JP5945615B1 - Signal measuring apparatus, signal measuring system, and signal measuring method - Google Patents

Abstract

A signal measuring apparatus, a signal measuring system, and a signal measuring method capable of measuring an image signal without separating them are provided. When a level of a signal to be measured corresponding to a frequency less than a target frequency that is a measurement target of the signal under measurement is measured by the measurement unit, the control unit calculates the mixing signal from the measurement frequency of the signal under measurement. When the local oscillator is controlled so that the frequency obtained by subtracting the frequency becomes the specified frequency (step S2), and the level of the measurement target signal corresponding to the frequency equal to or higher than the target frequency is measured by the measurement unit, the frequency of the mixing signal Then, the local oscillator is controlled so that the frequency obtained by subtracting the measurement frequency of the signal under measurement becomes the specified frequency (step S3). [Selection] Figure 6

Description

  The present invention relates to a signal measuring apparatus, a signal measuring system, and a signal measuring method for measuring the level of a broadband signal in units of frequency.

  Conventionally, when measurement is performed by converting a signal under measurement into a signal having an intermediate frequency Fi using a frequency sweep signal, a first measurement process for obtaining measurement data using a sweep signal having a frequency obtained by adding the intermediate frequency Fi to a frequency within a set frequency range. And a second measurement process for obtaining measurement data using a sweep signal having a frequency obtained by subtracting the intermediate frequency Fi from a frequency in the set frequency range, and obtaining the measurement data obtained in the first measurement process and the second measurement process. Patent Document 1 proposes a technique for separating data other than a desired signal without requiring a preselector by obtaining all data having the same value and data having the minimum value for each measurement frequency point with respect to the measured data. .

Japanese Patent No. 3797556

  However, in the conventional technique as described above, since the measurement with the sweep signal must be performed twice in the first measurement process and the second measurement process, the execution time and the second measurement required for the first measurement process are required. There has been a problem that it is impossible to accurately measure a signal whose characteristics change with the passage of time due to the execution time required for the process.

  The present invention has been made to solve such a problem, and a signal measuring device, a signal measuring system, and a signal measuring device capable of accurately measuring even a signal whose characteristics change with the passage of time. It aims to provide a method.

  The signal measuring apparatus of the present invention includes a local oscillator (20) that generates a local oscillation signal, and a control unit (21) that controls the local oscillator so that the frequency of the local oscillation signal changes between predetermined frequency regions. And a measurement unit (35) for measuring a level of a signal to be measured having a specified frequency obtained by mixing the signal under measurement with a mixing signal obtained by multiplying the local oscillation signal, and the control unit includes the signal under measurement. When the level of the measurement target signal corresponding to a frequency less than the target frequency of the measurement target is measured by the measurement unit, the frequency obtained by subtracting the frequency of the mixing signal from the measurement frequency of the signal under measurement is The local oscillator is controlled so as to have a specified frequency, and the level of the measurement target signal corresponding to a frequency equal to or higher than the target frequency is measured by the measurement unit. The case has a configuration in which the a frequency of the mixing signal frequency obtained by subtracting the measured frequency of the signal to be measured for controlling the local oscillator such that the prescribed frequency.

  With this configuration, when measuring the level of the measurement target signal corresponding to a frequency lower than the target frequency, the signal measurement device of the present invention has a frequency obtained by subtracting the frequency of the mixing signal from the measurement frequency of the signal under measurement. In order to generate the local oscillation signal, an image signal of the target frequency component of the signal under measurement is generated in a frequency region below the measurement frequency.

  In the signal measuring apparatus of the present invention, when measuring the level of the signal to be measured corresponding to a frequency equal to or higher than the target frequency, the frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency. Thus, in order to generate the local oscillation signal, an image signal of the target frequency component of the signal under measurement is generated in a frequency region above the measurement frequency.

  As described above, the signal measurement apparatus of the present invention controls the frequency of the local oscillation signal so that the frequency band of the image signal of the target frequency component of the signal under measurement is not included in the measurement frequency of the signal under measurement. Since an image signal is not generated at a frequency, even a signal whose characteristics change with time can be accurately measured.

  The control unit may set the target frequency to be the center frequency of the frequency band used by the test object that generates the signal under measurement.

  Further, the specified frequency may be set to be larger than a quarter of a width of a frequency band used by the test object.

