representation of measurement results
When performing sweep frequency measurement, a photograph of the oscilloscope display should be provided. If no graphical representation is used, the following example should be given: "Amplitude-frequency characteristic: +0.2~-0.1dB in the range of 300Hz~8MHz, reference frequency is 1MHz". Point-by-point measurements can be presented in a curve, list or the above form. 4.2.4 Details to be specified
In the detailed equipment specification, the following items should be specified if necessary: ​​reference frequency (e.g.: 100kHz);
b. Frequency band range;
Permissible amplitude deviation limit.
4.3 Group Delay Frequency Characteristics
4.3.1 Definitions and General Considerations
The transfer function of a linear network can be written as: H(jo)=A(0).eB(o)
where: A(の) represents the amplitude frequency characteristic and B(の) represents the phase frequency characteristic (positive if the phase of the output signal lags behind the phase of the input signal).
The group delay () of the network is defined as the first derivative of B(@), i.e.: dB(@)
The group delay deviation, i.e. the group delay frequency characteristic, is defined as the difference between the above group delay and the group delay at a reference frequency. Note: It is not necessary to measure the baseband group delay for every model of equipment (e.g. equipment used only for frequency division multiplexed telephone transmission). 4.3.2 Measurement method
A test signal that is slowly scanned from the lower frequency limit of 200kHz to the upper frequency limit of 10MHz at a rate of, for example, 50 times per second is amplitude modulated or phase modulated with a signal of an appropriate measurement frequency f. (for example, 20kHz). The composite signal mainly consists of a carrier frequency and two sidebands.
GB/T4958.15—1992
The signal is added to the test receiver through the device under test. Since there is a local oscillator in the test receiver that is swept synchronously with the test signal, a constant intermediate frequency signal is generated. This intermediate frequency signal is de-amplified or phase demodulated to restore it to the measurement signal ft. The measurement signal is then phase-detected to obtain a signal with a scanning rate. This signal is displayed on the oscilloscope, which represents the group delay value with the independent variable being the baseband frequency.
This measurement can be performed using a dedicated tester. In the case of amplitude modulation, the de-amplitude modulator in the baseband test receiver can be used to restore the input signal ft. 4.3.3 Presentation of measurement results
The measurement results shall be presented by means of a photograph of the oscilloscope display with necessary scale markings. When no graphical presentation is required, they shall be given as follows: "Total group delay variation: 87 ns in the range 200 kHz to 8 MHz." 4.3.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. Baseband frequency range;
b. Permissible group delay deviation.
5 Non-linear transfer characteristics
The non-linear transfer characteristics depend on the level of the baseband signal. This characteristic causes the sinusoidal test signal to produce harmonics. When the test signal is at more than two, intermodulation products will be generated.
5.1 Differential gain (non-linearity)
5.1.1 Definition and general considerations
Differential gain (non-linearity) is the incremental deviation measured by a small-amplitude high-frequency sinusoidal signal (test signal) transmitted in the same channel with the instantaneous value of a large-amplitude low-frequency signal (sweep signal) as the independent variable. For television systems, see Article 6.4 of GB4958.11. The differential gain (non-linearity) is defined as a function of the instantaneous value mentioned above, given by the following formula: DG(X)=
Where: DG(X) - differential gain,
X - instantaneous value of the input sweep signal;
A(X) - amplitude A of the output test signal with X as the independent variable.
