JP5007834B2 - Control method for avoiding image interference signal in measurement of overwrite characteristic, and control device therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive apparatus by eliminating a complicated circuit of a measurement instrument for counter measure against image disturbance to measure an overwrite characteristic. <P>SOLUTION: The apparatus determines a local frequency used for measuring the overwrite characteristic, determines whether there is an image frequency having a signal detectable frequency component other than a known frequency component recorded on a recording medium by using the predetermined overwrite frequency within a frequency band calculated by sum or difference of the determined local frequency and central frequency of an intermediate frequency filter, and modifies the local frequency so as not to detect the frequency component of the image frequency when there is the image frequency having the signal detectable frequency component other than the known frequency component recorded on the recording medium within the calculated frequency band. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for measuring an overwrite characteristic of a recording medium, and more particularly, to a control method for avoiding an image disturbing signal in measurement of an overwrite characteristic of a magnetic recording medium such as a hard disk, and a control apparatus therefor.

  One of the inspection items of an inspection apparatus for a recording medium such as a hard disk is overwrite measurement. The method of overwriting measurement is usually processed according to the following procedure.

  Procedure 1. A signal of frequency (1) is recorded on a desired track of the inspection medium.

  Procedure 2. A signal of frequency (2) is recorded on the track on which frequency (1) of procedure 1 is recorded.

  Procedure 3. The residual component of the overwritten frequency (1) is detected through a filter that extracts only the first recorded frequency (1) without passing the signal of the frequency (2) overwritten later.

  Procedure 4. A process is performed in which the overwrite characteristic of the inspection medium is grasped based on the magnitude of the residual component of the detected frequency (1).

  In this measurement, in the measurement described in the procedure 3 described in the above-described overwrite measurement method, a signal of frequency (2) is recorded on the measurement track of the inspection medium, and the amplitude thereof is a normal hard disk. The residual component of the frequency (1) that must be measured for grasping the overwrite characteristics of the signal is approximately -40 dB compared to the frequency (2). Very small.

  Usually, a spectrum analyzer is suitable for measuring such a signal having a large amplitude difference with high accuracy, and the spectrum analyzer is actually used for performance inspection at the research and development stage. However, in the inspection equipment for recording media such as hard disks, from the point of measurement speed, etc., a measuring instrument with performance equivalent to that of a pectrum analyzer and sufficient measuring speed is used as a dedicated measuring device for overwrite characteristics. Must be specially created and incorporated.

JP 2003-85701 A

  In the overwrite measurement in a magnetic recording medium inspection device such as a hard disk, the residual component of the first written signal that has been written to a specific track of the inspection medium once and overwhelmed with the signal has a very small amplitude. Must be detected. The signal state at this time includes a large amplitude signal recorded by overwriting, and the measurement frequency exists in a state where the amplitude ratio is less than 1% so as to be buried in the signal. In the overwrite measurement, the residual signal buried in this large amplitude signal must be discriminated and measured.

  Further, since the frequency of the signal to be measured must be an arbitrary frequency of the measurer, the frequency of the filtering function for discriminating the measurement frequency must be arbitrarily changed by the measurer.

  A heterodyne (frequency conversion) method is often used as a method for creating a filtering function of an arbitrary frequency.

  The basic components of the heterodyne system are a mixer for converting the frequency of the measurement signal, an intermediate frequency filter (IF filter) for extracting a specific frequency component of the frequency-converted signal, and a local signal for injection into the mixer A generator.

  In operation, a measurement signal is supplied to the mixer, and a signal having a frequency that is higher (measurement frequency + IF frequency) or lower (measurement frequency-IF frequency) by an intermediate frequency (IF frequency) is used as a local frequency to the mixer. In addition, the measurement signal can be converted into an IF frequency, and the state of the signal at the measurement frequency can be measured by measuring the signal at the IF frequency. Further, by changing the local frequency, it is possible to set and measure a desired frequency as the measurement frequency.

