This standard specifies the measurement methods for the electrical characteristics of receivers (excluding channel splitting networks and switching networks) applicable to ground radio-relay systems. The box in Figure 1 is a functional block diagram of this type of receiver. The actual receiver block diagram may differ in details, for example, some functional blocks such as the radio frequency amplifier may be omitted. GB/T 4958.8-1988 Measurement methods for equipment used in ground radio-relay systems Part 2: Measurement of subsystems Section 8: Receivers GB/T4958.8-1988 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T4958.8—1988
idtIEC487—2—8：1986
Methods of measurement for equipment used in terrestrial Radiorelay systems
Part 2:Measurements for sub-systems Section Eight Radio receivers
Promulgated on March 28, 1988
Implementation on February 1, 1989
Promulgated by the Ministry of Posts and Telecommunications of the People's Republic of China
National Standard of the People's Republic of China
Methods of measurement for equipment used in terrestrial Radiorelay systems
Part 2: Measurements for sub-systems SectionEightRadio receivers
621.396：
621.317.08
GB/T4958.8—1988
IEC487—2—8(1986)
This standard is one of the national standards "Measurement methods for equipment used in ground radio-relay systems" series of standards. This standard is equivalent to the International Electrotechnical Commission standard IEC487 method, Part 2: Measurements for sub-systems Section 8 Receivers" 1 Scope
-8 (1986) "Measurement of equipment used in ground radio-relay systems This standard specifies the measurement methods for the electrical characteristics of receivers (excluding sub-channel networks and switching networks) applicable to ground radio-relay systems. The block diagram of Figure 1 is a functional block diagram of this type of receiver. The block diagram of an actual receiver may differ in details, for example, some functional blocks such as the RF amplifier may be omitted.
1. RF channel filter
5. Pre-IF amplifier
2. RF amplifier
3. Mixer
6. IF filter
8. Main IF amplifier (with AGC)
4. Local oscillator
7. Amplitude and group delay equalizer
Figure 1 General block diagram of receiver
Although the noise of the local oscillator is an important indicator of the receiver, it is usually not measured in the receiver, but in the baseband terminal equipment of the radio relay system. Since this indicator only forms baseband noise that is independent of path loss, it is not considered in this standard.
2 RF Measurement
2.1 Local Oscillator Frequency
Approved by the Ministry of Posts and Telecommunications of the People's Republic of China on March 28, 1988 and implemented on February 1, 1989
2.1.1 Accuracy
2.1.1.1 Definition and General Considerations
GB/T4958.8—1988
The accuracy of the local oscillator frequency refers to the maximum tolerance between the value measured under standard test conditions and the nominal value. The frequency accuracy of the local oscillator shall comply with the frequency deviation specified in the technical specifications of the equipment. 2.1.1.2 Measurement Method
The local oscillator can be directly connected to a digital frequency meter to measure its frequency. If there is a properly isolated measurement point, it is best to measure at that point, see Appendix A.
If there is no suitable isolated measurement point and no oscillator output terminal is available, or if disconnecting the output port of the local oscillator will cause the oscillator frequency to shift, the following method can be used for measurement. Connect the RF signal generator to the input of the receiver and measure the RF input frequency f and the intermediate frequency output frequency . Then, according to the actual application, calculate the frequency f10 of the local oscillator from f+f or f-fu. The stability of the RF signal generator frequency must be high enough to ensure that the overall accuracy requirements are met.
2.1.1.3 Expression of results
The measured accuracy can be expressed as an absolute value, for example: 50kHz, or as a relative value, for example: 25×10-6. The nominal frequency should be indicated in both expressions.
2.1.1.4 Details to be specified
In the detailed equipment specification, the following items should be included as required, a. The nominal frequency of the local oscillator;
b. Required accuracy,
c. Average counting time of the frequency meter (e.g. 1 second); d. Accuracy of the frequency meter
2.1.2 Stability
2.1.2.1 Definition
Stability refers to the maximum frequency change within a specified time interval and (or) under specified environmental conditions or within the range of power supply voltage changes.
2.1.2.2 Measurement method
See 2.1.1.2 of this standard.
2.1.2.3 Representation of results
The measured stability shall be expressed in the following two ways: a. For example, within a specified time interval, the stability of the local oscillator frequency is 1.25×10-6. b. For example, when the power supply voltage changes by 60±12V, the stability of the local oscillator frequency is ±5kHz. 2.1.2.4 Details to be specified
In the detailed equipment specification, the following items should be included as required: a. Time interval for measurement;
b. Environmental conditions
c. Supply voltage variation range;
d. Required stability;
e: Average counting time of the frequency meter (for example: 1 second)2.2 RF spurious signals
2.2.1 Definition
Spurious signals are those spurious frequencies generated by the receiver and appearing at the receiver input. The most important of these are spurious signals caused by local oscillator leakage.