A(X) - amplitude A of the output test signal when the sweep signal is zero. (6)
For an ideal device under test without distortion, the differential The gain (non-linearity) is zero. But for an actual device, the above function will appear to be variable. The actual device has the characteristic of differential gain (non-linearity) distortion (DG). DG is the difference between the limit values ​​of equation (6), usually expressed as a percentage as follows:
Amx=Aa×100%
The description of the relationship between differential gain and non-linearity and the selection of test signal frequency are given in Section 5.1.2. 5.1.2 Measurement method
A typical block diagram for measuring differential gain (non-linearity) is shown in Figure 4. It also includes the parts necessary for measuring differential phase. When measuring differential gain (non-linearity), the switch should be placed on the side where the amplitude modulation detector is selected. The baseband signal added to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a sweep signal. At the baseband output of the device under test, The test signal component is extracted and applied to the envelope detector. The envelope detector output, which is proportional to the amplitude of the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the sweep signal, or, if the device under test contains an IF and RF part, it can also come from the demodulation part of the IF signal. The sweep signal is a low-frequency signal, and its amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristics at any moment, the amplitude of the test signal should be much smaller than the amplitude of the sweep signal. The choice of test signal frequency depends on the part of the device under test to be examined, and it is usually much higher than the frequency of the sweep signal. When only the nonlinearity of the baseband part of the modulator and demodulator is examined, a relatively low frequency test signal is selected. If a test signal (e.g. between 50 and 500 kHz) is used, the measured value is called nonlinearity. When both the baseband part and the carrier part are to be examined, a test signal with a relatively high frequency
(e.g. within the range of 1 to 5 MHz) should be selected, and the measured value is called differential gain. Figure 4 Block diagram of differential gain (nonlinearity) and differential phase distortion measurement
1 - test signal generator, 2 - sweep signal generator, 3 device under test: 4 - bandpass filter; 5 - oscilloscope; 6 - amplitude modulation detector, 7 - phase modulation detector 5.1.3 Representation of measurement results
Differential gain (nonlinearity) distortion should preferably be represented by a photograph of the oscilloscope display, and the two axes should be appropriately calibrated; the horizontal axis should be calibrated with the sweep voltage, and if the device under test contains a modulator or demodulator, it should be calibrated with the frequency deviation. In addition, the distortion expressed as a percentage between the characteristic limit values ​​can also be given together with the sweep range expressed in megahertz. 5.1.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a.
Test signal frequency;
Sweep signal frequency,
Sweep amplitude expressed as peak-to-peak voltage or sweep width expressed as peak-to-peak frequency (MHz); c.
Maximum differential gain (non-linear) distortion allowed, expressed as a percentage. 5.2 Differential phase (group delay)
5.2.1 Definition and general considerations
Differential phase is the phase deviation measured by a small amplitude high frequency sinusoidal signal (test signal) transmitted in the same channel as a large amplitude low frequency signal (sweep signal) with the instantaneous value as the independent variable. For television systems, see GB4958.11, clause 6.5. Differential phase can be defined as a function of the instantaneous value above, given by the following equation: DP(X) = d(X)— in.
where: DP(x) is the differential phase;
is the instantaneous value of the input sweep signal,
d(X) is the phase of the output test signal with X as the independent variable; do
is the phase of the output test signal when the sweep signal is zero. (8)
For two ideal devices under test without distortion, the differential phase is zero. But for a real device, the above function will show a variation. Real devices have the characteristics of differential phase distortion (DP). DP is the difference between the limit values ​​of the above functions, usually expressed in (8
units, as follows:
GB/T4958.15—1992
DP-max -min () ....
Note: When a relatively low frequency (such as a few hundred kilohertz) test signal is used to measure the differential phase, the measurement also represents the change in the group delay of the intermediate frequency and radiation part of the device under test. In this case, the measurement equipment used is usually calibrated with group delay in nanoseconds (ns). The group delay and differential phase are proportional to the ratio of the test signal frequency. When a relatively high frequency (such as a few megahertz) test signal is used, the differential phase scale is mainly expressed in degrees.