  However, in this configuration, when the local frequency Lo is set to Fm + IF (measurement frequency + intermediate frequency) in order to measure the measurement frequency Fm, the frequency Fi of the Lo-IF together with the frequency Fm is the frequency Fm to be measured. Is converted to an IF frequency with exactly the same sensitivity, and is superimposed on the measurement signal and measured. In the heterodyne type frequency converter, the frequency (Lo + IF) obtained by adding only the IF frequency to the local frequency Lo and the frequency (Lo-IF) obtained by subtracting only the IF frequency are simultaneously converted into the IF frequency.

  Of the input frequencies to the mixer determined by this addition and subtraction, the frequency on the frequency side that the operator does not intend as the measurement frequency is called the image frequency, and the frequency on the unintended side is converted to IF. A signal that is superimposed on the frequency to be measured is called an image interference signal.

  In order to remove this image interference signal, a variable frequency filter for filtering the image frequency is placed in front of the circuit, or a mixer for bringing the image frequency out of the measurement band, a local oscillator, A method is adopted in which a heterodyne circuit having an IF filter is installed to form a double heterodyne configuration.

  Such a measure of image disturbance is naturally performed in a commercially available spectrum analyzer, and a measurement circuit is configured with a similar circuit configuration in a conventional magnetic recording medium inspection device such as a hard disk. The circuit configuration of this measurement circuit is very complex, and the electronic components that are components are also expensive. Therefore, it is possible to prevent the device from becoming expensive by providing a switch circuit for sharing this overwrite measurement function with multiple channels. Etc. are devised.

  However, the measures for making these complicated circuit configurations are factors that further complicate the system configuration, and are one factor that increases the cost of the entire inspection apparatus for magnetic recording media such as hard disks.

  Accordingly, an object of the present invention is to omit a complicated circuit configuration for image interference countermeasures in measurement of overwrite characteristics, and to provide a low-cost device, a control method for avoiding image interference signals, and It is to provide the control device.

  The present invention relates to a control method for performing signal detection while avoiding an image frequency in measurement of an overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency, and measuring the overwrite characteristic Determining the local frequency used for the recording medium, and using the predetermined overwrite frequency in the recording medium within a frequency band calculated by the sum or difference between the determined local frequency and the center frequency of the intermediate frequency filter. Determining whether or not there is an image frequency having a signal detectable frequency component other than the known frequency component recorded in the above, and the known frequency recorded on the recording medium within the calculated frequency band. If there is an image frequency that has a frequency component that can detect signals other than the frequency component, the image As the frequency components of the wave is not detected, characterized in that comprising the step of changing the local frequency.

  The step of changing may include the step of changing the local frequency when the image frequency matches the overwrite frequency.

  The step of changing may include a step of changing the local frequency by the calculated frequency band to a low frequency side or a high frequency side of the overwrite frequency.

  The present invention relates to a control method for performing signal detection while avoiding an image frequency in measurement of an overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency, and measuring the overwrite characteristic Determining the local frequency used for the recording medium, and using the predetermined overwrite frequency in the recording medium within a frequency band calculated by the sum or difference between the determined local frequency and the center frequency of the intermediate frequency filter. Determining whether or not there is an image frequency having a signal detectable frequency component other than the known frequency component recorded in the above, and the known frequency recorded on the recording medium within the calculated frequency band. If there is an image frequency that has a frequency component that can detect signals other than the frequency component, the image As the frequency components of the wave is not detected, characterized in that comprising the step of changing the measurement write frequency used in the measurement of the overwrite characteristics.

  The step of changing may include a step of changing the write frequency for measurement when the image frequency matches the overwrite frequency.

  The step of changing is to change the write frequency for measurement within a measurable frequency range of the overwrite characteristic, and the passband of the intermediate frequency filter on the low frequency side or the high frequency side of the overwrite frequency A step of changing only the width may be included.

  The present invention is a computer-readable recording medium on which the above-described method executed by a computer is recorded.

