GB/T 4958.14-1992 Methods of measurement for equipment used in terrestrial radio-relay systems Part 1: Measurements common to subsystems and other radio-relay systems Section 2: Measurements of radio frequency range
Some standard content:
National Standard of the People's Republic of China
GB/T4958.14—1992
eqvIEc487-1-2:1984
Methods of measurement for eguipmentused in terrestrial radio-relay systemsPart 1:Measurements common to sub-systemsand simulated radio-relay systemsSection 2:Measurements in the radio-frequency range range
Issued 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 systems Part 1: Measurements common to sub-systems and simulated radio-relay systems Section 2. Measurements in the radio frequency range range
This standard is GB/T4958.14-1992 of the series of standards for "Measurement methods for equipment used in ground radio-relay systems"
This standard is equivalent to the international standard IEC487-1-2 (1984) "Measurement methods for equipment used in ground radio-relay systems Part 1: Measurements common to subsystems and simulated radio-relay systems Section 2: Measurement of radio frequency range". 1 Subject content and scope of application
This standard specifies the basic measurement methods for the radio frequency range of subsystems and simulated radio-relay systems in ground radio-relay systems.
This standard is applicable to the measurement of the following parameters: carrier frequency;
impedance;
-level;
amplitude/frequency characteristics;
group delay/frequency characteristics;
-differential gain and differential phase characteristics:
parasitic signals (including harmonics).
2 Reference standards
GB6662 Measurement methods for equipment used in terrestrial radio-relay systems Part 1: Measurements common to subsystems and simulation systems Section 3: Measurements in the intermediate frequency range
GB/T4958.15 Measurement methods for equipment used in terrestrial radio-relay systems Part 1: Measurements common to subsystems and simulation radio-relay systems Section 4 Measurements in the baseband range GB4958.5 Measurement methods for equipment used in terrestrial radio-relay systems Part 2: Measurements of subsystems Section 4 Frequency modulators||tt ||GB4958.6 Measurement methods for equipment used in terrestrial radio-relay systems Part 2: Measurement of subsystems Section 5 Frequency demodulator Approved by the State Administration of Technical Supervision on October 6, 1992 and implemented on May 1, 1993
3 General
GB/T4958.14—1992
For the various measurements described below, it is not possible to fully describe in advance what should be paid attention to in order to obtain quantitative measurement results with acceptable accuracy in all cases. Therefore, only some common concerns are discussed below. At the ports where the measurement signal is used, the presence of parasitic signals (including harmonics) should not be ignored. These parasitic signals may interfere with the use of the measurement equipment itself or interfere with the simulation system and the subsystem under test. Unwanted signals at the measurement ports should be removed. Although their amplitude may not be sufficient to affect the measurement equipment, they may change the RF characteristics of the measurement (for example, due to heat generation). Mechanical fixings or the position of RF shielding of components, including ferrite isolators and circulators, should not be changed unless there is reason to believe that the overall performance after the change is fully representative of the performance of the simulated system or subsystem under test. In the following chapters, some methods required to protect the measurement equipment from possible RF interference will not be mentioned. When performing swept-frequency measurements, the passband of the test receiver (frequency-selective amplifier, amplitude detector, and oscilloscope) is approximately 50 to 100 times the sweep repetition frequency (related to the waveform of the swept-frequency signal).
The task of directing the measurement is to arrange the measurement equipment as needed so that the measurement errors are kept within the permissible limits. When presenting the measurement results described in the following chapters, it is advisable to use a block diagram of the actual measurement used (showing the load, isolators, low-pass filters, and other components), list the types of various instruments used and the rated power of the attenuators, and state the measurement accuracy and the source of error. If there are any ambiguities, they should be explained.