5.2.2 Measurement method
The typical block diagram for measuring differential phase is shown in Figure 4, which also includes the parts necessary for measuring differential gain (nonlinearity). When measuring differential phase, the switch should be placed on the side where the phase modulation detection port is selected. The baseband signal applied to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a slowly varying swept frequency signal. At the baseband input of the device under test, the test signal component is extracted and applied to a phase detector. The phase detector output, which is proportional to the phase change of the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the swept signal or, if the device under test contains an IF or RF section, from the demodulated portion of the IF signal. The swept signal is a low frequency signal whose amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristic at any instant, the amplitude of the test signal should be much smaller than the amplitude of the swept signal. 5.2.3 Representation of measurement results
Differential phase distortion should preferably be represented by a photograph of the oscilloscope display. The two axes should be appropriately scaled: the horizontal axis should be scaled with the swept voltage and, if the device under test contains a modulator or demodulator, with the frequency deviation. In addition, the distortion expressed in degrees between the characteristic limits may also be given together with the sweep range expressed in volts or megahertz. 5.2.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. Test signal frequency,
Sweep signal frequency:
Sweep amplitude expressed in peak-to-peak voltage or sweep width expressed in peak frequency deviation (MHz); d.
Maximum allowable differential phase distortion, expressed in degrees. Additional notes:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 9
The maximum differential phase distortion allowed, expressed in degrees. Additional remarks:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 9
The maximum differential phase distortion allowed, expressed in degrees. Additional remarks:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 9
The maximum differential phase distortion allowed, expressed in degrees. Additional remarks:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 9
The maximum differential phase distortion allowed, expressed in degrees. Additional remarks:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 9
The maximum differential phase distortion allowed, expressed in degrees. Additional remarks:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 9
The maximum differential phase distortion allowed, expressed in degrees. Additional remarks:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 93. Presentation of measurement results
The measurement results shall be presented by means of a photograph of the oscilloscope display with necessary scale markings. When no graphical presentation is required, the following example shall be given: "Total group delay variation: 87ns in the range 200kHz to 8MHz." 4.3.4. Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. Baseband frequency range;
b. Permissible group delay deviation.
5. Non-linear transfer characteristics
The non-linear transfer characteristics depend on the level of the baseband signal. This characteristic causes the sinusoidal test signal to produce harmonics. When the test signal is at more than two, intermodulation products will be generated.
5.1 Differential gain (non-linearity)
5.1.1 Definition and general considerations
Differential gain (non-linearity) is the incremental deviation measured by a small-amplitude high-frequency sinusoidal signal (test signal) transmitted in the same channel with the instantaneous value of a large-amplitude low-frequency signal (sweep signal) as the independent variable. For television systems, see Article 6.4 of GB4958.11. The differential gain (non-linearity) is defined as a function of the instantaneous value mentioned above, given by the following formula: DG(X)=
Where: DG(X) - differential gain,
X - instantaneous value of the input sweep signal;
A(X) - amplitude A of the output test signal with X as the independent variable.
A(X) - amplitude A of the output test signal when the sweep signal is zero. (6)
For an ideal device under test without distortion, the differential The gain (non-linearity) is zero. But for an actual device, the above function will appear to be variable. The actual device has the characteristic of differential gain (non-linearity) distortion (DG). DG is the difference between the limit values ​​of equation (6), usually expressed as a percentage as follows:
Amx=Aa×100%
The description of the relationship between differential gain and non-linearity and the selection of test signal frequency are given in Section 5.1.2. 5.1.2 Measurement method
A typical block diagram for measuring differential gain (non-linearity) is shown in Figure 4. It also includes the parts necessary for measuring differential phase. When measuring differential gain (non-linearity), the switch should be placed on the side where the amplitude modulation detector is selected. The baseband signal added to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a sweep signal. At the baseband output of the device under test, The test signal component is extracted and applied to the envelope detector. The envelope detector output, which is proportional to the amplitude of the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the sweep signal, or, if the device under test contains an IF and RF part, it can also come from the demodulation part of the IF signal. The sweep signal is a low-frequency signal, and its amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristics at any moment, the amplitude of the test signal should be much smaller than the amplitude of the sweep signal. The choice of test signal frequency depends on the part of the device under test to be examined, and it is usually much higher than the frequency of the sweep signal. When only the nonlinearity of the baseband part of the modulator and demodulator is examined, a relatively low frequency test signal is selected. If a test signal (e.g. between 50 and 500 kHz) is used, the measured value is called nonlinearity. When both the baseband part and the carrier part are to be examined, a test signal with a relatively high frequency
(e.g. within the range of 1 to 5 MHz) should be selected, and the measured value is called differential gain. Figure 4 Block diagram of differential gain (nonlinearity) and differential phase distortion measurement
1 - test signal generator, 2 - sweep signal generator, 3 device under test: 4 - bandpass filter; 5 - oscilloscope; 6 - amplitude modulation detector, 7 - phase modulation detector 5.1.3 Representation of measurement results
Differential gain (nonlinearity) distortion should preferably be represented by a photograph of the oscilloscope display, and the two axes should be appropriately calibrated; the horizontal axis should be calibrated with the sweep voltage, and if the device under test contains a modulator or demodulator, it should be calibrated with the frequency deviation. In addition, the distortion expressed as a percentage between the characteristic limit values ​​can also be given together with the sweep range expressed in megahertz. 5.1.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a.
