JPH036047Y2 - - Google Patents

Description

[Detailed description of the invention] The invention applies a frequency signal of a desired wave to the input terminal of a spurious response device, particularly an FM receiver to be measured, and simultaneously applies a swept frequency signal of a frequency-swept interference wave. , relates to a spurious response measurement device that measures the presence or absence of a spurious response from the interference beat component generated at the output end of the FM receiver under test when operated, and quickly and automatically obtains the frequency of the spurious response. .

Spurious response, which produces a certain low frequency output and is expressed as the intensity ratio of the desired signal and the interference signal, is an important measurement item as it indicates the selectivity of the receiver. The noise suppression method (NQ method) is generally used to measure spurious responses, but since it is not possible to predict all frequencies at which spurious responses occur, it is necessary to search over a wide range of frequencies. Also, since it is not known at what level spurious will occur, it is necessary to search for the level as well.

Conventional spurious response measurement devices manually perform frequency sweeps to search over a wide range of frequencies, and the human ear is used to distinguish slight changes in the timbre of low-frequency noise, which can lead to overhearing due to human fatigue. There were problems with accuracy, and it took a long time to search over a wide range of frequencies, and when the speed of the sweep frequency was increased, changes in timbre could not be heard.

This invention aims to solve the above problems, and is a spurious response device that automatically measures the occurrence frequency of spurious responses without relying on human hearing, and speeds up the search speed for a wide range of frequencies. is intended to provide. Therefore, the spurious response device of the present invention has a desired wave signal generator that generates a desired wave frequency signal, a sweep signal generator that generates a swept frequency signal as an interference wave, and a matching system that superimposes the desired wave and the interference wave. A signal in which the desired wave and interference wave are superimposed is applied to the input terminal of the FM receiver under test, and the combined wave of the Z-shaped output and interference beat generated at the output terminal is received, and the level of the combined wave is determined. a variable leveler for adjusting the level; a beat detection section for obtaining a detected waveform of an interference beat from the composite wave whose level has been adjusted by the variable leveler; and a predetermined peak value of the detected waveform detected by the beat detection section. a sawtooth wave generation circuit that supplies a sawtooth wave to a sweep signal generator, and a control section that controls the desired wave signal generator, the sweep signal generator, and the variable level generator. There is. The control unit includes a sweep control means for controlling the sawtooth wave generation circuit to cause the sweep signal generator to generate the sweep frequency signal corresponding to the center frequency and frequency band of the FM receiver to be measured, and When no output signal is output from the comparator in the pre-processing of the level search prior to the level search, the sweep control means is instructed to perform a sweep, and each time the variable level device is controlled to output an output signal from the comparator, the measured level is and the sweep control means that receives a level setting completion signal from the variable level control means controls the sawtooth wave generation circuit to cause the sweep signal generator to sweep, and the comparator controls the output signal. frequency value reading storage means for reading and storing the frequency of the sweep signal generator when outputting the frequency band; and signal generator control means for controlling the sweep signal generator from information stored in the sweep frequency band storage means. , is configured to read the spurious frequency of the FM receiver under test. This will be explained below with reference to the drawings.

Before explaining the present invention, the principle of the swept wave interferometric measurement method (described in Japanese Patent Application Laid-open No. 53-42868) of spurious responses of FM receivers, which is the basis of the present invention, will be explained in Fig. 1. Let's briefly explain using

In Figure 1, 1 is a standard signal generator that generates a desired signal, 2 is a frequency sweep signal generator that generates an interference signal, 3 is a matching device, and 4 is an FM to be measured. In the receiver, 5 is a high-pass filter, 6 is a rectifier, and 7 is a low-pass filter.