4 Carrier frequency (carrier frequency)
4.1 Definition and general considerations
Carrier frequency is the frequency in the spectrum of the RF signal that can be modulated with the information signal. Usually the carrier frequency is measured without modulation. If energy spreading is used, the carrier frequency measurement result is invalid. Note: Carrier frequency is represented by f or f in CCIR's recommendations on RF channel configuration. In simulation systems, the carrier frequency can be measured at the output of the end station transmitter or at the output of the relay station transmitter after transmission through multiple heterodyne relay stations. The latter will have different values due to the number of frequency changes and the frequency error of the local oscillator. 4.2 Measurement method
The general block diagram for measuring the unmodulated carrier frequency is shown in Figure 1. If there are spurious signals, a bandpass filter needs to be added. If the level range of the frequency meter is smaller than the level range required for the measurement, an attenuator needs to be added. Before making any measurements, the device under test and the measuring equipment itself should be thermally stable. Figure 1 Block diagram for measuring the frequency of an unmodulated RF carrier 1—Device under test; 2—Bandpass filter (if necessary); 3—Attenuator; 4—Digital frequency meter 5—Recorder (optional) The reading of the digital frequency meter is related to its accumulation time and is read within a certain time interval, such as 1 s. The recorder can be used to record a series of readings of the digital frequency meter. In practice, nearly 100 readings are sufficient. This number depends on whether noise exists and whether the noise modulates the signal or is superimposed on it. Usually, a statistical series analysis averaged over several measurement intervals proves that the measurement results are repeatable. Note: The above method can also be applied when the RF carrier is modulated by a baseband signal as long as the digital frequency meter does not introduce errors related to the frequency and frequency deviation of the modulating signal. The averaging interval of the digital frequency meter should exceed 100 cycles of the modulation frequency. 4.3 Expression of measurement results
The readings of the digital frequency meter shall be recorded manually or automatically as a function of time. The accumulation time of the digital frequency meter shall be stated.
4.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: a. Carrier frequency;
Tolerance.
5 Measurement of impedance
5.1 Definitions and general considerations
The input or output impedance of equipment used in radio-relay systems is usually expressed in terms of return loss or voltage standing wave ratio relative to the nominal impedance value of the equipment under test.
The return loss L of an impedance Z relative to its nominal impedance value Zo is given by the following formula: L-201g
or as
where p is the voltage reflection coefficient of the impedance Z relative to Zo, that is, the relationship between the return loss (L) and the voltage standing wave ratio (VSWR) is as follows Z
z+z.
(dB）·Www.bzxZ.net
VSWR+1)
L=201gVSWR-i
5.2 Measurement method
The following measurement method is only applicable to measuring the return loss or voltage standing wave ratio of linear devices. When measuring nonlinear devices or when there is an external signal, some special methods are required, which are not given here. The measurement can be carried out by point-by-point method or sweep frequency method. The point-by-point method requires a large number of measurements and thus wastes a lot of time. Either method can be applied to the measurement line or reflectometer technology. The voltage standing wave ratio can be measured with the best technical equipment with an accuracy of less than 0.01. 5.2.1 Measurement line point-by-point method
The typical measurement block diagram of the measurement line point-by-point method is shown in Figure 2. The device under test is linear to the RF signal level required to be used on the voltage standing wave ratio indicator. The signal generator is usually amplitude modulated. The movable probe includes an adjustable or a broadband diode detector. The voltage standing wave ratio indicator is usually a frequency-selective amplifier tuned to the modulation frequency (for example, 1 to 200 kHz). The measurement should be performed on all required RF bands.
5.2.2 Measuring line sweep frequency method
GB/T4958.14—1992
Figure 2 Typical block diagram of measuring voltage standing wave ratio using measuring line point-by-point method 1-modulated RF signal generator; 2-low-pass filter 3-RF attenuator, 4-measuring line with movable probe and detector, 5-equipment under test; 6-voltage standing wave ratio indicator
The typical measurement block diagram of the measuring line sweep frequency method is shown in Figure 3. The swept frequency signal generator is amplitude modulated, the movable probe has a broadband diode detector, and there is a detector at the output end of the frequency selective amplifier and is tuned to the modulation frequency. The voltage standing wave ratio indicator can be an oscilloscope (storage type is better) or an XY recorder. The measuring equipment can be calibrated with a load of known mismatch value. The horizontal scan of the oscilloscope corresponds to the frequency scan of the swept frequency signal generator. When measuring at the lowest end of the RF, the detector must move at least half a wavelength, and the frequency scan should include all required RF frequency bands.
