This standard applies to the measurement of electrical characteristics of heterodyne transmitters for ground radio-relay systems, which do not include radio frequency channel division networks and switching networks. GB/T 4958.7-1988 Measurement methods for equipment used in ground radio-relay systems Part 2: Measurement of subsystems Section 7: Transmitters GB/T4958.7-1988 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T4958.7—1988
idtIEC 48727:1986
Methods of measurement for equipment used in terrestrial Radio-relay systems
Part 2:Measurements for sub-systems Section Seven-RadiotransmittersPromulgated on March 28, 1988
Implementation on February 1, 1989
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 Radio-relay systems
Part 2:Measurements for sub-systems Section Seven-Radiotransmitters sub-systems Section Seven-Radiotransmitters UDC
621.396:
621.317.08
GB/T4958.7—1988
IEC487—2—7(1986)
This standard is one of the national standards "Measurement methods for equipment used in ground radio-relay systems" series. This standard is equivalent to the International Electrotechnical Commission standard: IEC487-—2-7 (1986) "Measurement methods for equipment used in ground radio-relay systems Part 2: Subsystem measurements
1 Scope of application
Section Seven Transmitters"
This standard specifies the measurement methods for the electrical characteristics of heterodyne transmitters applicable to ground radio-relay systems, which do not include RF sub-channel networks and switching networks. Figure 1 is a functional block diagram of this type of transmitter, and the actual transmitter block diagram will be slightly different in details.
Intermediate short input
Local button
Figure 1 General block diagram of transmitter
Point to point
Although the noise of the local oscillator is an important indicator of the transmitter, it is usually not measured in the transmitter, but measured between the baseband terminal equipment of the radio relay system. This is because this indicator only forms baseband noise that is independent of path loss and is therefore not considered in this standard. 2 Radio frequency measurements
2.1 Output power
2.1.1 Definition and general considerations
The output power of a transmitter refers to the power provided to a nominal resistive load when an unmodulated intermediate frequency signal of a nominal frequency and a specified level is input to the transmitter input.
If the transmitter is equipped with an output power monitor, it should be calibrated with an instrument of known accuracy. 2.1.2 Measurement method
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
GB/T4958.7—1988
After the transmitter reaches a stable working state, add the unmodulated intermediate frequency signal to the input of the transmitter. Adjust the input signal level so that it is within the specified nominal level range (see Appendix A), connect the power meter directly to the output of the transmitter or connect the calibrated directional coupler to the output of the transmitter, and measure the output power corresponding to each input level. When using a directional coupler, all ports of the directional coupler should be well matched. If necessary, a calibrated attenuator and appropriate filter can be connected to the measurement arm of the directional coupler in front of the power meter to filter out parasitic noise, harmonics or other unnecessary signals. 2.1.3 Representation of results
The output power corresponding to each input signal level should be tabulated. The environmental conditions and power supply conditions during the measurement should also be noted. 2.1.4 Details to be specified
In the detailed equipment specification, the following items shall be included as required: a. Test points for output power,
b. Permissible range of output power;
c. Input level range with reference to the nominal value (e.g. 108dBm ± 2dB); d. Supply voltage limits;
e. Temperature range over which the equipment operates.
2.2 Spurious and harmonic output signals
The spurious and harmonic signals at the transmitter output shall be measured with an unmodulated intermediate frequency signal of nominal level applied to the transmitter input (see Annex B).
2.3 Local oscillator frequency
2.3.1 Accuracy
2.3.1.1 Definition and general considerations
The accuracy of the local oscillator frequency is defined as the maximum difference between the measured value and the nominal value under standard measurement conditions. The frequency accuracy of the local oscillator shall comply with the frequency tolerance specified in the technical specifications of the equipment. Note: The range specified in the radio regulations formulated by the International Telecommunication Union is the minimum frequency difference requirement. Each radio management department may specify a stricter frequency difference. 2.3.1.2 Measurement method
Connect the local oscillator directly to the digital frequency meter to measure its frequency. If there is a properly isolated test point, the measurement is best performed at this point (see Appendix C).