  The present invention relates to a control apparatus for performing signal detection while avoiding an image frequency in measurement of an overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency, and measuring the overwrite characteristic The predetermined overwrite frequency is used for the recording medium within a frequency band calculated by means for determining a local frequency used for the recording medium and a sum or difference between the determined local frequency and the center frequency of the intermediate frequency filter. Means for determining whether there is an image frequency having a signal detectable frequency component other than the known frequency component recorded in this manner, and the known frequency recorded on the recording medium within the calculated frequency band. If there is an image frequency that has a frequency component that can detect signals other than the frequency component, the image As the frequency components of the wave is not detected, characterized in that and means for changing said local frequency.

  The present invention relates to a control apparatus for performing signal detection while avoiding an image frequency in measurement of an overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency, and measuring the overwrite characteristic The predetermined overwrite frequency is used for the recording medium within a frequency band calculated by means for determining a local frequency used for the recording medium and a sum or difference between the determined local frequency and the center frequency of the intermediate frequency filter. Means for determining whether there is an image frequency having a signal detectable frequency component other than the known frequency component recorded in this manner, and the known frequency recorded on the recording medium within the calculated frequency band. If there is an image frequency that has a frequency component that can detect signals other than the frequency component, the image As the frequency components of the wave is not detected, characterized in that and means for changing the measuring write frequencies used for the measurement of the overwrite characteristics.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First example]
A first embodiment of the present invention will be described with reference to FIGS.

<Outline of configuration>
Before describing the present invention in detail, an outline of a circuit configuration will be described.

  The present invention intends to measure the overwrite characteristic without receiving the image disturbing signal without using the above-described pre-variable filter for removing the image disturbing signal or the double heterodyne circuit.

  Compared with signal measurement performed by general-purpose measuring instruments such as spectrum analyzers, the measurement prerequisites for overwrite measurement in inspection equipment for recording media such as hard disks are narrowed down. In the recording medium inspection device such as a hard disk, the circuit device for countermeasures against image interference can be omitted if the measurement can be performed without receiving the image interference signal.

  In the case of a general-purpose spectrum analyzer, the measurement frequency is completely arbitrary, and when a specific frequency is observed, the input of any other frequency should not affect the result of the observed frequency.

  On the other hand, in a recording medium inspection device such as a hard disk, before performing the overwrite measurement, the first writing frequency (1) written to the recording medium to be inspected and the next written overwriting are performed. The signal frequency with the frequency (2) is arbitrarily set by the measurer. At the time of measurement, the measurement frequency (usually the same as the writing frequency (1) written first) and outside the observation band of the measurement frequency A certain overwritten frequency (2) is a known value, and signal components of other frequency components do not exist in the input signal.

  Therefore, in the present invention, under the measurement precondition in the recording medium inspection device such as a hard disk, when measuring the overwrite characteristic, the frequency component existing in the input signal other than the measurement frequency is only the frequency component of the overwritten signal. Since the image frequency generated from the local signal frequency to the heterodyne mixer that is set when observing the measurement frequency does not match the overwrite signal frequency, the image is disturbed by the signal because there is no other. It was designed taking into account that there was nothing.

  Hereinafter, the present invention will be described in detail.

<Circuit configuration>
FIG. 1 shows a schematic configuration of an inspection apparatus 100 constituting a simple heterodyne circuit according to the present invention.

  The inspection apparatus 100 includes a mixer 2 for frequency conversion of the measurement signal 1 of the measurement frequency Fm from the read signal amplification circuit 101, and an intermediate frequency filter (IF filter) for extracting a specific frequency component of the frequency converted signal. 3, an amplitude detector 4 that detects the amplitude of the extracted signal composed of a specific frequency component, a local frequency transmitter 6 that transmits a local signal 5 having a local frequency Lo to be injected into the mixer 2, A write frequency transmitter 8 for transmitting a write signal 7 of a write frequency (FL, FH) as a test signal used for measuring the write characteristics, a head control circuit 9 to which the write signal 7 is input, and a recording medium 102 (for example, Read / write head unit 10 for reading from or writing to a hard disk magnetic recording medium) and a local frequency A frequency setting circuit 11 for setting the local frequency Lo and the writing frequency (FL, FH) for the transmitter 6 and the writing frequency transmitter 8, respectively, and control of the setting of the local frequency Lo and the writing frequency (FL, FH). And a control circuit 12 for performing the above.