At any given RF frequency (corresponding to a given point on the horizontal axis), the ratio of the maximum and minimum amplitudes of the envelope marked by the calibration line is the voltage standing wave ratio at that frequency. 【m·
Figure 3 Typical block diagram of measuring voltage standing wave ratio by measuring line sweep frequency method 1-modulated sweep frequency signal generator, 2-low pass filter and directional coupler, 3-RF attenuator; 4-measuring line with moving probe and detector 5-tested equipment; 6-calibrated storage oscilloscope; 7-frequency selective amplifier and detector, 8-automatic level control detector 5.2.3 Reflectometer sweep frequency method
The typical measurement block diagram of the reflectometer sweep frequency method is shown in Figure 4. The sampling of incident power and reflected power can be obtained by a four-terminal directional network. From these incident power and reflected power samples, the modulus of the reflection coefficient at each frequency can be measured. To calibrate the measuring equipment, the device under test can be replaced by a short-circuit and the attenuator can be used to simulate a known return loss. For example, a 26 dB attenuation corresponds to a 26 dB return loss. This calibration method is better than the method that requires knowing the detector law. If the incident wave level is not constant, the calibration line will not be horizontal. The calibration curve is recorded and written in "Representation of measurement results" 4
GB/T4958.14-1992
. By adjusting the gain of the oscilloscope, the change of return loss in the entire swept frequency band can be easily measured. Note: 1) The directivity of the directional network exceeds the range of the measured return loss. The obtainable accuracy is determined. For example, with a directivity of 40 dB, when measuring a 26 dB return loss, the obtainable accuracy is limited to 2 dB. 2) A reflectometer capable of making amplitude and phase measurements can be used to display the measurement results on a Smith chart. Huahua
(optional)
Assume the training is based on
Figure 4 Typical block diagram of return loss measurement using a reflectometer 1-sweeper 2-RF isolator, 3-low-pass filter, 4-4-terminal directional coupler (reflectometer); 5-test device; 6-oscilloscope; 7-detector; 8-variable RF attenuator; detector and filter
5.3 Representation of measurement results
The measurement results should be represented by a curve or photo displayed on the oscilloscope with a calibration line, or copied as an XY curve. When the measurement results are not represented graphically, they should be given as follows: "The return loss in the frequency range of 6.1 to 6.2 GHz is greater than 26 dB." In other words, the voltage standing wave ratio should be given over the entire required frequency range. The maximum error of the measurement result should be given.
5.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: a. nominal impedance;
minimum return loss or maximum voltage standing wave ratio allowed; b.
frequency range.
6 Level measurement
6.1 Definitions and general considerations
In the radio frequency range used by terrestrial radio-relay systems, the term "level" usually refers to power. The purpose of this clause is to define level, power gain, insertion gain (or loss) and isolation. 6.1.1 Input level
The input level is defined as the power delivered to the device under test by a signal generator having an output impedance that matches the nominal input impedance Z of the device under test.
GB/T4958.14—1992
Note: If the device under test and the signal generator are not matched, the power delivered is not the maximum value. 6.1.2 Output Level
The output level is defined as the power delivered by the device under test to a load that matches the nominal transmission line characteristic impedance at the device output port. 6.1.3 Power Gain
The power gain of a device or subsystem is defined as the ratio of the output level to the input level, expressed in decibels. If the device under test is nonlinear, the power gain should be specified, such as "saturation power gain" or "small signal power gain". If the power gain expressed in decibels is a negative value, the sign is usually changed and the value is taken as loss. 6.1.4 Insertion Gain
The insertion gain of a device or subsystem is defined as the ratio of the actual power absorbed by the load in the following two cases: a. The power absorbed when the load is directly connected to the power source P1 b. The power absorbed when the same load is connected to the same power source through the device under test P2. The insertion gain expressed in decibels is:
If the insertion gain expressed in decibels is a negative value, the sign is usually changed and the value is taken as loss. 6.1.5 Isolation (between two ports of a device) (4)
The isolation between two ports of a device is defined as the ratio of the incident wave level on one port to the level of the wave on the other port when all ports are connected to the nominal impedance, expressed in decibels. 6.2 Measurement method
Power levels can be measured using a power meter. The impedance of the RF power meter probe is close to their nominal impedance. RF power meters are very suitable for measuring the available power at the measured port. Power meters can be used to measure powers from less than 1μW to several watts. If larger powers are measured, precision attenuators or calibrated directional couplers with appropriate power ratios can be used to extend the range. When higher sensitivity is required or there are parasitic signals at the measurement end, other methods can be used, such as frequency-selective level meters or appropriately calibrated spectrum analyzers.
