o scope bandwidth

Discussion in 'General Electronics Chat' started by DexterMccoy, Apr 4, 2014.

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  1. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    Why is it hard for low bandwidth O scopes to Trigger very low frequency waveforms?

    When I'm using a 60Mhz O scope, the trigger is in Auto mode, won't trigger low frequencys waveforms, the low frequency waveforms will be FREE RUNNING

    But when I use a 150Mhz O scope , the trigger is in Auto Mode, it will trigger low frequency waveforms

    why does the 150Mhz O scope trigger low frequency waveforms and not the 60Mhz?
     
  2. w2aew

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    Jan 3, 2012
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    Check the signal and trigger coupling settings. You may need to use DC coupling on the trigger settings.
     
  3. DexterMccoy

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    Feb 19, 2014
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    I tried it, it won't keep a stable waveform in AUTO MODE

    I am measuring low frequencys 1hz and below

    In AUTO MODE the low frequencys are just free running

    But they do sync only using a 150MHz O scope in AUTO MODE

    I'm not sure why low frequencies trigger sync using a 150MHZ and not a 60Mhz in auto mode

    any reason why?
     
  4. w2aew

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    Different scopes will differ in how long the AUTO trigger mode "waits" until it automatically sends the sweep. Try using the Normal trigger mode.

    AUTO trigger does not automatically setup the trigger. It only sends a sweep automatically if a valid trigger event is detected in some time period (which varies between scope models).
     
  5. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    What cause it to do the Waiting? is this the pre trigger delay?

    Yes in Normal trigger mode it works, but you have to fine tune the triggers knobs

    But other O scopes you can just use the AutoTrigger if the MHZ is higher, why is that?

    Yes i Know that


    Why does O scope have a hard time detecting a trigger event for Low frequencies? it will just be free running in automode , but in normal mode you have to fine tune the trigger knob to detect it

    Also the higher the O scopes MHZ, in automode it detects a trigger event for a time period better? why is that?
     
  6. w2aew

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    It's part of the design of the scope's trigger circuit. Generally, you have no control over it.

    Exactly right. This is the way it's supposed to work.
    It has nothing to do with the scope BW. It's just a difference in the AUTO trigger time-out between the two scopes.

    The scope isn't having a hard time detecting a trigger. It's just that the trigger hasn't occurred before the AUTO-trig timeout expired on that scope. It sounds like the AUTO trigger timeout is longer on your higher BW scope, so an actual trigger is occurring before the timeout expires.
     
  7. DexterMccoy

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    Feb 19, 2014
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    What do you mean by this Time out? or trigger time out?

    Do you mean the trigger circuit samples the pulse period?

    Longer? meaning? it's sampling the pulse period?
     
  8. w2aew

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    AUTO trigger works by waiting for a trigger event to occur, but if a trigger event doesn't occur with a predescribed time period, it initiates a trigger on its own. When I said "timeout", I'm referring to this predescribed time period.

    If an actual trigger occurs before this time period expires, then this actual trigger is used. If an actual trigger doesn't occur before this time period is up, then the circuit initiates its own trigger and your signal appears untriggered.

    For very low repetition rate signals, it is very common that you would have to turn off the AUTO trigger mode and use Normal trigger.

    Here's my video on AUTO triggering
    http://www.youtube.com/watch?v=BKjJK1rsZmM
     
  9. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    The Trigger Event would be what?

    A Pulse train has what trigger events? it can occur on the positive edge or negative edge

    But a Pulse Train has a Time period , which is the Predescribed time period or time out?

    Does a pulse train have a trigger event? or how do you know when a pulse train signal doesn't have a trigger event?


    Why is it very common? what is the auto mode triggering circuits problems or flaws it has? that normal mode has?

    It seems that the Normal mode trigger circuit has something built in that is different than the Auto trigger modes circuits

    True, but low frequency's are slower speed/rate so the trigger event should be easier i would think

    But it seems that O scope have a hard time to detect a trigger event on low frequency pulse trains signals because of the Time period of the low frequency?
     
  10. Little Ghostman

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    Jan 1, 2014
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    Get real your asking questions for the sake of asking, The trigger EVENT is obviously the point at which the signal rises above the level you set the trigger for, OR if you have a smart trigger whatever sequence you have set!

    Most of what you ask you could answer if you stopped and thought about it. For someone that works in electronics the fact you have no idea what triggers a scope is a worry. The Guy helping you is the one that made the video SCOPES FOR DOPES, I gave you the link on ETO, you said you had watched all 2 hours of it, you also said it didnt answer your question's. I know for a fact if you had bothered to actually watch it you would know the answer to most the nonsense your asking.
    Let me guess your posting this trigger question because no one is playing in your other threads, so its time for a new batch??

    Yes sorry mods but enough is enough.

    Oh and before you start shouting at me to stay out of your threads, think about this.
    You say you dont post in my threads, that is correct, the fact is you dont post in anyone's threads! This is a community and yet you refuse to post any form of help to anyone. All you want is to take by asking nonsense and give nothing back. I bet your even surprised to be banned from more forums than any other person known to man.