  The control circuit 12 receives the measurement frequency setting data 13 and inputs the local frequency calculation unit 15 that calculates the local frequency setting data 14 and the write frequency (FL, FH) setting data 16 and inputs the setting according to the setting change contents. Write frequency (FL, FH) calculation unit 17 that calculates changed data, image frequency calculation unit 18 that calculates image frequency using the calculated local frequency setting data 14, and image frequency that is calculated Is an image interference determination unit 19 that determines whether or not the image interference signal is superimposed on the measurement frequency to be measured, and the set frequency of the writing frequency (FL, FH) setting data 16 based on the determination result And a set frequency changing unit 20 that changes

<Circuit operation>
The circuit operation will be described.

  FIG. 2 is a flowchart for explaining image frequency avoidance processing executed in the control circuit 12 according to the present invention.

  In this example, an example of a control method for performing signal detection while avoiding the image frequency in the measurement of the overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency is shown.

  In step S1, the local frequency calculator 15 determines a local frequency Lo used for measurement of the overwrite characteristic.

  In step S <b> 2, using the image frequency calculation unit 18 and the image disturbance determination unit 19, the recording medium 102 falls within the frequency band calculated by the sum or difference between the determined local frequency Lo and the center frequency of the intermediate frequency filter 3. It is determined whether or not there is an image frequency having a frequency component capable of detecting a signal other than a known frequency component recorded using a predetermined overwrite frequency on the magnetic recording medium for hard disk.

  In step S3, if it is determined that an image frequency having a signal detectable frequency component other than the known frequency component recorded on the recording medium 102 exists in the calculated frequency band, the writing frequency (FL, FH) is calculated. The local frequency Lo is changed using the unit 17 and the set frequency changing unit 20 so that the frequency component of the image frequency is not detected.

  In this case, the change of the local frequency Lo may be set as follows.

  That is, when the image frequency matches the overwrite frequency, the local frequency Lo may be changed. Further, the local frequency Lo may be changed by the calculated frequency band to the low frequency side or the high frequency side of the overwrite frequency.

<Specific example>
Next, a specific example will be described.

  A method for avoiding the image interference signal by changing the local frequency Lo of the local frequency transmitter 6 will be described.

  Procedure 1) The local frequency Lo of the local signal is determined so that a desired measurement frequency is obtained.

  Procedure 2) Overwrite characteristic measurement frequency (usually the same as the first writing frequency) exists in image frequency ± [(intermediate frequency filter (IF filter) passband / 2) + α] calculated from local frequency Lo Judge whether to do. In this case, the matching is confirmed including the image frequency generated from the harmonics of the local frequency Lo.

Here, a calculation example of the image frequency is given.
Image frequency = (Lo × n) ± IF center frequency ± [(IF passband / 2) + α] (1)
(N is Lo harmonic order, α is guard band frequency width to prevent signal leakage into IF filter)

  Procedure 3) When the image frequency and the measurement frequency of the overwrite characteristic match in Procedure 2, the local frequency Lo set in Procedure 1 is switched to the reverse heterodyne side. However, when Lo = measurement frequency + IF, the opposite is set to Lo = measurement frequency−IF.

<Image interference signal avoidance method>
Next, the reason why the image interference signal can be avoided when the simple heterodyne circuit shown in FIG. 1 is used will be described with reference to FIGS. 3 and 4. FIG.

  When heterodyne is performed, image disturbance occurs (ie, image frequency exists). In this case, as a conventional measure, interference has been avoided by double (or triple) heterodyne.