Note: When the measured signal undergoes mode conversion through the waveguide, i.e. part of the power is converted to a mode other than the fundamental mode, a mode converter is required to ensure that the full power of the RF signal can be measured. However, the fundamental mode power received is usually sufficient. 6.2.1 Input Level
The input measurement signal level should be measured by connecting a terminal load with a nominal impedance Z in parallel to the output of the signal generator. The level is then measured when the output of the signal generator is connected to the input of the device under test without further adjustment. The return loss corresponding to the terminal load with nominal impedance Z should be greater than 30 dB.
Note: Some of the previous procedures may not be necessary for modern instruments, as these instruments are usually calibrated using an electromotive force or potential difference connected in parallel to a matching load.
6.2.2 Output level
6.2.2.1 Low level test
A sensitive and selective receiver with a carrier level meter is connected to the port under test through a matching variable attenuator. In order to ensure that the receiver is not saturated, it should be noted that when the attenuator is reduced, the meter reading changes proportionally to the input level of the signal. Then adjust the attenuator to a suitable reading and record the reading. The device under test is replaced by a signal generator with a known output power. The signal generator and the receiver are adjusted to the same frequency, and a calibrated precision variable attenuator (which can be placed inside or outside the signal generator) is adjusted to the same as the meter reading recorded previously. The output power of the signal generator. Taking into account the attenuation of the attenuator, it will be equal to the output power of the port of the device under test. A spectrum analyzer can also be used instead of the receiver. 6
6.2.2.2 High level measurement
GB/T4958.14—1992
Connect a calibrated directional coupler between the port to be measured and the matched load. Connect a power meter to the measuring arm of the directional coupler to measure the power. If necessary, connect a calibrated attenuator and a suitable filter (to remove parasitics, harmonics or other unwanted carriers) between the power meter and the measuring arm of the directional coupler. The reading should take into account the total insertion loss of the directional coupler and attenuator. 6.2.3 Gain, loss and isolation measurements
Gain, loss and isolation can all be measured using a suitable level meter. Isolation is measured by applying a signal to the appropriate port and then measuring the signal level at the other port. All other ports should be terminated with nominal impedance during the measurement. Any unwanted signal levels should be small enough to be ignored. A typical block diagram for measuring insertion gain or loss as a function of frequency is shown in Figure 5. The display device can be an XY recorder or a dual-trace oscilloscope. The scanning voltage is sent to the X-amplifier of the display device. When using an XY recorder, the scanning rate should be consistent with its conversion rate. The RF signal at the output end of the sweep signal generator is amplitude modulated with a low-frequency signal (for example 1kHz) and scanned simultaneously over the entire given frequency range.
Figure 5 Typical block diagram for measuring RF insertion gain and loss 1-Modulated swept frequency signal generator; 2-RF isolator; 3-Input directional coupler; 4-Device under test; 5-Output directional coupler; 6-RF load; 7-XY recorder, 8-Monitor detector; 9-Low-pass filter; 10-Oscilloscope (optional); 11-Precision RF variable attenuator; 12-RF detector; 13-Low-frequency logarithmic amplifier and detector The output of the RF detector is a low-frequency signal, which is amplified and detected by a low-frequency logarithmic amplifier-detector (the logarithmic amplifier is used to conveniently display large insertion loss changes): the amplitude of the low-frequency signal is related to the RF signal on the RF detector, and therefore to the insertion gain (or loss). The detected low-frequency input signal is sent to the Y-amplifier of the recorder or the Y-input of the oscilloscope. Another detector can be used to monitor the RF input level to the device under test. This detector can also be used to automatically control the output level of the swept signal generator, and the other Y-input of the oscilloscope can be used to verify that the input signal to the device under test remains unchanged. Note: An XY recorder can also be used to verify that the input level to the device under test remains unchanged, as long as the input of the low-frequency logarithmic amplifier-detector is connected to the output of the monitor-detector.