    LG
     
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  11. Brevor

    Active Member

    Apr 9, 2011
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    Beware of the Wee Ghostman !

    I wish everyone would stay out of his threads.
     
  12. Little Ghostman

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    Jan 1, 2014
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    Yes but I was wrong to ave a go! I was just annoyed that a question like that was asked.
    Maybe Alan could do a Scopes for Dopes II video, aimed at the lobotomized brain dead, if he assumes his audience is politicians then that should be just about the right level :D
     
  13. shortbus

    AAC Fanatic!

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    Amen brother LG. But would you really want him helping you? :)
     
  14. w2aew

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    Jan 3, 2012
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    The trigger event is something that YOU setup in the scope, based on your input signal. You can set the scope to trigger on the rising edge or falling edge, for example. Here is a video you can watch to better understand the trigger controls:
    http://www.youtube.com/watch?v=OFGm-Pel4Hg


    There isn't a flaw in the auto trigger mode, this is just the way it works. If it doesn't see a trigger in a few hundred milliseconds, it sends the sweep on it's own. Different scopes will 'wait' a different amount of time before automatically sending the trace on its own. If your signal doesn't have a trigger event often enough, then the auto trigger sends the trace. I don't know how to describe this any simpler. Again, review this video on AUTO triggering:
    http://www.youtube.com/watch?v=BKjJK1rsZmM

    They are the SAME circuit - nothing different. The trigger circuit is looking for a trigger event as defined by your controls. In Normal mode, it waits indefinitely for the trigger to happen. In AUTO mode, it only waits for a few hundred milliseconds and sends a trace anyway, then waits again....


    The scope is having NO PROBLEM seeing your trigger - you proved it when you said that it works in Normal trigger mode.

    The time period of your signal is TOO SLOW to use the AUTO trigger mode on one your scopes. Simple as that. I don't think I can make this any simpler.
     
  15. Little Ghostman

    Member

    Jan 1, 2014
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    Lucky enough I think I can
    01010100 01101000 01100101 00100000 01110100 01101001 01101101 01100101 00100000 01110000 01100101 01110010 01101001 01101111 01100100 00100000 01101111 01100110 00100000 01111001 01101111 01110101 01110010 00100000 01110011 01101001 01100111 01101110 01100001 01101100 00100000 01101001 01110011 00100000 01010100 01001111 01001111 00100000 01010011 01001100 01001111 01010111 00100000 01110100 01101111 00100000 01110101 01110011 01100101 00100000 01110100 01101000 01100101 00100000 001000001 01010101 01010100 01001111 00100000 01110100 01110010 01101001 01100111 01100111 01100101 01110010 00100000 01101101 01101111 01100100 01100101 00100000 01101111 01101110 00100000 01101111 01101110 01100101 00100000 01111001 01101111 01110101 01110010 00100000 01110011 01100011 01101111 01110000 01100101


    There you go, explained in binary! As far as I know Binary is as simple as it gets
     
  16. Little Ghostman

    Member

    Jan 1, 2014
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    although it could probably be expressed as,
    01101001 01110100 01110011 00100000 01100010 01100101 01100011 01100001 01110101 01110011 01100101 00100000 01111001 01101111 01110101 01110010 00100000 01110011 01110100 01110101 01110000 01101001 01100100
     
  17. MrChips

    Moderator

    Oct 2, 2009
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    Everything should be made as simple as possible, but not too simple. - Albert Einstein
     
  18. Little Ghostman

    Member

    Jan 1, 2014
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    Ok sorry, point taken :D
     
  19. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
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    Mr. Chips , i think Little Ghostman has spammed my thread and has crossed the line way to many times in my threads, when is it time for the mods to step in and stop the harassment and spamming in my threads?

    I'm trying to have a conversation with w2aew , which has been very helpful to me

    I don't need shortbus or littleghostman ever in my threads anymore to give their negative comments
     
    shortbus likes this.
  20. DexterMccoy

    Thread Starter New Member

    Feb 19, 2014
    429
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    Yes I know this, but my question is why can't an O-scope trigger off of the trigger event off of low frequencies? in automode?

    So the Trigger circuit internally inside the O-scope are different, because some have a longer wait time before automatically sending the trace on it's own

    When looking at a schematic of the triggering circuit in the O-scope , what is determining the wait time?

    The Predelay triggerin is something else? this is not the wait time?

    I'm confused on how the Wait time circuit works internally inside the triggering circuit in the O-scope

    The Wait Time circuit
    1.) a sample and hold circuit?
    2.) a delay circuit?
    3.) a sampling circuit?
    4.) what is it?

    So other O-scopes wait times differ? some are a hundred milliseconds, other O scopes are long milliseconds

    My question is , why does an O-scope need a "Longer wait time" for Low frequencys?

    So the Auto trigger mode needs a Longer wait time for low frequencys? but why does it need a longer wait time?

    It doesn't make sense to me as to why
     
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