  On the other hand, in the present invention, interference is avoided by switching (shifting) the local oscillation frequency so that the window of the image frequency remains at a frequency free of signal components while maintaining a circuit in which an image may enter. It is to do. This is because spectrum analyzers that analyze radio signals flying in the air do not know at which frequency the signal exists, so this method can not be taken, but in the media test, after erasing the signal of known frequency components Since writing is performed, the circuit configuration can be changed so that the image frequency window does not enter. According to this method, the circuit configuration can be greatly simplified. In addition, since the image frequency detects the signal at 0 dB with respect to the measurement frequency, there is a drawback that the medium noise component is measured in a form superimposed on the measurement signal.

  In other words, in the present invention, this method cannot be used in general frequency observation, but utilizes the characteristic of medium inspection and is unique.

  FIG. 3 shows an example of image disturbance in the heterodyne method.

  In this example, when an intermediate frequency filter having a center frequency of 10 MHz is used, the local oscillation frequency (local frequency Lo) is set 10 MHz below the frequency to be observed, and the frequency is converted to 10 MHz and observed. (50 MHz-40 MHz = 10 MHz).

  However, at the same time, the 30 MHz signal is also frequency-converted to 10 MHz (40 MHz-30 MHz = 10 MHz), so that the 50 MHz signal and the 30 MHz signal are measured with exactly the same sensitivity.

  Although it is free to use the sum signal with the frequency of the intermediate frequency filter 3 as the observation frequency or the difference signal as the observation frequency with respect to the local transmission frequency, the heterodyne frequency on the side not used for observation is defined as the image frequency. Call.

  FIG. 4 shows a method of image avoidance by changing the local transmission frequency according to the present invention.

  In this example, if a 30 MHz signal component is present on the recording medium 102, interference is caused, so the local oscillation frequency is set to the upper side by 10 MHz, which is an intermediate frequency of the frequency <50 MHz> to be observed. 50 MHz of the observation signal is (60 MHz−50 MHz = 10 MHz) and can be observed after being converted to 10 MHz.

  At this time, since the image frequency is 60 MHz + 10 MHz = 70 MHz, if the recording medium 101 does not contain a signal component of 70 MHz, there is no problem in observation.

  As described above, in the measurement of the recording medium 102, since the frequency component to be written in advance is known, this method can be avoided.

  Accordingly, since the inspection apparatus 100 including the control circuit 12 is configured as an overwrite characteristic measurement circuit, a circuit for countermeasures against image disturbance can be omitted in the measurement of the overwrite characteristic, and the apparatus cost can be reduced. be able to.

  In addition, since the circuit for measuring the image interference can be simplified by adopting a simplified heterodyne circuit configuration for the measurement circuit for the overwrite characteristic, the overwrite characteristic that has been performed in a device that assumes multiple channels. A complicated switch circuit for sharing the measurement circuit can be omitted.

  Further, the measurement speed can be improved by providing the control circuit 12 of the inspection apparatus 100 for each channel as a measurement circuit for the overwrite characteristic.

[Second example]
A second embodiment of the present invention will be described with reference to FIG. In addition, about the same part as the 1st example mentioned above, the description is abbreviate | omitted and the same code | symbol is attached | subjected.

  In this example, the content of the control process in the control circuit 12 of the inspection apparatus 100 of FIG. 1 of the first example described above is changed. The circuit configuration of the inspection apparatus 100 is the same as that in FIG. 1, and a description thereof is omitted here.

<Circuit operation>
The circuit operation will be described.

  FIG. 5 is a flowchart for explaining the image frequency avoidance processing executed in the control circuit 12 according to the present invention.

  In step S10, the local frequency calculator 15 determines a local frequency Lo used for measurement of the overwrite characteristic.

  In step S <b> 11, the recording medium 102 is included in a frequency band calculated by the sum or difference between the determined local frequency Lo and the center frequency of the intermediate frequency filter 3 using the image frequency calculation unit 18 and the image disturbance determination unit 19. It is determined whether or not there is an image frequency having a frequency component capable of detecting a signal other than a known frequency component recorded using a predetermined overwrite frequency on the magnetic recording medium for hard disk.