2.2.2 Measurement method
It is best to use a calibrated spectrum analyzer and connect it to the input of the receiver for measurement. 2
2.2.3 Presentation of results
GB/T4958.8—1988
The measurement results may be presented in the form of a table of the frequencies of the spurious signals and their absolute level (dBm), or in the form of a graphic display on a suitable spectrum analyser with a calibrated scale.
2.2.4 Details to be specified
The following items shall be included in the detailed equipment specification as required: a. The frequency band of the spurious signals to be measured;
b. The permissible level of the spurious signals;
c. The specified spurious signal measurement points;
2.3 Amplitude/frequency characteristics of RF channel filters (if the filters are not included in the sub-channel network) 2.3.1 General considerations
This measurement is usually only required for type testing. 2.3.2 Measurement method
The swept frequency method is preferably used for measurement. Connect the input of the measured channel filter to a swept frequency signal generator: its output is sent to a tracking selective level meter or a broadband detector with a flat amplitude/frequency characteristic for measurement. Alternatively, the point-by-point method can be used for measurement. For either method, the corresponding instruments are available on the market. 2.3.3 Representation of results
The results of the swept frequency measurement should be presented in a photograph or drawn as an X-Y coordinate curve. When the measurement results are not represented graphically, they should be represented in the following way:
"Amplitude/frequency characteristics: within the range of 6.0 to 6.4 GHz, the amplitude relative to 6.2 GHz is within +0.2 to -0.1 dB". The results of point-by-point measurement can be presented in a table or as described above. When the fluctuation components are easily identifiable, the measurement results of each of these amplitude (expressed in decibels of peak-to-peak value) and frequency (expressed in megahertz) characteristics must be presented.
2.3.4 Details to be specified
In the detailed equipment specification, a characteristic curve describing the relationship between insertion loss and frequency shall be included, which is drawn based on the loss at the center frequency point.
3 Measurements in the intermediate frequency range
3.1 Output impedance and return loss
See Chapter 1 of GB6662-86 "Measurement methods for equipment used in ground radio relay systems, Part 1: Measurements common to subsystems and simulation systems, Section 3 Measurements in the intermediate frequency range". 4 Measurements from RF to intermediate frequency
4.1 Amplitude/frequency characteristics and group delay/frequency characteristics These characteristics are meaningful only if the intermediate frequency equalizer (usually used for equalization between a relay segment) can be excluded from the measurement. The measurement is carried out according to the methods given in Articles 3.2 and 6.2 of GB6662-86. However, the intermediate frequency swept frequency generator should be replaced by an RF swept frequency signal generator.
When measuring the amplitude/frequency characteristics, care should be taken to disable the automatic gain control circuit and manually adjust the gain control voltage so that it is compatible with the input level applied by the swept frequency signal generator. 4.2 Noise figure
4.2.1 Definition
The noise figure (F) refers to the ratio of the signal-to-noise ratio at the receiver input to the signal-to-noise ratio at the receiver output under the same bandwidth conditions: F
(S/N)
Where: S is the signal power.
GB/T4958.8—1988
N—Noise power: In (S/N), N is the effective noise power or the load of the nominal impedance at 290K as the reference temperature. F—Noise figure, dB.
According to this definition, the noise figure can also be expressed as the ratio of the noise power actually present at the output of the receiver to the noise power present at the output when the receiver does not introduce noise. 4.2.2 Measurement method
In the measurement configuration shown in Figure 2, the .3dB intermediate frequency fixed attenuator and the continuously variable RF attenuator should be accurately calibrated. The measurement should be performed at the input of the receiver channel filter. If the channel filter is part of the channeling network (i.e., it is not part of the receiver), a substitute channel filter should be connected to the receiver input. Before making the measurement, the automatic gain control circuit of the receiver should be disabled and the intermediate frequency gain should be manually adjusted so that it is adapted to the input level of the noise figure to be measured. a ts
Typical configuration for measuring noise figure
The noise figure should be measured according to the following steps: a. Use a power meter or IF level meter with sufficient sensitivity to measure the output level of the receiver. Turn off the known noise source and short-circuit the 3dB IF fixed attenuator. Care must be taken to ensure that under this condition, the impedance of the noise source and its related devices are in a matching state. b. Connect the 3dB IF fixed attenuator, turn on the noise source, and adjust the RF variable attenuator so that the IF level meter reaches the same reading as item a.
c. If β (expressed in decibels) is the attenuation value introduced by the RF variable attenuator, the noise figure can be calculated as follows: F(dB)=α—β
Where: α (expressed in decibels) is the noise source constant. α=10 1g(290
Where: T is the noise source temperature K.