If the oscillator has neither a properly isolated measurement point nor an output terminal available, or if disconnecting the oscillator output terminal will cause the oscillator frequency to shift, the following method can be used for measurement. Connect the intermediate frequency signal with accurate frequency to the input terminal of the transmitter, and measure the RF output frequency fr at the output terminal of the transmitter. Then, according to the actual application, calculate the frequency of the local oscillator in ten or one. This requires that the stability of the frequency accuracy of the intermediate frequency signal generator is high enough to ensure that the overall accuracy meets the requirements. This measurement should be performed after the transmitter and the measuring instrument have reached stability. 2.3.1.3 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. Both expressions should indicate: the nominal frequency, the counting time of the frequency meter and the accuracy of the reference clock frequency. 2.3.1.4 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. The required accuracy;
c. The average counting time of the frequency meter (for example: 1 second); d. The accuracy of the frequency meter.
2.3.2 Stability
2.3.2.1 Definition
GB/T4958.7—1988
Stability is defined as: the maximum frequency change within a specified time interval and/or within the specified environmental conditions or power supply voltage range. 2.3.2.2 Measurement method
See 2.3.1.2 of this standard.
2.3.2.3 Expression of results
The measured frequency stability can be expressed in the following two ways: a. For example, within a specified time interval, the frequency stability of the local oscillator is 1.25×10-6. b. For example, when the power supply voltage changes by 60±12V, the frequency stability of the local oscillator is ±5kHz. 2.3.2.4 Details to be specified
In the detailed equipment specification, the following items should be included as required: a. The time interval for measurement;
b. Environmental conditions;
c. The range of power supply voltage variation;
d. The required stability;
e. The average counting time of the frequency meter (for example: 1 second). 2.4 Stabilization time
2.4.1 Definition and general considerations
The stabilization time of a transmitter refers to the time from the moment the transmitter is turned on to the moment when the main characteristics of the transmitter (local oscillator frequency, spurious signals, output power) have reached stability; that is, the time required to permanently meet the specified indicators. 2.4.2 Measurement method
The stabilization time of a transmitter is determined by measuring the following characteristics from the time the transmitter is turned on until they all reach stability. a. Local oscillator frequency;
b. Spurious signals;
c. Output power.
2.4.3 Representation of results
The stabilization time should be indicated.
2.4.4 Details to be specified
The maximum allowable stabilization time should be included in the detailed equipment specification, for example: 30 seconds. 3 Measurement in the intermediate frequency range
3.1 Input impedance and return loss
See GB6662-86 "Measurement methods for equipment used in ground radio relay systems Part 1: General for subsystems and simulation systems Section 3 Measurement of intermediate frequency range". Sometimes it is also required to measure the harmonics of the intermediate frequency. Measurement
4 Measurement from intermediate frequency to radio frequency
4.1 Amplitude/frequency characteristics and group delay/frequency characteristics Since there is a limiter in the transmitter under test, the measured amplitude/frequency characteristics only represent the performance of each level after the limiter. The amplitude-frequency characteristics from intermediate frequency to radio frequency are measured in accordance with Chapter 3 of GB6662-86. The measurement uses an intermediate frequency signal generator or an intermediate frequency swept signal generator, and the intermediate frequency detector is replaced by an radio frequency detector. When measuring the RF signal of a transmitter with an RF detector, it is necessary to sample through a well-matched directional coupler or RF attenuator so that the sampled signal does not exceed the maximum allowable input level of the RF detector. At the same time, it is also necessary to ensure that the detector and the directional coupler have a flat amplitude/frequency characteristic within the measured frequency band.