  With this configuration, the signal measuring apparatus of the present invention can prevent an image signal of a frequency component in the frequency band used by the test object from being generated in the frequency band used by the test object. it can.

  The signal measurement system of the present invention includes a frequency conversion device (2) that converts a signal under measurement into a signal in an intermediate frequency band, and a signal that measures the level of the signal under measurement converted into the intermediate frequency band by the frequency conversion device. A local oscillator (20) for generating a local oscillation signal, and the local oscillator so that the frequency of the local oscillation signal changes between predetermined frequency regions. The frequency converter includes a multiplier (12) that multiplies the local oscillation signal generated by the local oscillator, and the local oscillation signal is multiplied by the multiplier. And a mixer (14) for mixing the signal under measurement with the mixed signal, and the signal measuring device is a signal to be measured having a specified frequency mixed by the mixer The measurement unit (35) for measuring the level is further provided, and the control unit measures the level of the measurement target signal corresponding to a frequency less than a target frequency as a measurement target of the signal under measurement by the measurement unit. In this case, the local oscillator is controlled such that the frequency obtained by subtracting the frequency of the mixing signal from the measurement frequency of the signal under measurement becomes the specified frequency, and the signal to be measured corresponding to the frequency equal to or higher than the target frequency is controlled. When the level is measured by the measurement unit, the local oscillator is controlled so that a frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency. .

  With this configuration, when the signal measurement system of the present invention measures the level of the measurement target signal corresponding to a frequency less than the target frequency, the frequency obtained by subtracting the frequency of the mixing signal from the measurement frequency of the signal under measurement is the specified frequency. In order to generate the local oscillation signal, an image signal of the target frequency component of the signal under measurement is generated in a frequency region below the measurement frequency.

  Further, in the signal measurement system of the present invention, when measuring the level of the measurement target signal corresponding to a frequency equal to or higher than the target frequency, the frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency. Thus, in order to generate the local oscillation signal, an image signal of the target frequency component of the signal under measurement is generated in a frequency region above the measurement frequency.

  As described above, the signal measurement system of the present invention performs measurement by controlling the frequency of the local oscillation signal so that the frequency band of the image signal of the target frequency component of the signal under measurement is not included in the measurement frequency of the signal under measurement. Since an image signal is not generated at a frequency, even a signal whose characteristics change with time can be accurately measured.

  The signal measuring method of the present invention includes a local oscillator (20) that generates a local oscillation signal, and a control unit (21) that controls the local oscillator so that the frequency of the local oscillation signal changes between predetermined frequency regions. And a measurement unit (35) for measuring a level of a measurement target signal having a specified frequency in which a signal under measurement is mixed with a mixing signal obtained by multiplying the local oscillation signal. When the level of the measurement target signal corresponding to a frequency less than the target frequency that is the measurement target of the signal under measurement is measured by the measurement unit, the frequency of the mixing signal is calculated from the measurement frequency of the signal under measurement. The control unit controls the local oscillator so that the subtracted frequency becomes the specified frequency, and the level of the measurement target signal corresponding to the frequency equal to or higher than the target frequency is the previous level. When measured by the measurement unit, the control unit such that the the frequency is the frequency obtained by subtracting the measured frequency of the signal to be measured becomes the prescribed frequency of the mixing signal for controlling the local oscillator.

  Therefore, in the signal measurement method of the present invention, when measuring the level of the measurement target signal corresponding to a frequency less than the target frequency, the frequency obtained by subtracting the frequency of the mixing signal from the measurement frequency of the signal under measurement becomes the specified frequency. Thus, in order to generate the local oscillation signal, the image signal of the target frequency component of the signal under measurement is generated in a frequency region below the measurement frequency.

  In the signal measurement method of the present invention, when measuring the level of the signal to be measured corresponding to a frequency equal to or higher than the target frequency, the frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency. Thus, in order to generate the local oscillation signal, an image signal of the target frequency component of the signal under measurement is generated in a frequency region above the measurement frequency.

  As described above, the signal measurement method of the present invention measures the frequency of the local oscillation signal so that the frequency band of the image signal of the target frequency component of the signal under measurement is not included in the measurement frequency of the signal under measurement. Since an image signal is not generated at a frequency, even a signal whose characteristics change with time can be accurately measured.