Test signal frequency;
Sweep signal frequency,
Sweep amplitude expressed as peak-to-peak voltage or sweep width expressed as peak-to-peak frequency (MHz); c.
Maximum differential gain (non-linear) distortion allowed, expressed as a percentage. 5.2 Differential phase (group delay)
5.2.1 Definition and general considerations
Differential phase is the phase deviation measured by a small amplitude high frequency sinusoidal signal (test signal) transmitted in the same channel as a large amplitude low frequency signal (sweep signal) with the instantaneous value as the independent variable. For television systems, see GB4958.11, clause 6.5. Differential phase can be defined as a function of the instantaneous value above, given by the following equation: DP(X) = d(X)— in.
where: DP(x) is the differential phase;
is the instantaneous value of the input sweep signal,
d(X) is the phase of the output test signal with X as the independent variable; do
is the phase of the output test signal when the sweep signal is zero. (8)
For two ideal devices under test without distortion, the differential phase is zero. But for a real device, the above function will show a variation. Real devices have the characteristics of differential phase distortion (DP). DP is the difference between the limit values ​​of the above functions, usually expressed in (8
units, as follows:
GB/T4958.15—1992
DP-max -min () ....
Note: When a relatively low frequency (such as a few hundred kilohertz) test signal is used to measure the differential phase, the measurement also represents the change in the group delay of the intermediate frequency and radiation part of the device under test. In this case, the measurement equipment used is usually calibrated with group delay in nanoseconds (ns). The group delay and differential phase are proportional to the ratio of the test signal frequency. When a relatively high frequency (such as a few megahertz) test signal is used, the differential phase scale is mainly expressed in degrees.
5.2.2 Measurement method
The typical block diagram for measuring differential phase is shown in Figure 4, which also includes the parts necessary for measuring differential gain (nonlinearity). When measuring differential phase, the switch should be placed on the side where the phase modulation detection port is selected. The baseband signal applied to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a slowly varying swept frequency signal. At the baseband input of the device under test, the test signal component is extracted and applied to a phase detector. The phase detector output, which is proportional to the phase change of the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the swept signal or, if the device under test contains an IF or RF section, from the demodulated portion of the IF signal. The swept signal is a low frequency signal whose amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristic at any instant, the amplitude of the test signal should be much smaller than the amplitude of the swept signal. 5.2.3 Representation of measurement results
Differential phase distortion should preferably be represented by a photograph of the oscilloscope display. The two axes should be appropriately scaled: the horizontal axis should be scaled with the swept voltage and, if the device under test contains a modulator or demodulator, with the frequency deviation. In addition, the distortion expressed in degrees between the characteristic limits may also be given together with the sweep range expressed in volts or megahertz. 5.2.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. Test signal frequency,
Sweep signal frequency:
Sweep amplitude expressed in peak-to-peak voltage or sweep width expressed in peak frequency deviation (MHz); d.
