Frequency Measurement - Oscilloscope

Discussion in 'General Electronics Chat' started by Mazaag, Sep 24, 2007.

  1. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
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    0
    Hey guys,

    I'm working with a Trektronics digitl oscilloscope to measure the frequency content of some signal.. I was wondering if someone can give me a DSP explanation as to what settings I require in order to avoid aliasing..

    lets say that i am interested in measuring the frequency content at 100Hz.. what do I have to set the time base to be (or the sampling rate) ? and how does it relate to the samples per second of the oscilloscope...

    I hope my question is clear...


    Thanks guys
     
  2. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Given that example, the time base would be 1/100s. The period of a signal, measured in seconds, is the inverse of it's frequency.
     
  3. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
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    ..but doesn't the sampling rate have to be atleast twice the frequency of interest? Thats as far as I know..but my question relates to the connection of the time base to the sampling rate of the actual oscilloscope...how can I determine the actual sampling rate used by the oscilloscope (which ii'm assuming is related to the time base setting)
     
  4. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Indeed, the sampling rate would be at least twice the frequency of interest, so you could make a better visual analysis. I don't know your model, but the models I knew would auto sync with the signal. The only thing I did was adjusting the coarse frequency.
     
  5. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
    255
    0
    the idea is that I have low frequency content that I would like to detect, so I wanted to know what to set the time base setting to in order to detect such components....

    the model i'm using is a Tektronix TDS2004... it says that it has a Sampling Rate of 1.0 GS/s.. (with a bandwidth of 60Mhz.) now i'm assuming that is the maximum rate that it could sample at... is that correct?

    It also says that the Record Length is 2.5K points on all time-bases... I have no idea what that means...

    There is also a possibility to use different types of windows.. ( Rectangular, Hanning , Flat-top)

    How do all these (Sampling Rate, Record Length, Window type) relate to each other and to measuring a specific frequency of interest...?

    Thanks guys
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Ah, the joys of DSO's. You might want to look on the web to see if you can scare up a manual for the beast, if you haven't got one.

    I have not used that beast, but they are prone to aliasing. You might practice on a known waveform, like the output of a function generator to see if the reproduction on the screen resembles the signal.
     
  7. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    It means that it will only give you 2500 data points per file-- limits your "recording" time.
     
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