  According to the present invention, it is possible to perform measurement under conditions where no image signal is generated. As a result, the present invention is a signal whose characteristics change with the passage of time, which has been a problem of the technique proposed in Patent Document 1 because the image signal was swept twice to separate it. It is possible to provide a signal measuring device, a signal measuring system, and a signal measuring method capable of measuring the signal.

FIG. 1 is a block diagram of a signal measurement system according to an embodiment of the present invention. FIG. 2 is a first conceptual diagram for explaining control of a local oscillation signal by the signal measuring apparatus according to the embodiment of the present invention. FIG. 3 is a second conceptual diagram for explaining the control of the local oscillation signal by the signal measuring apparatus according to the embodiment of the present invention. FIG. 4 is a first conceptual diagram for explaining the condition of the specified frequency set in the signal measuring apparatus according to the embodiment of the present invention. FIG. 5 is a second conceptual diagram for explaining the condition of the specified frequency set in the signal measuring apparatus according to the embodiment of the present invention. FIG. 6 is a flowchart showing a local oscillation signal control operation by the signal measuring apparatus according to the embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  As shown in FIG. 1, the signal measurement system 1 measures a level conversion device 2 that converts a signal under measurement into a signal in the intermediate frequency band, and a level of the signal under measurement converted into the intermediate frequency band by the frequency conversion device 2. The signal measuring device 3 is provided.

  The frequency conversion device 2 includes an HPF (High-pass Filter) 10 that removes the offset of the local oscillation signal input from the signal measurement device 3, an amplifier 11 that amplifies the local oscillation signal that has passed through the HPF 10, and an amplification by the amplifier 11. A multiplier 12 that multiplies the local oscillation signal, a BPF (Band-pass Filter) 13 that passes a specific frequency band component of the mixing signal multiplied by the local oscillation signal, and a mixing signal that passes through the BPF 13 A mixer 14 for mixing the signal, an amplifier 15 for amplifying the measurement signal mixed by the mixer 14, and an LPF (Low-pass Filter) 16 for removing high-frequency components from the measurement signal amplified by the amplifier 15. Consists of including.

  In the present embodiment, the multiplier 12 is described as increasing the frequency of the local oscillation signal by 10 times, but may be appropriately changed depending on the design. The BPF 13 is set with a coefficient so as to pass a frequency band corresponding to the test object for generating the signal under measurement.

  In the present embodiment, the signal to be measured is described as being received by the frequency converter 2 through the waveguide, but the signal to be measured is received by the frequency converter 2 through another medium such as a coaxial cable. In this case, the coefficient of the BPF 13 may be set from the signal measuring device 3 side.

  The measurement signal that has passed through the LPF 16 is output to the signal measurement device 3. In the present embodiment, the frequency band of the signal under measurement mixed by the mixer 14 is 60 to 90 GHz, which is an E-band in the millimeter wave band.

  The mixer 14 outputs a measurement signal of 2 GHz as a specified frequency. Therefore, the BPF 13 is set so as to pass a frequency component of 58 to 92 GHz when the entire band of the E-band signal under measurement is to be measured.

  The signal measuring device 3 includes a local oscillator 20 that generates a local oscillation signal, a control unit 21 that controls the local oscillator 20 so that the frequency of the local oscillation signal changes between predetermined frequency regions, and an offset of the local oscillation signal. And a local oscillation signal that has passed through the HPF 22 is output to the frequency converter 2.

  The control unit 21 is configured by a computer device, for example. The computer device includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a non-volatile storage medium such as a hard disk device, and various input / output ports. .

  The ROM and the hard disk device of this computer device store a program for causing the computer device to function as the control unit 21. That is, when the CPU executes a program stored in the ROM using the RAM as a work area, the computer device functions as the control unit 21.

  The control unit 21 has a measurement band of the signal under measurement, a target frequency as a measurement target of the signal under measurement, various parameters such as various setting values for display, a command for instructing start and end of the test, etc. An operation unit 23 is provided.

  For example, when the entire band of the E-band signal under measurement is to be measured, the control unit 21 has a predetermined frequency region (for example, the operation unit 23 or the like) out of 58 to 92 GHz that is the frequency region of the mixing signal. The local oscillator 20 is controlled so that the frequency of the local oscillation signal changes at a predetermined frequency interval (for example, the frequency interval set via the operation unit 23) over the frequency range set via ing.