When the frequency sweep signal of the interference wave signal from the frequency sweep signal generator 2 passes through the reception band of the FM receiver under test 4 while the desired wave signal of the standard signal generator 1 is cut off, the FM receiver under test The low frequency output of 4 is as shown in Figure 2. This is the so-called measured object.
This is the output waveform of the S-shaped characteristic of the discriminator of the FM receiver 4, but in this case, the waveform is rather close to Z-shaped due to the influence of the intermediate frequency filter.
Hereinafter, this will be referred to as "Z-shaped output." Note that noise is generated at both ends of the Z-shaped output in FIG. 2 because the sweep signal is outside the band. Next, when the standard signal generator I is operated and a desired wave signal whose output is sufficiently larger than the frequency sweep signal of the frequency sweep signal generator 2 is further applied, the output of the FM receiver under test 4 is as shown in FIG. become. This is a composite wave of the interference beat of the desired wave signal and the frequency sweep signal and the Z-shaped output. Further, the noise seen in FIG. 2 is suppressed by applying the desired wave signal and is not seen in FIG. 3.
The above interference beat is generated as a result of the combined phase change of the desired wave signal and the frequency sweep signal being captured as a frequency change by the discriminator of the FM receiver under test 4, and the peak value of this output is the frequency Theoretical and experimental results have shown that this is directly proportional to the sweep signal strength. However, the condition that the desired wave signal strength is greater than the frequency sweep signal strength and constant is required. The above explanation is based on the fact that the frequency of the frequency sweep signal is directly measured.
This is a case where the frequency matches the reception band of the FM receiver 4, but the interference beat generation mechanism is the same at the frequency of the spurious response, and this interference beat is applied to the measurement of the spurious response.

The output of the FM receiver under test 4 enters the high-pass filter 5.
The Z-shaped output of the receiver 4 is removed, and only the interference beats are extracted. Emphasis is applied to restore the high frequencies de-emphasized by the FM receiver 4 under test, and the low frequency of the FM receiver 4 under test is The bandwidth is equivalently expanded. The interference beat output from the high-pass filter 5 is detected by a rectifier 6 to facilitate amplitude measurement, and then detected by a low-pass filter 7.
It is smoothed by passing it through. The output waveform of the interference beat output from the low-pass filter 7 becomes a bimodal pulse as shown in FIG.
This is the case when the frequency is at the center of the reception band (intermediate frequency) of the receiver 4. For example, if the frequency of the desired wave signal of the standard signal generator 1 is located at the edge of the reception band, it becomes a single peak pulse. The peak value of the bimodal pulse or single peak pulse of the interference beat output from the low-pass filter 7 is directly proportional to the frequency sweep signal strength as explained above.
The peak value of the interference beat output from the low-pass filter 7 changes in proportion to the frequency sweep signal strength of the interference wave signal generated from the low-pass filter 7. This characteristic is used to automatically measure the frequency of spurious responses.

FIG. 5 shows the configuration of an embodiment of the spurious response device according to the present invention.

