This standard is applicable to the measurement of baseband noise performance of simulated radio relay systems for transmission of frequency division multiplexed (FDM) telephones. These measurements are signal-dependent. It is a supplement to the items listed in GB4958.9 "Methods of measurement for equipment used in terrestrial radio relay systems Part 3: Measurements for simulated systems Section 2 Baseband measurements". The measurements specified in Section 2 are generally applicable to the transmission of telephone, television and sound programs. GB/T 4958.12-1988 Methods of measurement for equipment used in terrestrial radio relay systems Part 3: Measurements for simulated systems Section 4: Measurements for frequency division multiplexed transmissions GB/T4958.12-1988 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T4958.12—1988
idtIEC487-3-4:1982
Methods of measurementfor equipmentUsed in terrestrial radio-relay systemsPart 3: Measurements on simulated systems
Section 4
Measurements for frequency-division multiplexed transmission
Methods of measurementfor equipmentUsed in terrestrial radio-relay systemsPart 3:Simulated systems
Section Four-Measurements for fdm transmissionPublished on March 28, 1988
Implemented 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 measurementfor equipmentUsed in terrestrial radio-relay systemsPart 3: Measurements on simulated systems
Section 4-Measurements for frequency-division multiplexed transmission
Methods of measurement for equipmentUsed in terrestrial Radio-relay systems Part 3: Simulated systems Section Four-Measurements for FDM transmission UDC 621.317.08 GB/T 4958.12—1988 IEC 487—3—4 (1982) This standard is one of the national standards in the series of "Measurement methods for equipment used in terrestrial radio-relay systems". This standard is equivalent to the International Electrotechnical Commission (IEC) standard 487—3—4 (1982) "Measurement methods for equipment used in terrestrial radio-relay systems Part 3: Measurements of simulated systems Section 4 Measurements of frequency division multiplexed transmission". 1 Scope of application This standard applies to the measurement of baseband-to-baseband noise performance of simulated radio-relay systems transmitting frequency division multiplexed (FDM) telephones. These measurements are related to the signal. It is a supplement to the items listed in GB4958·988 "Methods of measurement of equipment used in terrestrial radio-relay systems Part 3: Measurement of simulation systems Section 2 Baseband measurements". The measurements specified in Section 2 are generally applicable to the transmission of telephone, television and sound programs.
2 Definitions and general considerations
The noise loading performance of the system is the noise power measured in a selected narrowband measurement channel when a uniform spectrum random noise (white noise) of a normal load level (see 2.1) is added to the baseband. This measurement channel simulates an unloaded voice channel. The white noise added to the baseband input of the system under test is limited to the frequency band occupied by the telephone channel capacity by high-pass and low-pass filters. The noise measurement channel is provided by a narrowband stop filter. Different filters can be selected to measure noise performance at several frequencies (including those located near the low end, middle and high end of the baseband frequency range).
At the system output, the total noise in a noise measurement channel includes basic noise and intermodulation noise (sometimes called idle noise and distortion noise, respectively). In order to obtain the total noise and basic noise respectively, the usual practice is to measure the noise of each noise measurement channel when the noise load is added to its baseband and when the noise load is not added to the baseband. The intermodulation noise can be obtained from the measured results. Noise performance can be expressed in terms of noise power ratio (npr), signal-to-noise ratio, and noise power units or noise power levels relative to the zero relative level point of the system. The units used can be pico (pW), decibels above 1pW or decibels below 1mW, which can be specified as weighted values ​​or unweighted values. The definition of noise power ratio is the ratio of the noise power in the measurement channel when the baseband is fully loaded with noise to the noise power in the channel when all basebands except the measurement channel are loaded with noise (i.e., total noise). Or the ratio of the noise power in the measurement channel when all basebands are unloaded (i.e., basic noise). The noise power ratio is always expressed in positive decibels. The definition of signal-to-noise ratio is the ratio of the standard test tone power (0dBm0) to the noise power within the specified noise measurement channel bandwidth for the same point of the circuit. The measured signal-to-noise ratio can be weighted or unweighted. The signal-to-noise ratio is expressed in positive decibels. For the conversion between several commonly used noise load measurement units, please refer to Appendix A. 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 Conventional load
GB/T4958.12—1988
The conventional load levels applicable to certain typical voice channel capacities specified by the International Telegraph and Telephone Consultative Committee (CCITT) (Appendix BB.1) and recommended by the International Radio Consultative Committee (CCIR) (Appendix BB.2) are listed in Table 1. The average power level Lc of conventional loads for other voice channel capacities can be calculated by the following formula: Lc=—15+10lgN(dBmOp).