Before measuring, connect the output directional coupler directly to the input directional coupler, such as connecting points A and B in Figure 5, place the swept signal generator at the required fixed frequencies, and use precision variable attenuators to perform level corrections on the required various values (such as 0.1dB, 0.2dB, 0.3dB or 1dB, 2dB, etc.) at these frequencies. 7
GB/T4958.14—1992
Then connect the device under test between points A and B, set the attenuator to the lowest value in the calibration process, and express the insertion gain (or loss) of the device under test against the frequency. In the measurement block diagram of Figure 5, a directional coupler is used to measure the output power. For the measurement of low output power insertion gain or insertion loss, the directional coupler and matching load can be replaced by a one-way device, which connects the device under test to the RF variable attenuator.
Measurement of insertion gain (or loss) or return loss (modulus and angle) by swept frequency method is more suitable with a combined instrument which uses a linear mixer with wide dynamic range (e.g. 70 dB) to heterodyne two signals (input and output for insertion gain or loss, incident and reflected for return loss) to a low intermediate frequency, e.g. 20 kHz. Such a mixer has a uniform frequency response in the frequency range of about 10 MHz to 12 GHz. Using such a measuring device, it is possible to obtain an accuracy of 0.1 dB/10 dB over a wide range (e.g. 70 dB) when measuring gain or loss, and an accuracy of 0.02 dB over any 3 dB range when measuring broadband frequency response. The measurement results can be displayed with an XY recorder or oscilloscope.
6.2.4 Expression of measurement results
Gain, loss or level at a given frequency should be expressed in decibels or, as required, in decibels relative to a certain power. If the RF transmission line used for the measurement is capable of exciting multiple modes, the specified mode or modes used for the measurement results shall be stated.
6.2.5 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: a. Level,
b. Gain or loss,
c. Frequency range.
7 Amplitude/frequency characteristics
7.1 Definitions and general considerations
The amplitude/frequency characteristic is the relationship between the ratio of the output level to a reference level (expressed in decibels) and the frequency, with the input level unchanged. Usually this reference level is the output level at a given frequency. This definition is only used for linear or nearly linear networks and is not applicable to nonlinear networks. 7.2 Measurement method
The measurement is preferably made by the swept frequency method. In the swept frequency method, the output of the swept frequency signal generator is connected to the input of the device under test, and the output of the device under test is sent to a broadband detector or tracking frequency selector with a flat amplitude/frequency characteristic. It can also be measured by the point-by-point method.
7.3 Presentation of measurement results
For swept frequency measurements, a photograph of the display or a copy of the XY curve should be provided. When the measurement is not presented graphically, it should be given as follows:
"The amplitude/frequency characteristic in the frequency range of 6.0 to 6.4 GHz (corresponding to the amplitude at 6.2 GHz) is +0.2 to -0.1 dB".
Point-by-point measurements can be presented in a table or as specified above. When ripple components are easily identifiable in the measured characteristics, their amplitude (dB,,) and their period (MHz) should be stated. 7.4 Details to be specified
In the detailed equipment specification, the following items should be specified, if necessary: the allowable amplitude change;
the allowable amplitude change rate,
frequency range
d. reference frequency.
8 Group delay/frequency characteristics
8.1 Definitions and general considerations
The transfer function of a linear network can be written as: Where: A(o)—amplitude/frequency characteristics;
B(@)—phase/frequency characteristics;
GB/T4958.14—1992
H(jo)=A(@) ·eB(o).
(If the output signal lags behind the input signal, it is considered positive) The group delay (の) of a linear network is defined as the first-order derivative of the phase B() with respect to の, that is, (α)_dB()
expressed in seconds, and this definition is the same for intermediate frequency and radio frequency. The change in group delay is usually measured, that is, the difference between the above group delay and the group delay at the reference frequency. 8.2 Measurement method
(5)
Measurements are made using a frequency modulated RF signal swept over a given frequency range. This signal is usually obtained by frequency conversion similar to an intermediate frequency signal.