In FIG. 5, 11 is a desired wave signal generator which generates a desired wave frequency signal; 12
13 is a matching device that superimposes the desired wave signal and the interference wave signal; 14 is the FM receiver to be measured, which generates a swept frequency signal of the interference wave; 14 is the FM receiver to be measured; An example of this is a device having a filter, a mixer circuit, and a detection circuit, and 15 is a variable level device that generates a composite wave of the Z-shaped output from the FM receiver 14 under test and the interference beat (hereinafter referred to as composite wave). Something that changes the level of
Reference numeral 16 is a beat detection unit that obtains a detected waveform corresponding to the interference beat component from the composite wave, and 17 is a comparator that detects a predetermined level and the peak value of the detected waveform obtained from the beat detection unit 16. 18 is a counter that counts the sweep frequency of the sweep signal generator 12;
9 is a sawtooth wave generating circuit, which is a sweep signal generator 1;
2, 20 is a control section which includes a sweep frequency band storage means 23, a variable level control means 24, a frequency value reading storage means 25, a calculation means 26, and a signal generator control means, which will be explained below. 27 and sweep control means 28, which are composed of hardware such as a microprocessor, ROM, and RAM, and 21 is an input key for inputting the sweep start frequency, sweep end frequency, and measurement start signal from the outside. Reference numeral 22 represents a display device which is stored in the frequency value reading storage means 25 and displays the frequency of the spurious response. The sweep frequency band storage means 23 stores information on the sweep wave number band inputted in advance. The sweep frequency bands B ₁ , B ₂ , B ₃ , . . . are obtained by subdividing the sweep frequency range of the sweep signal generator 12 into small sections. The variable level control means 24 changes the level amount of the variable level device 15 in pre-measurement processing until an output signal is output from the comparator 17.
The set value signal is sent out until the comparator 17 issues an output signal. In other words, spurious signals are searched on a level-by-level basis. The frequency value reading storage means 25 reads the current sweep frequency of the sweep signal generator 12 based on the output signal from the comparator 17, and stores the frequency. The calculation means 26 reads the information of the sweep frequency band stored in the sweep frequency band storage means 23, and calculates the center FC of the sweep frequency from the number of sweeps Ni and the sweep width S, which are the sweep conditions of the sweep signal generator 12. For example, the lower limit frequency of the sweep frequency band in the sweep signal generator 12 is
When F ₁ and the upper limit frequency are F ₂ , FC=F ₁ +SNi−S/2Ni×0.01 Nmax=F ₂ −F ₁ /S The center FC of the sweep frequency is obtained.

Here, the number of sweeps Ni = 1, 2, 3, ..., constant 0.01
represents the overlap fraction. The signal generator control means 27 sets the center FC of the sweep frequency calculated by the calculation means 26 to the sweep signal generator 12 based on the signal from the sweep control means 28, thereby determining the center of the sweep frequency. Sweep control means 28 is variable level control means 2
4, or by the sawtooth wave output end signal from the sawtooth wave generation circuit 19, a sawtooth wave is newly output from the sawtooth wave generation circuit 19. Sends data to generate wave voltage. Note that when the output signal is output from the comparator 17,
The function of the sawtooth wave generation circuit 19 is temporarily stopped, and the frequency of the counter 18 at that time is controlled by the control unit 20.
, and the value thereof is stored in the frequency value reading storage means 25. However, when the output signal is output from the comparator 17, the sweep signal generator 1
If the frequency value reading storage means 25 can access the second sweep frequency, for example, if the sweep speed is slow, it is not necessary to temporarily stop the function of the sawtooth wave generation circuit 19 using the output signal of the comparator 17.

The operation of the present invention configured as described above will be explained using the flowchart shown in FIG.

First, the following process is performed as pre-processing for measurement.
That is, the NQ sensitivity of the measured wave FM receiver 14 is measured (step 31). The level of the desired signal generator 11 at the sensitivity point at that time is measured. Now let the level be XdBμ, set the output level of the desired wave signal generator 11 to (X + 40) dBμ (step
32). The output level of the sweep signal generator 12 is set to (X+20) dBμ, which is 20 dB lower than that of the desired wave signal generator 11 (step 33). Data is sent from the sweep control means 28 to the sawtooth wave generation circuit 19. As a result, the sawtooth voltage is sent from the sawtooth wave generation circuit 19 to the sweep signal generator 12.
A sweep frequency is generated from step 2 (step 34). The center of the sweep frequency at this time is FM receiver 1 under test.
4, and the sweep frequency width of the sweep signal generator 12 is equal to the reception bandwidth of the FM receiver 14 under test. In this frequency sweep, desired wave signal generation 1
The above-mentioned beat interference occurs due to the desired wave signal from 1 and the interference signal from the sweep signal generator 12,
A butterfly-shaped composite wave is generated in the output of the FM receiver 14 to be measured. This butterfly-shaped composite wave is detected by the beat detection section 16.
When the peak value of the detected beat interference wave is smaller than a predetermined level, that is, when the spurious is small, the variable level control means 24 outputs a variable level to search for the spurious in terms of level. The level amount of the device 15 is reset in sequence every time the frequency sweep is completed (step
34, 35, 36). In this way, the variable level device 15
As the set level amount changes, an output signal is output from the comparator 17 (step 35), the setting of the level amount of the variable leveler 15 is completed, and the output level of the desired wave signal generator 11 is set. Further, the output level of the sweep signal generator 12 is set to the sum of the output level of the desired wave signal generator 11 and the spurious response ratio (DB) desired to be detected (step 37). This completes the measurement pre-processing.