Maximum allowable differential phase distortion, expressed in degrees. Additional notes:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 93. Presentation of measurement results
The measurement results shall be presented by means of a photograph of the oscilloscope display with necessary scale markings. When no graphical presentation is required, the following example shall be given: "Total group delay variation: 87ns in the range 200kHz to 8MHz." 4.3.4. Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. Baseband frequency range;
b. Permissible group delay deviation.
5. Non-linear transfer characteristics
The non-linear transfer characteristics depend on the level of the baseband signal. This characteristic causes the sinusoidal test signal to produce harmonics. When the test signal is at more than two, intermodulation products will be generated.
5.1 Differential gain (non-linearity)
5.1.1 Definition and general considerations
Differential gain (non-linearity) is the incremental deviation measured by a small-amplitude high-frequency sinusoidal signal (test signal) transmitted in the same channel with the instantaneous value of a large-amplitude low-frequency signal (sweep signal) as the independent variable. For television systems, see Article 6.4 of GB4958.11. The differential gain (non-linearity) is defined as a function of the instantaneous value mentioned above, given by the following formula: DG(X)=
Where: DG(X) - differential gain,
X - instantaneous value of the input sweep signal;
A(X) - amplitude A of the output test signal with X as the independent variable.
A(X) - amplitude A of the output test signal when the sweep signal is zero. (6)
For an ideal device under test without distortion, the differential The gain (non-linearity) is zero. But for an actual device, the above function will appear to be variable. The actual device has the characteristic of differential gain (non-linearity) distortion (DG). DG is the difference between the limit values ​​of equation (6), usually expressed as a percentage as follows:
Amx=Aa×100%
The description of the relationship between differential gain and non-linearity and the selection of test signal frequency are given in Section 5.1.2. 5.1.2 Measurement method
A typical block diagram for measuring differential gain (non-linearity) is shown in Figure 4. It also includes the parts necessary for measuring differential phase. When measuring differential gain (non-linearity), the switch should be placed on the side where the amplitude modulation detector is selected. The baseband signal added to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a sweep signal. At the baseband output of the device under test, The test signal component is extracted and applied to the envelope detector. The envelope detector output, which is proportional to the amplitude of the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the sweep signal, or, if the device under test contains an IF and RF part, it can also come from the demodulation part of the IF signal. The sweep signal is a low-frequency signal, and its amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristics at any moment, the amplitude of the test signal should be much smaller than the amplitude of the sweep signal. The choice of test signal frequency depends on the part of the device under test to be examined, and it is usually much higher than the frequency of the sweep signal. When only the nonlinearity of the baseband part of the modulator and demodulator is examined, a relatively low frequency test signal is selected. If a test signal (e.g. between 50 and 500 kHz) is used, the measured value is called nonlinearity. When both the baseband part and the carrier part are to be examined, a test signal with a relatively high frequency
(e.g. within the range of 1 to 5 MHz) should be selected, and the measured value is called differential gain. Figure 4 Block diagram of differential gain (nonlinearity) and differential phase distortion measurement
1 - test signal generator, 2 - sweep signal generator, 3 device under test: 4 - bandpass filter; 5 - oscilloscope; 6 - amplitude modulation detector, 7 - phase modulation detector 5.1.3 Representation of measurement results
Differential gain (nonlinearity) distortion should preferably be represented by a photograph of the oscilloscope display, and the two axes should be appropriately calibrated; the horizontal axis should be calibrated with the sweep voltage, and if the device under test contains a modulator or demodulator, it should be calibrated with the frequency deviation. In addition, the distortion expressed as a percentage between the characteristic limit values ​​can also be given together with the sweep range expressed in megahertz. 5.1.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a.
Test signal frequency;
Sweep signal frequency,
Sweep amplitude expressed as peak-to-peak voltage or sweep width expressed as peak-to-peak frequency (MHz); c.