  Since the present embodiment uses a signal obtained by multiplying the frequency of the local oscillation signal generated by the local oscillator 20 by 10 times by the multiplier 12 as the mixing signal, the control unit 21 uses the local signal generated by the local oscillator 20. The local oscillator 20 is controlled so that the frequency of the oscillation signal changes between 5.8 and 9.2 GHz.

  The signal measurement device 3 includes an LPF 30 that removes noise components from the measurement signal input from the frequency conversion device 2, a local oscillator 31 that generates a local oscillation signal for frequency conversion of the measurement signal, and a local oscillator 31. A mixer 32 that mixes the measurement signal with the generated local oscillation signal, a BPF 33 that extracts a measurement target signal from the signal mixed by the mixer 32, and an A / D that converts the measurement target signal that has passed through the BPF 33 into a digital signal (Analog to Digital) The converter 34, the measurement part 35 which measures the level of the measuring object signal converted into the digital signal, and the display part 36 for displaying the measurement result by the measurement part 35 are comprised further. .

  In the present embodiment, the local oscillator 31 generates a 0.9 GHz local oscillation signal in order to convert the 2 GHz measurement signal into a 0.1 GHz measurement target signal by the mixer 32.

  Therefore, the BPF 33 has a coefficient set so as to pass the measurement target signal in the 0.1 GHz band. The measurement unit 35 is configured by, for example, a CPU that constitutes the control unit 21, and measures the level of the measurement target signal in accordance with control by the control unit 21.

  The control unit 21 is provided with a display control unit 37 that controls the display of the display unit 36. For example, the control unit 21 controls the display control unit 37 so as to display the measurement result screen on the display unit 36. The display control unit 37 includes, for example, a CPU and a video card that configure the control unit 21.

  When the level of the measurement target signal corresponding to a frequency lower than the target frequency is measured by the measurement unit 35, the control unit 21 obtains the specified frequency by subtracting the frequency of the mixing signal from the measurement frequency of the signal under measurement. Thus, the local oscillator 20 is controlled.

  Further, when the level of the measurement target signal corresponding to a frequency equal to or higher than the target frequency is measured by the measurement unit 35, the control unit 21 determines that the frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal The local oscillator 20 is controlled so that

  In the present embodiment, the control unit 21 sets the center frequency of the frequency band used by the test object that generates the signal under measurement as the target frequency. Note that the control unit 21 may set the lowest frequency as the target frequency or the highest frequency as the target frequency as long as it is within the frequency band used by the test object that generates the signal under measurement.

  In the following description, the target frequency is 80 GHz. That is, in this embodiment, the level of the signal under test transmitted by the object under test using a frequency band having a center frequency of 80 GHz is measured in frequency units.

  As shown in FIG. 2, for example, when measuring the level of a 76 GHz frequency component of the signal under measurement, the control unit 21 controls the local oscillator 20 so that the frequency of the mixing signal is 74 GHz or 78 GHz.

  Here, when the control unit 21 controls the local oscillator 20 so that the frequency of the mixing signal becomes 78 GHz, the image signal Siu of the target frequency component of the signal under measurement is generated at 76 GHz which is the measurement frequency.

  In this case, the control unit 21 controls the local oscillator 20 so that the frequency of the mixing signal becomes 74 GHz, so that the frequency of the image signal is set to 68 GHz. It is possible to avoid the influence of the image signal at the time of measurement and the spurious accompanying the image signal on the measurement result.

  As described above, when the control unit 21 measures the level of the measurement target signal corresponding to 76 GHz that is less than the target frequency 80 GHz, the frequency of the mixing signal is 74 GHz (= measurement frequency 76 GHz−specified frequency 2 GHz). By causing the local oscillator 20 to generate a local oscillation signal, an image signal Sil for a signal in the target frequency band of 80 GHz band is generated in the 68 GHz band less than the measurement frequency.

  As shown in FIG. 3, for example, when measuring the level of the 84 GHz frequency component of the signal under measurement, the control unit 21 controls the local oscillator 20 so that the frequency of the mixing signal is 82 GHz or 86 GHz.

  Here, when the control unit 21 controls the local oscillator 20 so that the frequency of the mixing signal becomes 82 GHz, the image signal Sil of the target frequency component of the signal under measurement is generated at 84 GHz as the measurement frequency.

  In this case, the control unit 21 controls the local oscillator 20 so that the frequency of the mixing signal is 86 GHz, so that the frequency of the image signal is set to 92 GHz. It is possible to avoid the influence of the image signal at the time of measurement and the spurious accompanying the image signal on the measurement result.