Note: ① Formula (2) is applicable only when the RF attenuator temperature is 290K. ② Use a gated noise source tester available on the market to directly display the noise figure. 4.2.3 Representation of results
The measurement results should be expressed as the noise figure measured under the conditions of specified receiver input level, or as a curve of the measured noise figure as a function of the receiver input level. 4.2.4 Details to be specified
In the detailed equipment specification, the following items should be included as required: a. Receiver input level range, for example: -40 to -75dBm, b. The maximum noise figure allowed corresponding to one or several specified receiver input levels ; c. The receiver input terminal related to the noise figure. 4.3 Selectivity
4.3.1 Definition
Selectivity refers to the ability of the receiver to select and identify useful signals from useful signals and useless signals coexisting with them. 4.3.2 Measurement method
GB/T4958.8—1988
A directional coupler can be replaced by an RF hybrid connector. Figure 3 Measurement configuration of receiver selectivity
In the measurement configuration shown in Figure 3, the frequency of RF signal generator 2 is adjusted to a frequency consistent with the nominal frequency of the receiver to simulate useful signals, and RF signal generator 1 simulates useless signals. When measuring at the input terminal of the receiver channel filter, the following steps should be followed: a. Turn the RF signal Remove the RF signal generator 1, set the RF variable attenuator 1 to maximum attenuation, and adjust the RF variable attenuator 2 until the useful signal at the receiver input reaches the specified value. b. Reconnect the RF signal generator 1 and tune its frequency to a frequency close to that of the RF signal generator 2, but it must be distinguishable on the spectrum analyzer.
c. Adjust the RF variable attenuator 1 until the level of the useless signal at the receiver input (and thus the level at the output) is much lower than the level of the useful signal to prevent changes in the automatic gain control level. d. Then change the frequency ft of the RF signal generator 1 within an appropriate range and measure the ratio between the useless signal level at the receiver output and the reference level recorded in item 1 on the spectrum analyzer. The frequency of the useless signal should also be measured. For selectivity It is particularly important to generate those RF frequencies that fall within the receiver intermediate frequency amplifier passband. These frequencies are: a. f = f10 ± f (receiver nominal frequency) f-f10 dry f (image frequency)
b.fu = f1o (local oscillator frequency)
c.fu-f1 ± nfu
d.fuf1 ±
Usually, the measurement is repeated several times at different useful signal input levels within the specified receiver input level range, so that the frequency components of the unwanted signals that fall within the receiver intermediate frequency passband after combining with the useful signal (such as various combinations of items b and c) can be easily found.
4.3.3 Representation of results
The selective measurement results are best presented in a graph. The graph is within the specified frequency range. The ratio of the useful and unwanted output signal levels is plotted as a function of frequency.
4.3.4 Details to be specified
In the detailed equipment specification, the following items shall be included as required: a. Input level of the applied useful signal;
b Input level and frequency of the applied unwanted signal(s) c. Required selectivity (frequency response curve or output level range of relevant frequencies). 4.4 Static automatic gain control characteristics
4.4.1 Definition
The static characteristics of the receiver automatic gain control are expressed as a curve of the relationship between output level and input level. The input and output levels are expressed in decibels relative to 1 mW, and the input signal frequency is the nominal input frequency. 4.4.2 Measurement method
Figure 4 shows a suitable measurement configuration. An RF signal generator with a frequency close to the nominal input frequency of the receiver is sent to the input of the receiver via an RF variable attenuator with a calibrated scale. 5
GB/T4958.8—1988
Adjust the output level of the RF variable attenuator and the RF signal generator to make the receiver input level the maximum value. Then, increase the attenuation within the specified range and record the reading on the level meter. Point number
Figure 4 Configuration for measuring the static automatic gain control characteristics 4.4.3 Representation of results
Figure 5 Example of static characteristics of automatic gain control
The measurement results can be given by the graph shown in Figure 5, or can be expressed as follows: When the receiver input level is -20 to -70 dBm, the receiver output level is within +5.0 to +3.2 dBm. 4.4.4 Details to be specified
In the detailed equipment specification, the following items should be included according to requirements: a. The allowable variation range of the receiver output level; b. The range of the RF input level;
c. The location of the input connection point.