Thereafter, the sweep frequency band storage means 23 is accessed via the sweep control means 28 to read information on the sweep frequency band. This information is input to the calculation means 26, and the calculation means 26 calculates the sweep frequency band, the number of sweeps, and the center of the sweep frequency that define the sweep conditions of the sweep signal generator 12. Data at the center of this sweep frequency is sent from the signal generator control means 27 to the sweep signal generator 12. Now sweep signal generator 1
Assume that the center FC ₁ of the sweep width S ₁ shown in FIG. 7 is set at 2. Sweep data is sent from the sweep control means 28 to a sawtooth wave generation circuit 19, and a sawtooth wave voltage is sent out from the sawtooth wave generation circuit 19 to the sweep signal generator 12. As a result, a sweep frequency having a sweep width _S1 centered at _FC1 is output from the sweep signal generator 12 (step 38). When the frequency sweep of the sweep width S ₁ is completed, an end signal indicating that the frequency sweep of the sweep width S ₁ has been completed is sent from the sawtooth wave generation circuit 19 to the sweep control means 28 (step
40), the calculation means 26 accesses the sweep frequency band storage means 23 in order to frequency sweep the next sweep width _S2 . Then, the calculation means 26 calculates the center FC ₂ of the next sweep frequency using the above-mentioned formula. Then, the center FO ₂ of the sweep frequency is set via the signal generator control means 27, and the sweep data is sent from the sweep control means 28, thereby performing a frequency sweep with a sweep width _S2 (step 41). , 42, 43). In this way, the sweep width is changed one after another, and the frequency sweep of the sweep frequency band _B1 is performed. After the frequency sweep of the sweep frequency band _B1 is performed, the sweep frequency band storage means 23 is accessed, the center FC of the sweep frequency of each sweep width in the sweep frequency band _B2 is calculated, and the sweep is repeated (step 43,
44). The above steps are repeated to perform a frequency sweep over the entire sweep frequency band, that is, the entire sweep frequency range, but as described above, the frequency sweep is performed with the sweep widths S ₁ and S ₂ partially overlapping. If there is a spurious response during the frequency sweep of each sweep width, that is, if an output signal is output from the comparator 17, the sawtooth voltage output from the sawtooth wave generation circuit 19 is stopped at the level at that time, and a sweep signal is generated. Stop sweeping the container 12. Then, the frequency value reading storage means 25 reads the frequency of the counter 18 and stores the frequency (steps 39, 45,
46, 47). The sweep control means 28 subsequently sends the sweep data to the stopped sawtooth wave generation circuit 19, and the sweep signal generator 12 resumes the frequency sweep (step 48).

If the composite wave outputted from the output end of the FM receiver 14 under test includes an interference beat of a predetermined level or higher, the comparator 17 outputs an output signal. As a result, it is determined that spurious is present, and the sweep frequency at that time is stored in the frequency value reading storage means 25. In this way, a frequency sweep is performed while changing the sweep frequency band one after another over the entire sweep frequency range, and the presence or absence of a spurious response is automatically determined, and if there is a spurious response, that frequency is used for frequency value reading. It is stored in the storage means 25. By displaying the frequency stored in the frequency value reading storage means 25 on the display device 22 and performing spurious detection on the displayed frequency based on the NQ method stipulated by the Radio Law, the level value can be obtained extremely quickly. .