  In step S12, when it is determined that an image frequency having a signal detectable frequency component other than the known frequency component recorded on the recording medium 102 exists in the calculated frequency band, the writing frequency (FL, FH) is calculated. The writing frequency (FL, FH) for measurement used for measurement of the overwrite characteristic is changed so that the frequency component of the image frequency is not detected using the unit 17 and the set frequency changing unit 20.

  In this case, the change of the writing frequency for measurement (FL, FH) may be set as follows.

  That is, when the image frequency matches the overwrite frequency, the write frequency (FL, FH) may be changed. In addition, the writing frequency (FL, FH) is changed within the measurable frequency range of the overwrite characteristic, and is changed by the pass band width of the intermediate frequency filter 3 to the low frequency side or the high frequency side of the overwrite frequency. You may make it do.

<Specific example>
Next, a specific example will be described.

  A method for avoiding the image interference signal by changing the measurement writing frequency (FL, FH) as the measurement frequency will be described.

  Procedure 4) When the change is made in the procedure 3 in the method for avoiding the image interference signal in the first example, the image frequency is again calculated from the local frequency Lo ± [(IF passband / 2) + α]. Determine whether there is a measurement frequency for the overwrite characteristics.

  Step 5) If it is determined that the measurement frequency matches the image frequency, either one or both of the two writing frequencies (FL and FH) for the measurement of the overwrite characteristic are passed through the intermediate frequency filter 3. Change to the + side or-side by the bandwidth.

  Procedure 6) By performing the procedure 1 of the first example described above, the image frequency does not exist within the measurement frequency band of the overwrite characteristic, and image interference can be avoided.

  Procedure 7) The change of the writing frequency for measurement is a minute frequency of about 100 KHz and hardly affects the overwrite characteristics.

<Image interference signal avoidance method>
Next, the reason why the image interference signal can be avoided when the simple heterodyne circuit of FIG. 1 is used will be described.

  In this example, an image avoidance method by changing the measurement frequency according to the present invention is shown.

  In the example of FIG. 3 described above, when the disturbing frequency component is 30 MHz, for example, when the observation frequency is changed to 52 MHz, the image frequency becomes 32 MHz, and the passband width of the intermediate frequency filter 3 (usually about 100 KHz in overwriting). If there is no 30MHz signal in the), there will be no problem in measurement.

  Since it is known in advance whether the inspection frequency (or its harmonics) matches the image frequency when setting the overwrite writing frequency, the control circuit 12 of the inspection apparatus 100 sets the alarm setting to avoid this match. By doing so, it is possible to configure and measure in a simple circuit as a measurement circuit for the overwrite characteristics.

It is a block diagram which shows the structure of the test | inspection apparatus for avoiding an image disturbance signal which is the 1st Embodiment of this invention. It is a flowchart which shows the process which avoids an image frequency by the change of the local frequency performed in the control circuit which concerns on this invention. It is explanatory drawing which shows the example of the image disturbance in a heterodyne system. It is explanatory drawing which shows the method of the image avoidance by the change of a local frequency. It is a flowchart which shows the process which avoids an image frequency by the change of the write-in frequency for a measurement performed in the control circuit which is the 2nd Embodiment of this invention.

Explanation of symbols

1 Measurement signal 2 Mixer 3 Intermediate frequency filter (IF filter)
4 Amplitude detector 5 Local signal 6 Local frequency transmitter 7 Write signal 8 Write frequency transmitter 9 Head control circuit 10 Read / write head unit 11 Frequency setting circuit 12 Control circuit 13 Measurement frequency setting data 14 Local frequency setting data 15 Local frequency Calculation unit 16 Write frequency (FL, FH) setting data 17 Write frequency (FL, FH) calculation unit 18 Image frequency calculation unit 19 Image interference determination unit 20 Set frequency change unit 100 Inspection device 101 Read signal amplification circuit 102 Recording medium

Claims (13)