4.5 IF Squelch and Carrier Frequency Reset
4.5.1 General Considerations
During IF switching, when the signal-to-noise ratio at the receiver output drops below a certain specified level, the IF signal at the receiver output is usually suppressed and replaced by the output of an IF oscillator. Another option is that the output of the IF oscillator is inserted at the input of the transmitter. In this case, the insertion of the IF oscillator can be controlled by the receiver squelch logic circuit or by the reduction of the transmitter IF input level.
The purpose of this type of device is to prevent harmful interference caused by high-level broadband noise in adjacent channels from being added to the subsequent transmitter. In addition, when the receiver is suppressed, the local IF oscillator is inserted to ensure the transmission of sub-baseband or super-baseband business channels on the subsequent relay segment.
4.5.2 Startup and recovery levels
4.5.2.1 Definition
GB/T4958.8—1988
The squelch start level refers to the input power level of the receiver when the squelch is activated and an alarm is provided. The squelch recovery level refers to the level when the intermediate frequency squelch is released. Note: ① The start level can usually be adjusted within a specified range. ② The specified recovery level is x dB higher than the start level, and sometimes X is adjustable. 4.5.2.2 Measurement method
Connect the RF signal generator simulating the received signal to the receiver input through a calibrated continuously variable attenuator. Continuously reduce the input signal level to a frequency close to the nominal frequency of the receiver until the intermediate frequency squelch is activated. Then, continuously increase the input signal level until the squelch is released.
4.5.2.3 Presentation of results.
The start and recovery levels shall be tabulated.
4.5.2.4 Details to be specified
In the detailed equipment specification, the following items shall be included as required: a. Start level range, for example: -70 to -80 dBm, b. Recovery level or recovery level range, for example: 5 dB above the start level, or 510 dB above the start level. 4.5.3 Start-up time
4.5.3.1 Definition
The squelch start-up time is the time interval from the moment the receiver input power drops below the IF carrier reset start level to the moment the receiver IF input signal is replaced by the IF substitute signal. Note: This measurement is important when the carrier reset start time affects the operation of the standby channel switching equipment. 4.5.3.2 Measurement method
The measurement configuration shown in Figure 6 can be used. The receiver input signal level is adjusted to a specified value (for example: -40dBm), and the start level is also adjusted to a specified value. Then, a periodically interrupted input signal is obtained by driving the RF switch with a trigger signal generator. The opening time of the RF switch should be longer than the measured start-up time. Usually, the switching repetition frequency is 10 to 100Hz. The start-up time is measured by using a calibrated oscilloscope to measure the time interval between the moment the switch interrupts the receiver's RF signal (corresponding to the moment the normal IF signal on the oscilloscope ends) and the moment the IF substitute signal is inserted. Figure 6 Configurator for measuring IF squelch and carrier frequency reset Figure 7 shows an example of measuring the IF carrier frequency reset start time. For this measurement, an IF solid state switch can be used instead of an RF switch. The IF switch should be placed between the pre-IF amplifier and the main IF amplifier. 7
GB/T4958.8—1988
Start-up time
Lewendong
China Ball Corporation
Figure 7 Oscilloscope display of the measurement of the IF squelch and carrier frequency reset start-up time 4.5.3.3 Representation of results
The measurement results are preferably presented as a graphic display of an oscilloscope with a calibrated scale, or the start-up time can be described in words. 4.5.3.4 Details to be specified
In the detailed equipment specification, the following items should be included as required: a. Receiver input level (for example: -40dBm); b. IF squelch start-up level (or level range); c. Maximum allowable start-up time.
4.5 .4 Level and frequency of the intermediate frequency substitute signal 4.5.4.1—General considerationsWww.bzxZ.net
When the receiver input level is lower than the intermediate frequency squelch start level, the level and frequency of the intermediate frequency substitute signal should be measured at the receiver output. 4.5.4.2 Measurement method and expression of results
See Articles 2.2, 8.1 and 8.2 of GB6662-86. 4.5.4.3 Details to be specified
In the detailed equipment specification, the following items should be included as required: a. The allowable range of the intermediate frequency substitute signal level (for example: +2 to +5dBm); b. The required frequency accuracy of the intermediate frequency substitute signal. 8
GB/T4958.8—1988
Appendix AD| |tt||Method for measuring the frequency of the local oscillator
(Supplement)
The general configuration for measuring the frequency of the local oscillator is shown in Figure A1. The attenuator is used to ensure that the measured level is within the allowable input level range of the digital frequency meter. If there are parasitic signals, it is best to add a bandpass filter to the output of the local oscillator for measurement. Replace the test vehicle machine
Liquid measurement point
Band-made wave grid
Digital pointer training
Figure A1 General configuration for measuring the frequency of the local oscillator Before measurement, the local oscillator and the measuring instrument under test should reach a thermally stable working state. If possible, the surrounding energy processing devices should stop working to ensure accurate measurement. Then read the digital The reading of the frequency meter within the counting time (for example: 1 second). Another method is to use a recorder to record the numbers displayed by the digital frequency meter. For actual situations, recording one hundred times is sufficient, but this number depends on whether there is noise and modulation. Usually, it is sufficient to analyze the statistical average value within a few measurement time intervals to prove that the results are repeatable.