Lg=-1+4lgN(dBmOp).
Where N is the voice channel capacity of the radio relay system. N≥240
12N<240
Note: ① These levels simulate the average power level of voice transmitted on the system when the circuit is busy, plus various signaling currents, etc. When the main part of the baseband is used to transmit audio telegrams or data, these formulas are not applicable; ② When N≥60, the results calculated by equations (1) and (2) are very close to the actual signal. However, for smaller channel capacity, the authenticity of the white noise test is poor due to the different properties of the actual signal and the test signal. Table 1 Conventional load level
Number of channels
Relative power level at point R'
Conventional load level
Nominal level of test signal at point R'
Conventional load radio relay system uses a uniform spectrum random noise signal as the load. The load of the system is adjusted to the conventional load level. The frequency band of the noise signal is limited to correspond to the total bandwidth of the frequency division multiplexed signal. In most cases, the test signal level is selected to be equal to the conventional load.
2.2 Noise components
In GB4958·10-88 "Measurement methods for equipment used in ground radio-relay systems Part 3: Measurement of simulated systems Section 1 General Principles" and Appendix BB.1, various types of noise present in radio-relay systems are summarized. In the baseband of the simulated radio-relay system, the measured total noise includes the following three components: a.
Residual noise that is independent of path loss and load, which generally refers to the basic noise that is independent of path loss; b.
Thermal noise that varies with path loss. This generally refers to the basic noise related to path loss and the intermodulation noise related to the baseband noise load level. The basic noise a+b is measured under noise-free load conditions as described in 4.4 below. The total noise a+b+c is measured under noise-added load conditions as described in 4.22
GB/T4958.12-1988
or 4.3 below. 3 Measurement Equipment
3.1 General Considerations
Equipment for measuring noise load performance is commercially available, generally referred to as "white noise testers" or "noise load testers". White noise testers consist of a noise generator and a noise receiver, and a typical circuit connection diagram is shown in Figure 1. In order to ensure the consistency of test equipment and obtain good measurement accuracy, CCIR (Appendix BB.2) and CCITT (Appendix BB.3) have detailed provisions for the characteristics of white noise testers. For measurements of simulated radio relay systems, universal white noise testers are generally accurate enough without considering the errors of the test equipment. However, when the required measurement accuracy is close to the inherent accuracy of the test equipment, the measurement error should be deducted from the presentation of the results. The measurement accuracy depends on many factors, including the following: a. The accuracy of the attenuators and monitors of the signal generator and receiver; b. The number of inserted bandstop filters and the effective bandwidth of the noise measurement channel; c. The area of ​​the load curve used when making the measurement (i.e., the basic noise is the main component or the intermodulation noise is the main component); the order of the main distortion components in the system under test. d.
These factors are discussed in Appendix BB.3 and B.4. 3.2 Noise Generator
3.2.1 Output Characteristics
The RMS value of the noise source voltage shall not vary by more than ±0.001 when measured in a bandwidth of approximately 2 kHz over the frequency range corresponding to the baseband of the system under test.5dB.