Maximum differential gain (non-linear) distortion allowed, expressed as a percentage. 5.2 Differential phase (group delay)
5.2.1 Definition and general considerations
Differential phase is the phase deviation measured by a small amplitude high frequency sinusoidal signal (test signal) transmitted in the same channel as a large amplitude low frequency signal (sweep signal) with the instantaneous value as the independent variable. For television systems, see GB4958.11, clause 6.5. Differential phase can be defined as a function of the instantaneous value above, given by the following equation: DP(X) = d(X)— in.
where: DP(x) is the differential phase;
is the instantaneous value of the input sweep signal,
d(X) is the phase of the output test signal with X as the independent variable; do
is the phase of the output test signal when the sweep signal is zero. (8)
For two ideal devices under test without distortion, the differential phase is zero. But for a real device, the above function will show a variation. Real devices have the characteristics of differential phase distortion (DP). DP is the difference between the limit values ​​of the above functions, usually expressed in (8
units, as follows:
GB/T4958.15—1992
DP-max -min () ....
Note: When a relatively low frequency (such as a few hundred kilohertz) test signal is used to measure the differential phase, the measurement also represents the change in the group delay of the intermediate frequency and radiation part of the device under test. In this case, the measurement equipment used is usually calibrated with group delay in nanoseconds (ns). The group delay and differential phase are proportional to the ratio of the test signal frequency. When a relatively high frequency (such as a few megahertz) test signal is used, the differential phase scale is mainly expressed in degrees.
5.2.2 Measurement method
The typical block diagram for measuring differential phase is shown in Figure 4, which also includes the parts necessary for measuring differential gain (nonlinearity). When measuring differential phase, the switch should be placed on the side where the phase modulation detection port is selected. The baseband signal applied to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a slowly varying swept frequency signal. At the baseband input of the device under test, the test signal component is extracted and applied to a phase detector. The phase detector output, which is proportional to the phase change of the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the swept signal or, if the device under test contains an IF or RF section, from the demodulated portion of the IF signal. The swept signal is a low frequency signal whose amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristic at any instant, the amplitude of the test signal should be much smaller than the amplitude of the swept signal. 5.2.3 Representation of measurement results
Differential phase distortion should preferably be represented by a photograph of the oscilloscope display. The two axes should be appropriately scaled: the horizontal axis should be scaled with the swept voltage and, if the device under test contains a modulator or demodulator, with the frequency deviation. In addition, the distortion expressed in degrees between the characteristic limits may also be given together with the sweep range expressed in volts or megahertz. 5.2.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. Test signal frequency,
Sweep signal frequency:
Sweep amplitude expressed in peak-to-peak voltage or sweep width expressed in peak frequency deviation (MHz); d.
Maximum allowable differential phase distortion, expressed in degrees. Additional notes:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 91 Definition and general considerations
Differential gain (non-linearity) is the incremental deviation measured by a small-amplitude high-frequency sinusoidal signal (test signal) transmitted in the same channel with the instantaneous value of a large-amplitude low-frequency signal (sweep signal) as the independent variable. For television systems, see GB4958.11, Article 6.4. The differential gain (non-linearity) is defined as a function of the instantaneous value mentioned above, given by the following formula: DG(X)=
Where: DG(X) - differential gain,
X - instantaneous value of the input sweep signal:
A(X) - amplitude A of the output test signal with X as the independent variable.