  As described above, when the control unit 21 measures the level of the measurement target signal corresponding to the target frequency of 80 GHz or higher and 84 GHz, the control signal is locally so that the frequency of the mixing signal is 86 GHz (= measurement frequency 84 GHz + specified frequency 2 GHz). By causing the oscillator 20 to generate a local oscillation signal, an image signal Siu for a signal in the target frequency band of 80 GHz band is generated in the 92 GHz band that is equal to or higher than the measurement frequency.

  In the present embodiment, the specified frequency has been described as 2 GHz. However, the specified frequency is set to be larger than a quarter of the width of the frequency band used by the test object. In the following description, the width of the frequency band Fb used by the object to be tested is BW, the specified frequency is IF, and the band in which the image signal of the frequency band Fb used by the object to be tested is generated is Fbil and Fbih.

  As shown in FIG. 4, in a state where the specified frequency IF is relatively low with respect to the width BW, the frequency components in the frequency band Fb used by the test object are within the frequency band Fb used by the test object. The image signal will be generated.

  In the state shown in FIG. 4, overlaps Oll and Olh exceeding the target frequency Fc occur between the frequency band Fb and the image signal bands Fbil and Fbih. Assuming that the frequency included in the portions corresponding to the overlaps Oll and Olh is the measurement frequency, the image signal of the frequency component in the frequency band Fb used by the object under test affects the signal of the measurement frequency.

  In order not to generate overlaps Oll and Olh exceeding the target frequency Fc between the frequency band Fb and the bands Fbil and Fbih, (IF × 2) − (BW / 2)> 0, that is, IF> BW / 4 needs to be satisfied.

  By setting the prescribed frequency so as to satisfy this condition, as shown in FIG. 5, an image of frequency components in the frequency band Fb used by the object under test within the frequency band Fb used by the object under test. The generation of a signal can be prevented.

  The local oscillation signal control operation by the signal measuring apparatus 3 according to the embodiment of the present invention configured as described above will be described with reference to FIG. Note that the local oscillation signal control operation described below is executed every time measurement is performed at each measurement frequency.

  First, the control unit 21 determines whether or not the level of the measurement target signal corresponding to a frequency less than the target frequency is measured by the measurement unit 35 (step S1). Here, when it is determined that the level of the measurement target signal corresponding to a frequency less than the target frequency is measured by the measurement unit 35, the control unit 21 subtracts the frequency of the mixing signal from the measurement frequency of the signal under measurement. The local oscillator 20 is controlled so that the frequency becomes the specified frequency (step S2), and the local oscillation signal control operation for this measurement frequency is terminated.

  On the other hand, when it is determined that the level of the measurement target signal corresponding to the frequency less than the target frequency is not measured by the measurement unit 35, that is, the level of the measurement target signal corresponding to the frequency equal to or higher than the target frequency is measured by the measurement unit 35. The control unit 21 controls the local oscillator 20 so that the frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency (step S3), and the local oscillation signal control operation for the measurement frequency is performed. Exit.

  As described above, in the signal measurement method according to the present embodiment, the measurement unit 35 measures the level of the measurement target signal corresponding to the frequency less than the target frequency as the measurement target of the signal under measurement using the signal measurement device 3. In this case, the control unit 21 controls the local oscillator 20 so that the frequency obtained by subtracting the frequency of the mixing signal from the measurement frequency of the signal under measurement becomes the specified frequency, and the level of the measurement target signal corresponding to the frequency equal to or higher than the target frequency. Is measured by the measurement unit 35, the control unit 21 controls the local oscillator 20 so that the frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency.

  As described above, in the present embodiment, when measuring the level of a measurement target signal corresponding to a frequency less than the target frequency, the frequency obtained by subtracting the frequency of the mixing signal from the measurement frequency of the signal under measurement is specified. In order to generate the local oscillation signal to have the frequency, an image signal of the target frequency component of the signal under measurement is generated in a frequency region below the measurement frequency.

  Further, in the present embodiment, when measuring the level of the measurement target signal corresponding to a frequency equal to or higher than the target frequency, the frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency. In order to generate the local oscillation signal, an image signal of the target frequency component of the signal under measurement is generated in a frequency region above the measurement frequency.