The test signal should be a Gaussian amplitude distribution with a minimum peak-to-root-mean-square ratio of 12dB. In order to achieve a load level at least 10dB greater than the conventional load level used, the maximum value of the noise power density output by the noise generator should not be less than -40dBm/kHz. The transmit level should be adjustable to the specified value continuously or in small steps (e.g. 0.1dB) using the output attenuator. The commonly used attenuator range should be greater than 50dB. 3.2.2 Band-limiting and band-stop filters
Use high-pass and low-pass filters to limit the baseband frequency to a range suitable for the simulated system under test, and use a series of band-stop filters to determine the noise measurement channel. The general white noise tester has many filters available, so it can test various commonly encountered channel capacities. Table 2 lists the recommended filter frequencies. Detailed filter specifications are given in Appendix BB.2. 3.2.3 Band-stop filter insertion loss
The noise generator needs to have a wideband noise power output indicator, and a power monitor is usually installed at the end of the filter chain (see Figure 1. The passband attenuation of a crystal band-stop filter is usually a function of frequency, so an equalizer is often connected to compensate for the change in this attenuation. After connecting the equalizer, the total passband insertion loss is on the order of several decibels. After connecting the band-stop filter, the output level should be restored to the initial value to compensate for this insertion loss. New noise generators are equipped with automatic level controllers to automatically correct this error. However, some noise generators have broadband power monitors installed before the band-stop filter. For such instruments, it is necessary to refer to the insertion loss table given in the instrument manual to calibrate the output level. Note: Restoring the output power will change the signal power density, but the frequency band eliminated by the band-stop filter is generally very narrow, and its impact can be 3.3 Noise receiver
Table 2 Recommended filter frequency
Telephone channel occupancy
System capacity
Number of voice channels
Frequency band limit
60-300
Band-limited filter
Effective cutoff frequency
300±2
Universal measurement channel frequency
System capacity
Number of voice channels
Phone channel occupation
Frequency band limit
60-552
(60-1300
164-1296
[60-2540
{64-2660
(60-4028
64-4024
316-4188
60-5636| |tt||（64-5564
316-5564
312-8120
3312-8204
（316—8204||t t||（312-12336
316-12388
312-12388
GB/T4958.12—1988
band limited filtering The
effective cutoff frequency of the device
316±5
316±5
316±5
316±5
552±4||tt| |1296±8
2600±20
4100±30
4100±30
5600±50
5.600±50|| tt||8160±75
12360±10
Universal measurement channel frequency
70270534
702705341248
7027053412482438
7027053412482438
53412482438
7027053412 482438
38865340
53412482438
38865340
53412482438
38865340
53412482438
38865340
76001170
Two different types of noise receivers are usually used. The first type is suitable for measuring the noise power ratio. It is equipped with only an attenuator with a large attenuation range (for example, 0 to 80 dB), which is directly connected to the receiver input (see 4.2). The second type is suitable for measuring the noise power relative to the zero relative level point of the system. Use pWOp or dBmOp as the unit. Such receivers are generally fitted with two attenuators, the first being calibrated in transmission level (dBr) and the second being attenuated in steps of 10 dB and giving a reading with a connected meter (see 4.3). In either case, the design of the amplifiers, mixers and attenuators should be chosen so as to avoid saturation or excessive nonlinear effects at relative levels up to -15 dB when the applied white noise load level exceeds the nominal load level by 10 dB. For a 960-channel system this corresponds to a receiver input level of about +10 dBm. In order to be able to measure the noise power of large capacity systems, the inherent noise of the receiver should be less than -125 dBm at an applied load 10 dB below the nominal load level. The effective bandwidth of the receiver should not be narrower than 1.7 kHz. In order for it to be narrower than the bandwidth of the band-pass filter at 70 dB, it should not be wider than about +2.5 kHz. The centre frequency of the band-pass filter used should coincide with the centre frequency of the band-pass filter of the noise generator. The selectivity of these filters should be high enough to prevent overloading of the receiver's amplifiers or mixers or generating spurious responses. 3.4 Intrinsic intermodulation of white noise tester
GB/T4958.12—1988
Connect the noise generator directly to the noise receiver and make the output noise power level of the noise generator equal to the conventional load (see Table 1). The total noise presented in any noise measurement channel should be equivalent to a noise power ratio of 67dB at a minimum. This is equivalent to a noise power of 85.9dBmOp.