To measure the group delay/frequency characteristic from IF to RF (see GB6662-86), an RF to IF downconverter and an IF detector can be used to replace the RF detector. Connect the downconverter between the transmitter output and the IF input of the measuring instrument. 3
GB/T4958.7—1988
The IF signal level at the input of the transmitter under test should be adjusted to a level value within the nominal input level range of the transmitter. 4.2 AM/PM Conversion Coefficient
4.2.1 Definition and General Considerations
AM/PM conversion coefficient refers to the first-order derivative of the phase shift of the output signal with respect to the change in the input signal level at a given frequency. The AM/PM conversion coefficient of a transmitter can be measured by one of the following two measurement methods. Usually, this measurement is only performed during type approval. Note: ① The importance of this measurement depends on the receiver bandwidth limited by the system capacity and the RF channel spacing. ② When the intermediate frequency part of the transmitter has a limiter, this measurement is only related to the intermediate frequency part of the limiter. 4.2.2 Measurement Method
AM/PM conversion coefficient can be measured by either static method or dynamic method. 4.2.2.1 Static Method
The measurement block diagram is shown in Figure 2, in which a phase meter (such as a network analyzer or a vector voltmeter) is used to measure the phase change of the transmitter output signal caused by a change in the input signal level (for example, 1.0 dB). This measurement method is only applicable if the test point of the local oscillator can be connected to the downconverter so that the upconverter and the downconverter share the same local oscillator. Figure 2 Typical configuration for static measurement of the AM/PM conversion coefficient Before making this measurement, the phase shift error caused by the level change of the measuring instrument itself (especially the test attenuator, downconverter and phase meter) should be determined. In order to minimize the phase shift at the input of the transmitter, a suitable attenuator should be used. 4.2.2.2 Dynamic method The measurement block diagram is shown in Figure 3. In order to make this measurement on the transmitter, a frequency modulator and demodulator and a downconverter are required for the measurement. These devices are generally installed in the current commercial line analyzers. The residual AM/PM conversion of the measuring equipment should be negligible compared with the measured value. The switch "S" can be used to connect or disconnect the test network with the known group delay frequency characteristics to the input of the transmitter under test, and the relative change "△" of the amplitude of the measured signal after demodulation can be measured. The amplitude modulation/phase modulation conversion coefficient "k" can be calculated using the following formula. 4958.7—1988
——The first derivative of the group delay frequency characteristic of the test network, the frequency is expressed in radians/second. The test network usually has a parabolic group delay/frequency characteristic. In this case, both and are proportional to the frequency difference with the center frequency as the reference, so (1) can be simplified to: k=10.5A1
Where: A-
-the first slope of the differential gain characteristic curve of the transmitter under test, %/MHz;-parabolic group delay coefficient, ns/(MHz)2T2
k——AM/PM conversion coefficient, /dB, f.-test frequency, MHz. bzxz.net
Note: Formula (2) It is only valid when k is a constant. The positive amplitude modulation/phase modulation conversion coefficient k represents the lagging phase modulation caused by the positive amplitude modulation.
It can be seen from the above formula that the error depends on the accuracy of 2 and A, and the errors of these quantities must be negligible. If the test frequency is too low, the sensitivity of the measuring device is not enough; conversely, if the frequency is too high, it will cause a large average error. The best test frequency depends on the bandwidth being tested, and it is usually appropriate between 2 and 3MHz. 4.2.3 Representation of results
The measured results should be expressed in "degrees per decibel", preferably using a graph of the amplitude modulation/phase modulation conversion coefficient as a function of the input signal level.
4 .2.4 Details to be specified
In the detailed equipment specification, the following items should be included as required: a. The measurement method used (static method or dynamic method); b. Intermediate frequency input level,
c. AM/PM conversion tolerance;
d. The limit value of the power supply voltage;
e. The temperature range in which the equipment operates.
5 Carrier frequency reset
When there is a carrier frequency reset at the transmitter input, the measurement of this indicator should be carried out in accordance with the method specified in Article 4.5 of GB4958.888 "Measurement methods for equipment used in ground radio relay systems Part 2: Subsystem measurements Section 8 Receivers". 5
GB/ T4958.7—1988
Appendix AD
Intermediate frequency characteristics of simulated radio-relay system switching (supplement)
A.1 Output and input voltages of intermediate frequency signals
Nominal values
Output: +5.2dBm (0.5Vr.ms)
The voltage at the output of the receiver corresponds to the nominal RF level at the input of the receiver. Input: +0.8dBm (0.3Vr.ms)
A.2 Intermediate frequency nominal impedance
Level variations beyond the above range due to variations in the received signal or due to phenomena not related to propagation shall be determined by agreement between the relevant competent authorities.