In FIG. 5, the level amount of the variable level device 15 is made variable, and the level of the comparator 17 is made constant beforehand and compared with the peak value of the interference beat. It is also possible to make the comparison voltage of the comparator 17 variable while keeping the reference voltage constant. However, in the configuration shown in FIG. 5, the level of the composite wave output from the FM receiver under test 14 is superior in terms of S/N, so the comparison level of the comparator 17 is kept constant. be.

As explained above, according to the present invention, it is possible to automatically measure the occurrence frequency of a spurious response without relying on human hearing, and the sweep speed for searching for a spurious response can be increased. A spurious response measuring device is realized in which the time required for response search is shortened and accurate measurements can be made without omission.

[Brief explanation of the drawing]

Figure 1 is a basic configuration diagram of the swept wave interferometric measurement method for spurious responses, and Figures 2 and 3 are the measurement target.
Figure 4 is a waveform diagram of the composite wave output to the output end of the FM receiver. Figure 4 is a diagram of the detected interference beat waveform. Figure 5 is a diagram of the detected interference beat waveform.
The figure shows the configuration of an embodiment of the spurious response device according to the present invention, FIG. 6 is an explanatory diagram of a sweep band, and FIG. 7 is an explanatory diagram of sweep settings for explaining the method of sweeping. In the figure, 1 is a standard signal generator, 2 is a frequency sweep signal generator, 3 is a matching device, 4 is an FM receiver to be measured,
5 is a high-pass filter, 6 is a rectifier, 7 is a low-pass filter, 11 is a desired wave signal generator, 12 is a sweep signal generator, 13 is a matching box, and 14 is an FM to be measured.
Receiver, 15 is a variable leveler, 16 is a beat detection section, 17 is a comparator, 18 is a counter, 19
2 is a sawtooth wave generating circuit, 20 is a control section, 21 is an input key, and 22 is a display device.

Claims (1)

[Scope of utility model registration request] A desired wave signal generator 11 that generates a frequency signal of a desired wave, a sweep signal generator 12 that generates a swept frequency signal as an interference wave, a matching box 13 that superimposes the desired wave and the interference wave, and a desired wave and an interference wave. A variable level device that applies a signal superimposed with interference waves to the input terminal of the FM receiver to be measured 14, receives a composite wave of the Z-shaped output and the interference beat generated at its output terminal, and varies the level of the composite wave. 15, a beat detection unit 16 that obtains a detected waveform of an interference beat from the composite wave whose level has been adjusted by the variable level device 15, and a peak value and a predetermined level of the detected waveform detected by the beat detection unit 16. Comparator 1 to compare with
7, a sawtooth wave generation circuit 19 that supplies a sawtooth wave to the sweep signal generator 12, and a desired wave signal generator 1.
1. The control unit 20 includes a control unit 20 that controls the sweep signal generator 12 and the variable level generator 15, and the control unit 20 controls the sawtooth wave generation circuit 19 to generate the sweep signal generator 12.
A sweep control means 28 generates the sweep frequency signal corresponding to the center frequency and frequency band of the FM receiver 14 to be measured, and when no output signal is output from the comparator 17 in the level search preprocessing prior to the main measurement, the sweep control means 28 a variable level control means 24 which instructs the control means 28 to sweep, controls the variable level device 15 for each sweep to cause the comparator 17 to output an output signal, and sets the measurement level;
The sweep control means 28 that receives the level setting completion signal from the variable level control means 24 is connected to the sawtooth wave generation circuit 1.
9 to cause the sweep signal generator 12 to sweep,
The frequency value reading storage means 25 reads and stores the frequency of the sweep signal generator 12 when the comparator 17 outputs an output signal, and the sweep signal generator 1 uses the information stored in the sweep frequency band storage means 23.
and a signal generator control means 27 for controlling the
A spurious response device that reads the spurious frequency of the FM receiver under test.