A(X) - amplitude A of the output test signal when the sweep signal is zero. (6)
For an ideal device under test without distortion, the differential gain (non-linearity) is zero. But for a practical device, The above function will appear to be variable. The actual device has the characteristic of differential gain (non-linearity) distortion (DG). DG is the difference between the limit values ​​of equation (6) and is usually expressed as a percentage as follows:
Amx=Aa×100%
The description of the relationship between differential gain and non-linearity and the selection of test signal frequency are given in Section 5.1.2. 5.1.2 Measurement method
A typical block diagram for measuring differential gain (non-linearity) is shown in Figure 4. It also includes the parts necessary for measuring differential phase. When measuring differential gain (non-linearity), the switch should be placed on the side where the amplitude modulation detector is selected. The baseband signal added to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a sweep signal. At the baseband output of the device under test, the test signal component is extracted and added to the envelope On the detector. The amplitude envelope detector output, which is proportional to the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the sweep signal, or, if the device under test contains an IF and RF part, it can also come from the demodulation part of the IF signal. The sweep signal is a low-frequency signal, and its amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristics at any moment, the amplitude of the test signal should be much smaller than the amplitude of the sweep signal. The choice of test signal frequency depends on the part of the device under test to be examined, and it is usually much higher than the frequency of the sweep signal. When only the nonlinearity of the baseband part of the modulator and demodulator is examined, a relatively low frequency test signal is selected (for example, at 50～500kHz), then the measured value is called nonlinearity. When both the baseband part and the carrier part are to be examined, a test signal with a relatively high frequency
(for example, in the range of 1～5MHz) should be selected, then the measured value is called differential gain. Figure 4 Block diagram of differential gain (nonlinearity) and differential phase distortion measurement
1-test signal generator, 2-sweep signal generator, 3 equipment under test: 4-bandpass filter; 5-oscilloscope; 6-amplitude modulation detector, 7-phase modulation detector 5.1.3 Representation of measurement results
Differential gain (nonlinearity) distortion should preferably be represented by a photograph of the oscilloscope display, and the two axes should be appropriately calibrated; the horizontal axis should be calibrated with the sweep voltage, and if the equipment under test contains a modulator or demodulator, it should be calibrated with the frequency deviation. In addition, the distortion expressed as a percentage between the characteristic limit values ​​can also be given together with the sweep range expressed in megahertz. 5.1.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a.
Test signal frequency;
Sweep signal frequency,
Sweep amplitude expressed as peak-to-peak voltage or sweep width expressed as peak-to-peak frequency (MHz); c.
Maximum differential gain (non-linear) distortion allowed, expressed as a percentage. 5.2 Differential phase (group delay)
5.2.1 Definition and general considerations
Differential phase is the phase deviation measured by a small amplitude high frequency sinusoidal signal (test signal) transmitted in the same channel as a large amplitude low frequency signal (sweep signal) with the instantaneous value as the independent variable. For television systems, see GB4958.11, clause 6.5. Differential phase can be defined as a function of the instantaneous value above, given by the following equation: DP(X) = d(X)— in.
where: DP(x) is the differential phase;
is the instantaneous value of the input sweep signal,
d(X) is the phase of the output test signal with X as the independent variable; do
is the phase of the output test signal when the sweep signal is zero. (8)
For two ideal devices under test without distortion, the differential phase is zero. But for a real device, the above function will show a variation. Real devices have the characteristics of differential phase distortion (DP). DP is the difference between the limit values ​​of the above functions, usually expressed in (8
units, as follows:
GB/T4958.15—1992
DP-max -min () ....
Note: When a relatively low frequency (such as a few hundred kilohertz) test signal is used to measure the differential phase, the measurement also represents the change in the group delay of the intermediate frequency and radiation part of the device under test. In this case, the measurement equipment used is usually calibrated with group delay in nanoseconds (ns). The group delay and differential phase are proportional to the ratio of the test signal frequency. When a relatively high frequency (such as a few megahertz) test signal is used, the differential phase scale is mainly expressed in degrees.
5.2.2 Measurement method
The typical block diagram for measuring differential phase is shown in Figure 4, which also includes the parts necessary for measuring differential gain (nonlinearity). When measuring differential phase, the switch should be placed on the side where the phase modulation detection port is selected. The baseband signal applied to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a slowly varying swept frequency signal. At the baseband input of the device under test, the test signal component is extracted and applied to a phase detector. The phase detector output, which is proportional to the phase change of the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the swept signal or, if the device under test contains an IF or RF section, from the demodulated portion of the IF signal. The swept signal is a low frequency signal whose amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristic at any instant, the amplitude of the test signal should be much smaller than the amplitude of the swept signal. 5.2.3 Representation of measurement results
Differential phase distortion should preferably be represented by a photograph of the oscilloscope display. The two axes should be appropriately scaled: the horizontal axis should be scaled with the swept voltage and, if the device under test contains a modulator or demodulator, with the frequency deviation. In addition, the distortion expressed in degrees between the characteristic limits may also be given together with the sweep range expressed in volts or megahertz. 5.2.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: ​​a. Test signal frequency,
Sweep signal frequency:
Sweep amplitude expressed in peak-to-peak voltage or sweep width expressed in peak frequency deviation (MHz); d.