In fact, this measurement is made at an intermediate frequency (see Article 6.2 of GB6662). In order to adapt the RF device under test to the frequency range of the intermediate frequency signal generator and receiver, linear broadband up-converters and down-converters are required. Two types of measurements are required, one is to loop the measurement device itself to determine the residual group delay of the measurement device, and the other is to connect the device under test to obtain the total group delay. The group delay of the device under test is equal to the total group delay minus the residual group delay. When the converters are connected to each other by a transmission line, in order to minimize the group delay ripple, the impedance of the RF interface of the up-converter and down-converter should be very close to their nominal values. If this is not taken into account, errors will increase because the equivalent transmission line length of the device under test is not included in the initial calibration.
There should be linearity between the IF and RF ports of the upconverter. In addition, the RF bandpass filter at the RF output port of the upconverter should ensure that only the upper sideband or lower sideband passes through the device under test. The RF bandpass filter itself should have a flat group delay/frequency characteristic, or the group delay characteristic should have a flat frequency response with the help of a suitable equalizer. In some cases, the equalizer can be incorporated into the IF or high frequency part of the device under test. If the device under test is an RF bandpass filter, the filter and equalizer mentioned above can be omitted. Note: The method of vector-voltmeter or network analyzer can be applied. 8.3 Representation of measurement results
The group delay/frequency characteristic is best represented as a graph displayed by an oscilloscope with frequency as the horizontal axis, similar to that shown in Figure 6. 9
GB/T4958.14—1992
Figure 6 Oscilloscope display legend for group delay frequency characteristics When measurement results are not presented graphically, they should be given as follows: "The total delay variation over the frequency range 6.1356.155 GHz is 1.5 ns." When ripple components are easily identifiable in the measured characteristics, their values (nsp) and their periods (MHz) should be stated. 8.4 Details to be specified
In the detailed equipment specification, the following items should be specified, if necessary: a. Required RF bandwidth;
Modulation (measurement) frequency;
c. The permissible group delay variation within the required RF bandwidth;
c. The permissible group delay slope within the required RF bandwidth. d.
9 Differential gain and differential phase characteristics
9.1 Definitions and general considerations
In small capacity radio-relay systems, the measurement of the amplitude/frequency characteristics (see Chapter 7) and the group delay/frequency characteristics (see Chapter 8) between the two ports of the RF subsystem are generally sufficient to evaluate the baseband distortion introduced by the equipment, and the non-linear effects (i.e., amplitude modulation/phase modulation conversion) are usually negligible. However, in radio-relay systems with a capacity approaching or exceeding 900 channels, the non-linear distortion of the FM signal becomes important. Therefore, in addition to measuring the group delay characteristics, it is necessary to measure the differential gain and phase. Note: Systems with less than the above capacity may also require the measurement of differential gain and phase when the carrier spacing used is smaller than the carrier spacing recommended by CCIR. Differential gain (DG) and differential phase (DP) were originally defined for equipment with baseband input and baseband output terminals (see GB/T4958.15, Sections 5.1.1 and 5.2.1). By adding an upconverter to the IF measurement modulator and a downconverter to the IF measurement demodulator, the basic definition of a high-frequency, small-amplitude test signal and a low-frequency, large-amplitude sweep signal being transmitted simultaneously through the device under test can be extended to RF devices. Direct RF measurement modulators can be used to replace the upconverter and IF modulator. These additions should have much smaller DG and DP distortion than the device under test. The definitions of IF measurement modulators and demodulators are given in GB4958.5 and GB4958.6. Upconverters and downconverters for measurement purposes will be discussed in the following clauses. The significance of DG and DP responses, the choice of measurement frequencies, and the calibration of measurement equipment will be discussed in Chapter 7 of GB6662. These considerations also apply to measurements of RF subsystems.