4 Measurement method
4.1 Input noise level
The noise generator is connected to the baseband input of the simulated radio relay system. Select appropriate high-pass and low-pass filters to limit the noise bandwidth to the baseband bandwidth of the system under test. Calculate the conventional load level by formula (1) or (2), or find it in the third column of Table 1. The nominal power level at point R' can be obtained by adding the relative power at point R' to the normal load level, or by looking it up in the fourth column of Table 1. For a certain system capacity (e.g. 1800 channels), when the baseband input is a 37 dBr relative level point, the noise generator output level (Lo) will be: Lot = -15 + 10lg (1800) (dBm0) -37dBr = -19.5dBm
4.2 Noise receiver with noise power ratio as the indication unit (3)
The noise generator and the noise receiver are connected to the baseband input and output of the simulated radio relay system respectively. A noise measurement channel is selected. The band stop filter of the noise generator is not connected to the circuit, and the system input noise level is adjusted to the normal load level or other specified level value. Adjust the receiver attenuator to give a reference reading on the receiver's indicator meter, then connect the appropriate band stop filter to the circuit, and if necessary, readjust the generator level to the original value (see 3.2.3). Reduce the receiver attenuator until the original reference reading is read. The difference between the two readings of the receiver attenuator is the measured noise power ratio. Conversions between noise power ratio and other noise load units are described in Appendix A. 4.3 Noise receiver with noise power or signal-to-noise ratio as the indication unit The noise generator and noise receiver are connected to the input and output of the simulated radio relay system baseband respectively. Select the noise measurement channel and connect the corresponding band-stop filter. The system input noise level is adjusted to the normal level or other specified level value. If necessary, the insertion loss of the filter should be deducted (see 3.2.3).
Adjust the transmission level attenuator of the receiver to a value equivalent to the relative level of the system baseband output. Then adjust the range attenuator to increase the sensitivity until a reading is read on the receiver indicator; if possible, this reading should be within 10dB of the top of the indicator scale. The sum of the range attenuator and the reading on the meter directly gives the noise level relative to the zero relative level point of the system. 4.4 Basic noise
The value measured when no noise load is applied is the basic noise. New noise generators have a noise (on/off) switch that makes this measurement very convenient. This is because it can keep the generator output impedance unchanged when no noise output is generated. Receivers that are calibrated in noise power or level can directly measure the basic noise. Receivers that are calibrated in noise power ratio need to measure the value relative to the reference level. As described in 4.2. The measured noise power ratio can be expressed as a basic noise power ratio, or it can be converted into noise power level units by referring to Appendix A. 4.5 Basic noise related to and independent of path loss The path loss-related component of the basic noise is measured using the method of 4.4, while the path loss-independent component can be measured by simultaneously reducing the path loss of all RF relay segments until the basic noise does not decrease further. This residual noise is the path-independent component of the basic noise.
Note: ① If the received RF carrier level is not increased enough to achieve this condition, extrapolation can usually be used. ② When the received RF carrier level is low, the noise component that is not related to the path loss can be smaller than the measured residual basic noise value. For example, this may be due to the effect of automatic gain control.
The measured basic noise can be plotted as a curve relative to the received RF carrier level (as shown in Figure 2). The basic noise related to the path can be derived from this curve.
GB/T4958.12—1988
4.6 Total noise as a function of noise load level and received RF carrier level According to the method of 4.2 (measuring noise power ratio) or 4.3 (measuring noise power level or signal-to-noise ratio), within the noise load level range relative to the normal load level (for example, -10 to +6 dB), measure the total noise and draw a curve as shown in Figure 3 or Figure 4 (depending on the selected noise measurement unit).
When the white noise load is increased to a value greater than the nominal or normal value, the curve approaches the intermodulation noise that is highly dependent on the load. When the white noise load is reduced to a value less than the normal value, the noise approaches the basic noise that is independent of the load. Generally, the received RF carrier level is adjusted to the nominal value for this measurement. However, because the noise load performance is related to this voltage, the noise load performance is not related to this voltage. There is a strict dependence on the level. The noise load measurement is generally repeated at a lower RF level when simulating the fading of one or more relay segments. For each received RF carrier level, a curve of the total noise change within the noise load level range can be drawn, which can produce multiple curves similar to those shown in Figure 3 or Figure 4. In addition, a curve of the total noise relative to the received RF carrier level change under normal load conditions can be drawn as shown in Figure 2. The noise load performance in the fading state can be measured by changing the path loss of a selected relay segment (all other RF receiver input levels remain unchanged), and a curve of the total noise power relative to the path loss of this relay segment under normal load can be drawn. 5 Representation of results
When the measurement only needs to be performed on a small number of received RF carrier levels When the measurement is carried out under the conditions of received RF carrier and/or load level, the measurement results shall be presented in a table showing the received RF carrier level. Noise measurement channel frequency, etc., as well as the measured basic noise and total noise values. When it is necessary to measure over the entire range of received RF carrier and/or load level, the measured values ​​shall be presented in a curve graph. As shown in Figure 2, Figure 3 or Figure 4.