Additional notes:
This standard is under the jurisdiction of the Post and Telecommunications Industry Standardization Institute of the Ministry of Posts and Telecommunications. This standard was drafted by the Xi'an Microwave Equipment Factory of the Ministry of Posts and Telecommunications and the Post and Telecommunications Industry Standardization Institute of the Ministry of Posts and Telecommunications. The main drafters of this standard: Dong Fukang, Zhou Haokai, Qiu Yan. ① This appendix is ​​written in accordance with Article 9 of the International Electrotechnical Commission Standard EC487-1. 98—1988
Appendix AD
Method for measuring the frequency of a local oscillator
(Supplement)
The general arrangement for measuring the frequency of a local oscillator is shown in Figure A1. The attenuator is used to ensure that the measured level is within the permissible input level range of the digital frequency meter. If there are spurious signals, it is best to add a bandpass filter to the output of the local oscillator for measurement. Change the measuring vehicle
Liquid measuring point
Band wave grid
Digital pointer
Figure A1 General arrangement for measuring the frequency of a local oscillator Before the measurement, the local oscillator under test and the measuring instrument should reach a thermally stable working state. If possible, the surrounding energy processing equipment should be stopped to ensure accurate measurement. Then read the reading of the digital frequency meter within the counting time (for example: 1 second). Another method is to use a recorder to record the number displayed by the digital frequency meter. For practical purposes, one hundred recordings are sufficient, but this number depends on the presence or absence of noise and modulation. Usually, it is sufficient to analyze the statistical average value within a few measurement time intervals to prove that the results are repeatable.
Additional Notes:
This standard is under the jurisdiction of the Post and Telecommunications Industry Standardization Institute of the Ministry of Posts and Telecommunications. This standard was drafted by the Xi'an Microwave Equipment Factory of the Ministry of Posts and Telecommunications and the Post and Telecommunications Industry Standardization Institute of the Ministry of Posts and Telecommunications. The main drafters of this standard are Dong Fukang, Zhou Haokai, and Qiu Yan. ① This appendix is ​​written in accordance with Article 9 of the International Electrotechnical Commission Standard EC487-1. 98—1988
Appendix AD
Method for measuring the frequency of a local oscillator
(Supplement)
The general arrangement for measuring the frequency of a local oscillator is shown in Figure A1. The attenuator is used to ensure that the measured level is within the permissible input level range of the digital frequency meter. If there are spurious signals, it is best to add a bandpass filter to the output of the local oscillator for measurement. Change the measuring vehicle
Liquid measuring point
Band wave grid
Digital pointer
Figure A1 General arrangement for measuring the frequency of a local oscillator Before the measurement, the local oscillator under test and the measuring instrument should reach a thermally stable working state. If possible, the surrounding energy processing equipment should be stopped to ensure accurate measurement. Then read the reading of the digital frequency meter within the counting time (for example: 1 second). Another method is to use a recorder to record the number displayed by the digital frequency meter. For practical purposes, one hundred recordings are sufficient, but this number depends on the presence or absence of noise and modulation. Usually, it is sufficient to analyze the statistical average value within a few measurement time intervals to prove that the results are repeatable.
Additional Notes:
This standard is under the jurisdiction of the Post and Telecommunications Industry Standardization Institute of the Ministry of Posts and Telecommunications. This standard was drafted by the Xi'an Microwave Equipment Factory of the Ministry of Posts and Telecommunications and the Post and Telecommunications Industry Standardization Institute of the Ministry of Posts and Telecommunications. The main drafters of this standard are Dong Fukang, Zhou Haokai, and Qiu Yan. ① This appendix is ​​written in accordance with Article 9 of the International Electrotechnical Commission Standard EC487-1. 9
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