DG measurement usually includes the combined effect of the amplitude modulation and phase modulation conversion of the nonlinear network and the group delay slope of the preceding linear network. For this reason, it should be remembered that the entire DG response cannot be determined from individual DG measurements; therefore, when performing DG and DP measurements on RF subsystems, the full 10
differential gain and phase of the cascaded subsystem (such as a channel filter and an output amplifier) with linear and nonlinear distortion must be measured.
GB/T4958.14—1992
Note: For cascaded linear and nonlinear networks, the mathematical relationship between the measured DG and DP and the network parameters is given in Appendix C of GB6662. These relationships are generally applicable to RF cascade networks. However, when special amplifiers (such as phase-locked loop amplifiers, frequency division and frequency multiplication amplifiers) are cascaded, the measured DG and DP characteristics cannot be directly applied to evaluate the baseband distortion introduced by the device under test. 9.2 Measurement methods
A simplified block diagram for measuring DG and DP in the RF band is shown in Figure 7. The block diagram has a line analyzer suitable for measuring DG and DP in the IF band (see GB6662, Section 7.3). In order to generate the RF measurement signal and convert the output of the RF device under test to an IF to suit the IF receiver of the line analyzer, an RF extension section is added. Two methods for generating the RF measurement signal are shown in Figures 7a and 7b.
In Figure 7a, a broadband upconverter with a tunable local oscillator is used to heterodyne the IF measurement signal to RF. This method is only suitable for measuring RF networks that appear in one sideband of the converter output using a bandpass filter (e.g., a channel filter of a radio receiver). In order to measure broadband RF networks, another arrangement can be used, shown in Figure 7b, where a microwave swept signal generator is used directly to generate the RF measurement signal. The external FM input port is excited with the baseband sweep and measurement signal of the line analyzer. The generator also uses an RF measurement modulator.
Conversion of the RF output of the device under test to an intermediate frequency is accomplished by a downconverter comprising a broadband low level mixer and an adjustable local oscillator. Automatic frequency control circuitry is also used to ensure that the correct intermediate frequency is output to the receiving section of the line analyzer.
Note: To ensure the accuracy of the measurement, the characteristics of the external FM input port of the swept signal generator need to be considered. 9.3 Presentation of measurement results
Differential gain and phase are best presented as a photograph of the oscilloscope display or as XY values with the two axes calibrated accordingly. If possible, both characteristics can be presented on one photograph. Alternatively, the difference in the extremes of the characteristics may be shown together with the appropriate swept frequency range. Whether the measurement method of Figure 7a or Figure 7b is used should be stated. 9.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: Frequency of the measurement signal;
Sweep width:
Maximum allowable differential gain distortion (%) or equivalent curvature distortion (ns2); Maximum allowable differential phase distortion (degrees or radians) or equivalent group delay distortion (ns). 1
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Figure 7a Simplified block diagram of the use of medium-frequency signal and up-converter to obtain RF measurement signal 1—Transmitter part, 2—Up-converter, 3—Equipment under test; 4—Down-converter; 5—Receiver part14—1992
Note: For cascaded linear and nonlinear networks, the mathematical relationships between the measured DG and DP and the network parameters are given in Appendix C of GB6662. These relationships are generally applicable to RF cascade networks. However, when special amplifiers (such as phase-locked loop amplifiers, frequency division and frequency multiplication amplifiers) are cascaded, the measured DG and DP characteristics cannot be directly used to evaluate the baseband distortion introduced by the device under test. 9.2 Measurement methods
A simple block diagram for measuring DG and DP in the RF band is shown in Figure 7. The block diagram has a line analyzer suitable for measuring DG and DP in the intermediate frequency band (see GB6662 Section 7.3). In order to generate the RF measurement signal and convert the output of the RF device under test to an intermediate frequency to suit the intermediate frequency receiver of the line analyzer, an RF extension section is added. Two methods for generating the RF measurement signal are shown in Figures 7a and 7b.