6 Details to be specified
The following items shall be included in the detailed equipment specification when necessary: ​​a.
Baseband channel capacity;
Frequency of high-pass and low-pass filters; kHz
Pre-emphasis and de-emphasis characteristics;
Relative level at baseband input, dBr;
Normal load level, dBmO,
Noise load level range, relative At the normal load level, dB, the root mean square frequency deviation of each voice channel (1mW, 800Hz), kHzh.
Relative level at the baseband output, dBr,
Center frequency of the noise measurement channel, kHz, i.
Number of relay sections of the circuit,
Range of the receiver RF carrier level;
Allowable basic noise level;
Allowable total noise level.
GB/T4958.12—1988
Equipment health equipment
Strengthen, equipment
The above is a
Reading
Schematic diagram of white noise tester
Relay certification
Voice drop line: 00
Formulas can be collected
with the coal of the positive diameter element point!
Received
Figure 2 Example of total noise and basic noise curve of simulated radio relay system 7
GB/T4958.12—1988
[+Value+ i. tdBn
Figure 3 Example of noise performance as a function of load: measuring the noise power ratio HrE
Figure 4 Example of noise performance as a function of load: measuring the noise power level or weighted signal-to-noise ratio GB/T4958.12—1988
Appendix A
Conversion of measured noise power ratio (npr) to noise power level or signal-to-noise ratio (supplement)
The relationship between the noise power ratio (n·Pr), the signal-to-noise ratio (S/N or S/Np) and the noise meter weighted noise power level Lnp is given by the following formula:
Lnp=—(S/N+W)=—(S/N+2.5)=—(S/Np)dBmOpB
=(npr+L-10g(g. 1kHz)-W)dBmopWhere:
(S/N)-signal to noise ratio, unweighted, dB; (S/Np)-signal to noise ratio, noise meter weighted dB; L-white noise load level. dBmo:
B-effective bandwidth of band-limited filter (frequency of high-pass and low-pass filters. kHz see Table 2): w-
101g(1.74kH2
3.1kHz,
indicates the use of noise meter weighting.
The calculation can be simplified by using the following equation: LNP
Where:
-npr+K)dBmOp
(L-101g(3. 1 kHz
-W)dBmOp
The K values ​​of some commonly used system voice channel capacities are listed in the table below Number of channels
K(dBmOp）
When the system voice channel capacity N≥240 channels, formula (A2) can be approximated by the following formula (the error is within ±0.2dB). Lp=(-npr)-18.97dBmOp
When the system voice channel capacity is 123 (Method for measuring noise power level or signal-to-noise ratio, within the range of noise load levels relative to the normal load level (for example, -10 to +6 dB), measure the total noise and draw a curve as shown in Figure 3 or Figure 4 (depending on the noise measurement unit selected).
When the white noise load is increased to a value greater than the nominal or normal value, the curve approaches the intermodulation noise that is highly dependent on the load. When the white noise load is reduced to a value less than the normal value, the noise approaches the basic noise that is independent of the load. This measurement is generally performed by adjusting the received RF carrier level to the nominal value. However, because the noise load performance is strictly dependent on this level, the noise load measurement is generally repeated at a lower RF level when simulating the fading of one or more relay segments. For each received For any RF carrier level, a curve of the total noise variation within the noise load level range can be plotted, which can produce multiple curves similar to those shown in Figures 3 or 4. In addition, a curve of the total noise relative to the received RF carrier level under normal load conditions can be plotted as shown in Figure 2. The noise load performance in the fading state can be measured by changing the path loss of a selected relay segment (all other RF receiver input levels remain unchanged), and a curve of the total noise power relative to the path loss of this relay segment under normal load can be plotted. 5. Presentation of results
When measurements are only required for a small number of received RF carrier levels and/or load levels, the measurement results should be presented in a tabular form, showing the received Received RF carrier level. Noise measurement channel frequency, etc., as well as the measured basic noise and total noise values. When it is necessary to measure over the entire range of received RF carrier and/or load levels, the measured values ​​should be presented in a curve graph. As shown in Figure 2, Figure 3 or Figure 4.