A control method for performing signal detection while avoiding an image frequency in measurement of an overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency,
Determining a local frequency used for measurement of the overwrite characteristic;
Signals other than known frequency components recorded on the recording medium using the predetermined overwrite frequency within a frequency band calculated by the sum or difference between the determined local frequency and the center frequency of the intermediate frequency filter Determining whether there is an image frequency having a detectable frequency component;
When there is an image frequency having a signal detectable frequency component other than the known frequency component recorded on the recording medium in the calculated frequency band, the frequency component of the image frequency is not detected. A control method comprising a step of changing a local frequency. The step of changing includes
The control method according to claim 1, further comprising: changing the local frequency when the image frequency matches the overwrite frequency. The step of changing includes
The control method according to claim 1, further comprising a step of changing the local frequency by the calculated frequency band to a low frequency side or a high frequency side of the overwrite frequency. A control method for performing signal detection while avoiding an image frequency in measurement of an overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency,
Determining a local frequency used for measurement of the overwrite characteristic;
Signals other than known frequency components recorded on the recording medium using the predetermined overwrite frequency within a frequency band calculated by the sum or difference between the determined local frequency and the center frequency of the intermediate frequency filter Determining whether there is an image frequency having a detectable frequency component;
When there is an image frequency having a signal detectable frequency component other than the known frequency component recorded on the recording medium in the calculated frequency band, the frequency component of the image frequency is not detected. And a step of changing a measurement write frequency used for measurement of the overwrite characteristic. The step of changing includes
The control method according to claim 4, further comprising a step of changing the measurement write frequency when the image frequency matches the overwrite frequency. The step of changing includes
The step of changing the write frequency for measurement within the measurable frequency range of the overwrite characteristic, and changing the overwrite frequency to the low frequency side or the high frequency side by the pass bandwidth of the intermediate frequency filter The control method according to claim 4, further comprising: A computer-readable recording medium with a computer program having a method capable of executing instructions according to more請 Motomeko 1 to 6 either to the computer. A control device for performing signal detection while avoiding an image frequency in measurement of an overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency,
Means for determining a local frequency used for measurement of the overwrite characteristic;
Signals other than known frequency components recorded on the recording medium using the predetermined overwrite frequency within a frequency band calculated by the sum or difference between the determined local frequency and the center frequency of the intermediate frequency filter Means for determining whether there is an image frequency having a detectable frequency component;
When there is an image frequency having a signal detectable frequency component other than the known frequency component recorded on the recording medium in the calculated frequency band, the frequency component of the image frequency is not detected. A control device comprising means for changing a local frequency. The means for changing is
9. The control apparatus according to claim 8, further comprising means for changing the local frequency when the image frequency matches the overwrite frequency. The means for changing is
10. The control apparatus according to claim 8, further comprising means for changing the local frequency by the calculated frequency band to a low frequency side or a high frequency side of the overwrite frequency. A control device for performing signal detection while avoiding an image frequency in measurement of an overwrite characteristic for a recording medium overwritten using a predetermined overwrite frequency,
Means for determining a local frequency used for measurement of the overwrite characteristic;
Signals other than known frequency components recorded on the recording medium using the predetermined overwrite frequency within a frequency band calculated by the sum or difference between the determined local frequency and the center frequency of the intermediate frequency filter Means for determining whether there is an image frequency having a detectable frequency component;
When there is an image frequency having a signal detectable frequency component other than the known frequency component recorded on the recording medium in the calculated frequency band, the frequency component of the image frequency is not detected. A control device comprising means for changing a measurement write frequency used for measurement of an overwrite characteristic. The means for changing is
12. The control apparatus according to claim 11, further comprising means for changing the measurement write frequency when the image frequency matches the overwrite frequency. The means for changing is
Means for changing the write frequency for measurement within the measurable frequency range of the overwrite characteristic, and changing the overwrite frequency to the low frequency side or the high frequency side by the pass band width of the intermediate frequency filter The control device according to claim 11, comprising:

Images