Mark and Space Ratio for Pulse width modulation

Discussion in 'General Electronics Chat' started by LeoWilson, Oct 4, 2014.

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  1. LeoWilson

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    Why does tech use Mark & Space Ratio for Pulse width modulation measurements?

    When does a tech measure the mark & space time duration for what type of circuits or applications?
     
  2. Papabravo

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    Your question does not make much sense to me. Could you elaborate?
     
  3. #12

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    Could this be a homework question where you know the background because you just read the chapter, but we didn't?
     
  4. jpanhalt

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  5. LeoWilson

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    Oct 3, 2014
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  6. LeoWilson

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    What is the advantage of measuring pulse trains waveforms using mark & space measurements compared to duty cycle, time period, pulse width?

    What circuits or applications do you measure using Mark & Space ratios? for TTL or CMOS circuits?
     
  7. LeoWilson

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    As a Tech, I have only measured for TTL and CMOS circuits is the time period, pulse width, duty cycle.

    When would I want to measure a TTL or CMOS waveform and use the mark & space ratio? when is this used and what is it used for?
     
  8. nsaspook

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    Mark & space measurements are used in transmission circuits to check for modulation distortion of digital signals.
     
  9. LeoWilson

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    But why do they use Mark and space measurements?

    How does mark and space measurement tell the modulation distortion? i'm guessing pulse width, time period, duty cycle doesn't check for the modulation distortion of why is that?

    Doesn't the time period, pulse width, duty cycle already give the same results or is it different and how so?

    I'm new to this mark & space measurements, i'm not sure what it really is and how it's different and when it's used and why it's used
     
  10. nsaspook

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    It's just an old name for modern digital parameters that dates back to sending Morse code. In RTTY the digital signal is transmitted by shifting the carrier by a fixed amount up or down from the carrier (FSK). These shifts are called Mark & Spaces that in a perfect world would have a 0% bias distortion if a perfect square wave (50% duty cycle) was sent. When information is sent in the form of digital codes mark & space measurements check to be sure that proper timing is present on the signal. So if we sent that signal in a circuit that had some type of distortion the duty cycle could change from 50% to some value that favored marks or spaces creating what's call a bias that would cause printing errors on the old mechanical teletype machines when sending real codes. For the long-range HF links I setup and worked in the Navy as a Technical Controller almost 40 years ago this was usually caused by skip or ionospheric conditions what affected the delay or signal strength of received signals at slightly different frequencies.

    To fix the problem we normally used a regenerator until we moved the circuit to another channel.
    http://www.hypertools.com/dovetron/Dovetron_MPC-1000CR.pdf
     
    Last edited: Oct 4, 2014
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  11. Papabravo

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    This whole thread is a big red herring. They amount to the same thing and one can be expressed in terms of the other. So why are you obsessing about this? There is no there there!
    For example 50% duty cycle is identical to a mark space ratio of 1:1
    Again what's the big deal?
     
  12. LeoWilson

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    Oct 3, 2014
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    Yes true, but it seems that mark space ratio measurements are used to modulation waveforms, AM and FM modulation , phase modulation, modulation distortion , pulse width modulation

    When I measure pulse width modulation waveforms, i just measure the time period, pulse width, duty cycle

    I have never measured the mark and space ratio , and i'm not sure what it is used for and why would i want to use it?
     
  13. Papabravo

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    I'm sure you'll tell us if you ever figure it out.

    Good Luck
     
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