In Figure 7a, a wideband upconverter with a tunable local oscillator is used to heterodyne the IF measurement signal to RF. This approach is only suitable for measuring RF networks that appear in one sideband at the converter output using a bandpass filter (e.g., the channel filter of a radio receiver). To measure wideband RF networks, an alternative arrangement can be used, shown in Figure 7b, where a microwave swept-frequency signal generator is used directly to generate the RF measurement signal. The external FM input port is stimulated with the line analyzer's baseband swept and measurement signal. The generator also uses an RF measurement modulator.
Conversion of the DUT's RF output to IF is accomplished using a downconverter that includes a wideband low-level mixer and a tunable local oscillator. Automatic frequency control circuitry is also used to ensure an accurate IF output to the line analyzer's receiving section.
Note: To ensure measurement accuracy, the characteristics of the external FM input port of the swept-frequency signal generator need to be taken into account. 9.3 Presentation of measurement results
Differential gain and phase are preferably presented as a photograph of an oscilloscope display or as XY values with the two axes calibrated accordingly. If possible, both characteristics may be presented on one photograph. Alternatively, the difference in the extremes of the characteristic may be stated together with the appropriate sweep range. Whether the measurement method of Figure 7a or Figure 7b is used should be stated. 9.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: frequency of the measurement signal;
sweep width;
maximum permissible differential gain distortion (%) or equivalent curvature distortion (ns2); maximum permissible differential phase distortion (degrees or radians) or equivalent group delay distortion (ns). 1
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Figure 7a Simplified block diagram of obtaining RF measurement signal using IF signal and upconverter 1—transmitter part, 2—upconverter, 3—device under test; 4—downconverter; 5—receiver part14—1992
Note: For cascaded linear and nonlinear networks, the mathematical relationships between the measured DG and DP and the network parameters are given in Appendix C of GB6662. These relationships are generally applicable to RF cascade networks. However, when special amplifiers (such as phase-locked loop amplifiers, frequency division and frequency multiplication amplifiers) are cascaded, the measured DG and DP characteristics cannot be directly used to evaluate the baseband distortion introduced by the device under test. 9.2 Measurement methods
A simple block diagram for measuring DG and DP in the RF band is shown in Figure 7. The block diagram has a line analyzer suitable for measuring DG and DP in the intermediate frequency band (see GB6662 Section 7.3). In order to generate the RF measurement signal and convert the output of the RF device under test to an intermediate frequency to suit the intermediate frequency receiver of the line analyzer, an RF extension section is added. Two methods for generating the RF measurement signal are shown in Figures 7a and 7b.
In Figure 7a, a wideband upconverter with a tunable local oscillator is used to heterodyne the IF measurement signal to RF. This approach is only suitable for measuring RF networks that appear in one sideband at the converter output using a bandpass filter (e.g., the channel filter of a radio receiver). To measure wideband RF networks, an alternative arrangement can be used, shown in Figure 7b, where a microwave swept-frequency signal generator is used directly to generate the RF measurement signal. The external FM input port is stimulated with the line analyzer's baseband swept and measurement signal. The generator also uses an RF measurement modulator.
Conversion of the DUT's RF output to IF is accomplished using a downconverter that includes a wideband low-level mixer and a tunable local oscillator. Automatic frequency control circuitry is also used to ensure an accurate IF output to the line analyzer's receiving section.
Note: To ensure measurement accuracy, the characteristics of the external FM input port of the swept-frequency signal generator need to be taken into account. 9.3 Presentation of measurement results
Differential gain and phase are preferably presented as a photograph of an oscilloscope display or as XY values with the two axes calibrated accordingly. If possible, both characteristics may be presented on one photograph. Alternatively, the difference in the extremes of the characteristic may be stated together with the appropriate sweep range. Whether the measurement method of Figure 7a or Figure 7b is used should be stated. 9.4 Details to be specified
In the detailed equipment specification, the following items shall be specified, if necessary: frequency of the measurement signal;
sweep width;
maximum permissible differential gain distortion (%) or equivalent curvature distortion (ns2); maximum permissible differential phase distortion (degrees or radians) or equivalent group delay distortion (ns). 1
Green trap srtita
Figure 7a Simplified block diagram of obtaining RF measurement signal using IF signal and upconverter 1—transmitter part, 2—upconverter, 3—device under test; 4—downconverter; 5—receiver part
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