Maximum allowable differential phase distortion, expressed in degrees. Additional notes:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China. This standard is under the jurisdiction of the Transmission Institute of the Ministry of Posts and Telecommunications.
This standard was drafted by the Beijing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafters of this standard are Wu Guanzhong and Shen Jianxiong. 91 Definition and general considerations
Differential gain (non-linearity) is the incremental deviation measured by a small-amplitude high-frequency sinusoidal signal (test signal) transmitted in the same channel with the instantaneous value of a large-amplitude low-frequency signal (sweep signal) as the independent variable. For television systems, see GB4958.11, Article 6.4. The differential gain (non-linearity) is defined as a function of the instantaneous value mentioned above, given by the following formula: DG(X)=
Where: DG(X) - differential gain,
X - instantaneous value of the input sweep signal:
A(X) - amplitude A of the output test signal with X as the independent variable.
A(X) - amplitude A of the output test signal when the sweep signal is zero. (6)
For an ideal device under test without distortion, the differential gain (non-linearity) is zero. But for a practical device, The above function will appear to be variable. The actual device has the characteristic of differential gain (non-linearity) distortion (DG). DG is the difference between the limit values ​​of equation (6) and is usually expressed as a percentage as follows:
Amx=Aa×100%
The description of the relationship between differential gain and non-linearity and the selection of test signal frequency are given in Section 5.1.2. 5.1.2 Measurement method
A typical block diagram for measuring differential gain (non-linearity) is shown in Figure 4. It also includes the parts necessary for measuring differential phase. When measuring differential gain (non-linearity), the switch should be placed on the side where the amplitude modulation detector is selected. The baseband signal added to the input of the device under test is a composite signal consisting of a sinusoidal test signal superimposed on a sweep signal. At the baseband output of the device under test, the test signal component is extracted and added to the envelope On the detector. The amplitude envelope detector output, which is proportional to the test signal, is used as the vertical deflection of the oscilloscope. The horizontal deflection of the oscilloscope comes directly from the sweep signal, or, if the device under test contains an IF and RF part, it can also come from the demodulation part of the IF signal. The sweep signal is a low-frequency signal, and its amplitude is selected to cover the entire dynamic range of the device under test. In order to seek a low average error in the measured characteristics at any moment, the amplitude of the test signal should be much smaller than the amplitude of the sweep signal. The choice of test signal frequency depends on the part of the device under test to be examined, and it is usually much higher than the frequency of the sweep signal. When only the nonlinearity of the baseband part of the modulator and demodulator is examined, a relatively low frequency test signal is selected (for example, at 50～500kHz), then the measured value is called nonlinearity. When both the baseband part and the carrier part are to be examined, a test signal with a relatively high frequency
(for example, in the range of 1～5MHz) should be selected, then the measured value is called differential gain. Figure 4 Block diagram of differential gain (nonlinearity) and differential phase distortion measurement
1-test signal generator, 2-sweep signal generator, 3 equipment under test: 4-bandpass filter; 5-oscilloscope; 6-amplitude modulation detector, 7-phase modulation detector 5.1.3 Representation of measurement results
Differential gain (nonlinearity) distortion should preferably be represented by a photograph of the oscilloscope display, and the two axes should be appropriately calibrated; the horizontal axis should be calibrated with the sweep voltage, and if the equipment under test contains a modulator or demodulator, it should be calibrated with the frequency deviation. In addition, the distortion expressed as a percentage between the characteristic limit values ​​can also be
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