6 Details to be specified
The following items should be included in the detailed equipment specification when necessary: ​​a.
Baseband channel capacity;
Frequency of high-pass and low-pass filters; kHzwwW.bzxz.Net
Pre-emphasis and de-emphasis characteristics;
Relative level at the baseband input, dBr;
Normal load level, dBmO,
Noise load level range, relative to the normal load level, dB per voice channel (1m W, 800Hz) root mean square frequency deviation, kHzh.
Relative level at baseband output, dBr,
Center frequency of noise measurement channel, kHz, i.
Number of relay sections of circuit,
Range of receiver RF carrier level;
Allowable basic noise level;
Allowable total noise level.
GB/T4958.12—1988
Equipment and health equipment
Strengthening, equipment
The above is a
Reading
Schematic diagram of white noise tester
Relay certification
Call line: 00
Formulas can be collected
with the coal of the positive diameter element!
Received
Figure 2 Example of total noise and basic noise curve of simulated radio relay system 7
GB/T4958.12—1988
[+Value+ i. tdBn
Figure 3 Example of noise performance as a function of load: measuring the noise power ratio HrE
Figure 4 Example of noise performance as a function of load: measuring the noise power level or weighted signal-to-noise ratio GB/T4958.12—1988
Appendix A
Conversion of measured noise power ratio (npr) to noise power level or signal-to-noise ratio (supplement)
The relationship between the noise power ratio (n·Pr), the signal-to-noise ratio (S/N or S/Np) and the noise meter weighted noise power level Lnp is given by the following formula:
Lnp=—(S/N+W)=—(S/N+2.5)=—(S/Np)dBmOpB
=(npr+L-10g(g. 1kHz)-W)dBmopWhere:
(S/N)-signal to noise ratio, unweighted, dB; (S/Np)-signal to noise ratio, noise meter weighted dB; L-white noise load level. dBmo:
B-effective bandwidth of band-limited filter (frequency of high-pass and low-pass filters. kHz see Table 2): w-
101g(1.74kH2
3.1kHz,
indicates the use of noise meter weighting.
The calculation can be simplified by using the following equation: LNP
Where:
-npr+K)dBmOp
(L-101g(3. 1 kHz
-W)dBmOp
The K values ​​of some commonly used system voice channel capacities are listed in the table below Number of channels
K(dBmOp）
When the system voice channel capacity N≥240 channels, formula (A2) can be approximated by the following formula (the error is within ±0.2dB). Lp=(-npr)-18.97dBmOp
When the system voice channel capacity is 123 (Method for measuring noise power level or signal-to-noise ratio, within the range of noise load levels relative to the normal load level (for example, -10 to +6 dB), measure the total noise and draw a curve as shown in Figure 3 or Figure 4 (depending on the noise measurement unit selected).
When the white noise load is increased to a value greater than the nominal or normal value, the curve approaches the intermodulation noise that is highly dependent on the load. When the white noise load is reduced to a value less than the normal value, the noise approaches the basic noise that is independent of the load. This measurement is generally performed by adjusting the received RF carrier level to the nominal value. However, because the noise load performance is strictly dependent on this level, the noise load measurement is generally repeated at a lower RF level when simulating the fading of one or more relay segments. For each received For any RF carrier level, a curve of the total noise variation within the noise load level range can be plotted, which can produce multiple curves similar to those shown in Figures 3 or 4. In addition, a curve of the total noise relative to the received RF carrier level under normal load conditions can be plotted as shown in Figure 2. The noise load performance in the fading state can be measured by changing the path loss of a selected relay segment (all other RF receiver input levels remain unchanged), and a curve of the total noise power relative to the path loss of this relay segment under normal load can be plotted. 5. Presentation of results
When measurements are only required for a small number of received RF carrier levels and/or load levels, the measurement results should be presented in a tabular form, showing the received Received RF carrier level. Noise measurement channel frequency, etc., as well as the measured basic noise and total noise values. When it is necessary to measure over the entire range of received RF carrier and/or load levels, the measured values ​​should be presented in a curve graph. As shown in Figure 2, Figure 3 or Figure 4.