  As described above, in this embodiment, the frequency of the local oscillation signal is controlled so that the frequency band of the image signal of the target frequency component of the signal under measurement is not included in the measurement frequency of the signal under measurement. Since no image signal is generated, even a signal whose characteristics change with the passage of time can be measured accurately.

  Further, in the present embodiment, it is not necessary to perform two measurements using the local oscillation signal as a sweep signal, so that the time required for measurement can be shortened as compared with the conventional technique. Furthermore, since this embodiment can shorten the time required for measurement compared with the conventional technique, the frequency that can be measured within the same measurement time can be increased, and the frequency resolution of the measurement result can be increased. can do.

  Although the embodiments of the present invention have been disclosed above, it is obvious that those skilled in the art can make modifications without departing from the scope of the present invention. All such modifications and equivalents are intended to be included in the claims recited in the claims.

DESCRIPTION OF SYMBOLS 1 Signal measuring system 2 Frequency converter 3 Signal measuring device 12 Multiplier 14 Mixer 20 Local oscillator 21 Control part 35 Measuring part

Claims (5)

A local oscillator (20) for generating a local oscillation signal;
A control unit (21) for controlling the local oscillator so that the frequency of the local oscillation signal changes between predetermined frequency regions;
A measurement unit (35) for measuring the level of a signal to be measured having a specified frequency in which a signal under measurement is mixed with a mixed signal obtained by multiplying the local oscillation signal;
The controller is
When the level of the measurement target signal corresponding to a frequency less than the target frequency that is the measurement target of the signal under measurement is measured by the measurement unit, the frequency of the mixing signal is subtracted from the measurement frequency of the signal under measurement. The local oscillator is controlled so that the specified frequency becomes the specified frequency,
When the level of the measurement target signal corresponding to a frequency equal to or higher than the target frequency is measured by the measurement unit, a frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency. A signal measuring device for controlling the local oscillator.   The signal measuring apparatus according to claim 1, wherein the control unit uses a center frequency of a frequency band used by an object to be tested that generates the signal under measurement as the target frequency.   The signal measuring apparatus according to claim 1, wherein the specified frequency is set to be larger than a quarter of a frequency band width used by the object to be tested. A frequency converter (2) for converting the signal under measurement into a signal in the intermediate frequency band;
A signal measuring device (3) for measuring the level of the signal under measurement converted into the intermediate frequency band by the frequency converting device,
The signal measuring device includes a local oscillator (20) that generates a local oscillation signal, and a control unit (21) that controls the local oscillator so that the frequency of the local oscillation signal changes between predetermined frequency ranges, Have
The frequency converter includes a multiplier (12) for multiplying a local oscillation signal generated by the local oscillator, and a mixer (14) for mixing the signal under measurement with a mixing signal obtained by multiplying the local oscillation signal by the multiplier. ) And
The signal measuring device further includes a measuring unit (35) that measures the level of a signal to be measured having a specified frequency mixed by the mixer.
The controller is
When the level of the measurement target signal corresponding to a frequency less than the target frequency that is the measurement target of the signal under measurement is measured by the measurement unit, the frequency of the mixing signal is subtracted from the measurement frequency of the signal under measurement. The local oscillator is controlled so that the specified frequency becomes the specified frequency,
When the level of the measurement target signal corresponding to a frequency equal to or higher than the target frequency is measured by the measurement unit, a frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency. Signal measuring system for controlling the local oscillator. A local oscillator (20) for generating a local oscillation signal;
A control unit (21) for controlling the local oscillator so that the frequency of the local oscillation signal changes between predetermined frequency regions;
Using a signal measuring device (3) comprising a measuring unit (35) for measuring the level of a signal to be measured having a specified frequency in which a signal under measurement is mixed with a mixing signal obtained by multiplying the local oscillation signal,
When the level of the measurement target signal corresponding to a frequency less than the target frequency that is the measurement target of the signal under measurement is measured by the measurement unit, the frequency of the mixing signal is subtracted from the measurement frequency of the signal under measurement. The control unit controls the local oscillator so that the specified frequency becomes the specified frequency,
When the level of the measurement target signal corresponding to a frequency equal to or higher than the target frequency is measured by the measurement unit, a frequency obtained by subtracting the measurement frequency of the signal under measurement from the frequency of the mixing signal becomes the specified frequency. The signal measuring method in which the control unit controls the local oscillator.

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