By agreement between the relevant competent authorities, switching between the output and input terminals may be carried out within the input voltage range from 0.5Vr·m·s to 0.3Vr·m·s. Necessary adjustments shall be made by the relevant competent authorities at the input. Appendix B
Measurement method of spurious and harmonic output signals (supplement)
The measurement method used depends on whether the in-band spurious signals and harmonics and out-of-band spurious signals are measured. B.1 In-band spurious signals and harmonics measurement method The measurement block diagram is shown in Figure B1-1, in which the spectrum analyzer can be replaced by a frequency-selective level meter. Chinese Dunhua Xue
Hey generator
Makeup in the machine
Deficiency analysis and
Figure B1 Block diagram for measuring in-band spurious signals and harmonics The dynamic range of the spectrum analyzer should not be less than 70dB. Its amplitude/frequency characteristics should be uniform and flat. If the output level of the device under test is low, for example, less than 0dBm, a low-noise amplifier can be used to amplify it to the input level range of the spectrum analyzer. Special attention should be paid to the measured signal level not to exceed the allowable input level of the spectrum analyzer to prevent the spectrum analyzer from overloading itself and producing significant intermodulation products.
In some cases, the RF carrier frequency can overload the spectrum analyzer. At this time, the block diagram shown in Figure B2 can be used to measure the in-band spurious signal. When measuring harmonics, the input impedance of the spectrum analyzer or frequency-selective level meter at the harmonic frequency should match the output impedance of the device under test. If the output of the transmitter under test is a waveguide, a converter with an appropriate interface should be used. B.2 Out-of-band spurious signal measurement method
The out-of-band spurious signal measurement device is shown in Figure B2. The center frequency of the bandpass filter is the transmitter output carrier frequency, and the bandpass filter ① This appendix is ​​written in accordance with the recommendation 403-3 of the International Electrotechnical Consultative Committee CCIR. ②: This appendix is ​​written in reference to Article 15 of the International Electrotechnical Commission standard IEC487-1-2. 6
GB/T4958.7—1988
The bandwidth of the circulator should be less than the nominal bandwidth of the transmitter under test, and its out-of-band return loss can be ignored. Middle
Outgoing Circulator
New Receiver of Haiyuji
Figure B2 Block diagram of measurement of out-of-band spurious signals Connect a short circuit to the A-end interface of the circulator to calibrate the spectrum analyzer, and then change the A-end to the side of the bandpass filter. At this time, the carrier frequency level on the spectrum analyzer should be reduced by at least 30dB. Appendix
Measurement method of local oscillator frequency
(Supplement)
The general device for measuring the local oscillator frequency is shown in Figure C1. 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 spurious signals, it is best to add a bandpass filter to the output of the local oscillator for measurement.
Zhongkong meter resources
Huiyuan device
Local oscillator frequency measurement configuration
Before measurement, the local oscillator and the measuring instrument to be measured should reach a thermally stable working state. If possible, the surrounding energy processing device should stop working to ensure the accuracy of the measurement. Then read the reading of the digital frequency meter at 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 practical purposes, recording one hundred times is enough. However, this number depends on whether there is noise and modulation. Usually, it is sufficient to analyze the statistical average value within several measurement time intervals to prove that the results are repeatable.
① This appendix is ​​written in accordance with Article 9 of IEC487-1 approved by the International Electrotechnical Commission. 7
Additional notes:
GB/T4958.7-1988
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 Xi'an Microwave Equipment Factory of the Ministry of Posts and Telecommunications and the Institute of Standardization of Posts and Telecommunications Industry of the Ministry of Posts and Telecommunications. The main drafters of this standard are: Zhou Haokai, Dong Fukang, and Qiu Yan.
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