6 Details to be specified
The following items should be included in the detailed equipment specification when necessary: ​​a.
Baseband channel capacity;
Frequency of high-pass and low-pass filters; kHz
Pre-emphasis and de-emphasis characteristics;
Relative level at the baseband input, dBr;
Normal load level, dBmO,
Noise load level range, relative to the normal load level, dB per voice channel (1m W, 800Hz) root mean square frequency deviation, kHzh.
Relative level at baseband output, dBr,
Center frequency of noise measurement channel, kHz, i.
Number of relay sections of circuit,
Range of receiver RF carrier level;
Allowable basic noise level;
Allowable total noise level.
GB/T4958.12—1988
Equipment and health equipment
Strengthening, equipment
The above is a
Reading
Schematic diagram of white noise tester
Relay certification
Call line: 00
Formulas can be collected
with the coal of the positive diameter element!
Received
Figure 2 Example of total noise and basic noise curve of simulated radio relay system 7
GB/T4958.12—1988
[+Value+ i. tdBn
Figure 3 Example of noise performance as a function of load: measuring the noise power ratio HrE
Figure 4 Example of noise performance as a function of load: measuring the noise power level or weighted signal-to-noise ratio GB/T4958.12—1988
Appendix A
Conversion of measured noise power ratio (npr) to noise power level or signal-to-noise ratio (supplement)
The relationship between the noise power ratio (n·Pr), the signal-to-noise ratio (S/N or S/Np) and the noise meter weighted noise power level Lnp is given by the following formula:
Lnp=—(S/N+W)=—(S/N+2.5)=—(S/Np)dBmOpB
=(npr+L-10g(g. 1kHz)-W)dBmopWhere:
(S/N)-signal to noise ratio, unweighted, dB; (S/Np)-signal to noise ratio, noise meter weighted dB; L-white noise load level. dBmo:
B-effective bandwidth of band-limited filter (frequency of high-pass and low-pass filters. kHz see Table 2): w-
101g(1.74kH2
3.1kHz,
indicates the use of noise meter weighting.
The calculation can be simplified by using the following equation: LNP
Where:
-npr+K)dBmOp
(L-101g(3. 1 kHz
-W)dBmOp
The K values ​​of some commonly used system voice channel capacities are listed in the table below Number of channels
K(dBmOp）
When the system voice channel capacity N≥240 channels, formula (A2) can be approximated by the following formula (the error is within ±0.2dB). Lp=(-npr)-18.97dBmOp
When the system voice channel capacity is 121kHz,
indicates the use of noise meter weighting.
The calculation can be simplified by using the following equation: LNP
Where:
-npr+K)dBmOp
(L-101g(3. 1 kHz
-W)dBmOp
The K values ​​of some commonly used system voice channel capacities are listed in the following table Number of voice channels
K(dBmOp）
When the system voice channel capacity N≥240 channels, formula (A2) can be approximated by the following formula (the error is within ±0.2dB). Lp=(-npr)-18.97dBmOp
When the system voice channel capacity is 121kHz,
indicates the use of noise meter weighting.
The calculation can be simplified by using the following equation: LNP
Where:
-npr+K)dBmOp
(L-101g(3. 1 kHz
-W)dBmOp
The K values ​​of some commonly used system voice channel capacities are listed in the following table Number of voice channels
K(dBmOp）
When the system voice channel capacity N≥240 channels, formula (A2) can be approximated by the following formula (the error is within ±0.2dB). Lp=(-npr)-18.97dBmOp
When the system voice channel capacity is 12
Tip: This standard content only shows part of the intercepted content of the complete standard. If you need the complete standard, please go to the top to download the complete standard document for free.