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OK to use Fluke 77 for MDS measurement?

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  • ve7vv
    For the ARRL method of measuring MDS, one needs to measure the RMS voltage at the output of a 500 Hz wide filter (e.g. 200 to 700 Hz), with and without a
    Message 1 of 6 , Jul 10, 2014
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      For the ARRL method of measuring MDS, one needs to measure the RMS voltage at the output of a 500 Hz wide filter (e.g. 200 to 700 Hz), with and without a signal. My Fluke 77 digital multimeter manual says the AC voltage scale is good to 1000 Hz - I presume Fluke means this for a pure sine wave. Does it also apply for white noise and for white noise plus a sine wave? If so, can i use the Fluke 77 for a measurement of minimum detectable signal on my Ensemble II by putting the Fluke on the headphone output after setting up a 500 Hz CW filter and turning off AGC?


    • cc_photo
      Better way is use an analog scope. ccphoto
      Message 2 of 6 , Jul 11, 2014
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        Better way is use an analog scope.

        ccphoto
      • Paul Playford
        Not true. You are looking for RMS voltage and an oscilloscope is not the best for RMS readings. I use a like my H-P 400E. Paul, W8AEF From:
        Message 3 of 6 , Jul 11, 2014
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          Not true.  You are looking for RMS voltage and an oscilloscope is not the best for RMS readings.
           
          I use a like my H-P 400E.
           
          Paul, W8AEF
           
          Sent: Friday, July 11, 2014 8:16 AM
          Subject: [softrock40] Re: OK to use Fluke 77 for MDS measurement?
           
           

          Better way is use an analog scope.

          ccphoto

        • Jean-Paul Louis
          If you have a pure sine wave, the relationship between Peak to Peak value and RMS value is known, so a scope can be used. If the signal is complex, the scope
          Message 4 of 6 , Jul 11, 2014
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            If you have a pure sine wave, the relationship between Peak to Peak value and RMS value is known, so a scope can be used.
            If the signal is complex, the scope has no value at all.
            Analog versus Digital is irrelevant, but digital scopes have often math functions that include RMS calculations.

            my $0.02,

            Jean-Paul
            AC9GH


            On Jul 11, 2014, at 11:35 AM, 'Paul Playford' w8aef@... [softrock40] <softrock40@yahoogroups.com> wrote:

            >
            > Not true. You are looking for RMS voltage and an oscilloscope is not the best for RMS readings.
            >
            > I use a like my H-P 400E.
            >
            > Paul, W8AEF
            >
            > From: mailto:softrock40@yahoogroups.com
            > Sent: Friday, July 11, 2014 8:16 AM
            > To: softrock40@yahoogroups.com
            > Subject: [softrock40] Re: OK to use Fluke 77 for MDS measurement?
            >
            >
            > Better way is use an analog scope.
            >
            > ccphoto
            >
            >
            >
          • Paul Playford
            The original objective is to measure MDS. The first value will be noise, the second value will be noise + 3dB. Paul, W8AEF ... From: Jean-Paul Louis
            Message 5 of 6 , Jul 11, 2014
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              The original objective is to measure MDS. The first value will be noise,
              the second value will be noise + 3dB.

              Paul, W8AEF

              -----Original Message-----
              From: Jean-Paul Louis louijp@... [softrock40]
              Sent: Friday, July 11, 2014 9:02 AM
              To: softrock40@yahoogroups.com
              Subject: Re: [softrock40] OK to use Fluke 77 for MDS measurement?

              If you have a pure sine wave, the relationship between Peak to Peak value
              and RMS value is known, so a scope can be used.
              If the signal is complex, the scope has no value at all.
              Analog versus Digital is irrelevant, but digital scopes have often math
              functions that include RMS calculations.

              my $0.02,

              Jean-Paul
              AC9GH


              On Jul 11, 2014, at 11:35 AM, 'Paul Playford' w8aef@... [softrock40]
              <softrock40@yahoogroups.com> wrote:

              >
              > Not true. You are looking for RMS voltage and an oscilloscope is not the
              > best for RMS readings.
              >
              > I use a like my H-P 400E.
              >
              > Paul, W8AEF
              >
              > From: mailto:softrock40@yahoogroups.com
              > Sent: Friday, July 11, 2014 8:16 AM
              > To: softrock40@yahoogroups.com
              > Subject: [softrock40] Re: OK to use Fluke 77 for MDS measurement?
              >
              >
              > Better way is use an analog scope.
              >
              > ccphoto
              >
              >
              >



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            • warrenallgyer
              Your Fluke 77 will work fine for MDS measurements. Use the AC Volts scale and measure the noise on the speaker terminals. Set a convenient level for the ears
              Message 6 of 6 , Jul 11, 2014
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                Your Fluke 77 will work fine for MDS measurements. Use the AC Volts scale and measure the noise on the speaker terminals. Set a convenient level for the ears and the meter with the audio gain control. Then, touching nothing else, add signal until the reading increases by 1.4 x. In other words, if the noise only was reading 1 volt, then the noise + signal level would be 1.4 volts at MDS.

                Warren Allgyer
                9V1TD
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