Oscilloscopes: Bandwidth or Brand Name

Discussion in 'General Electronics Chat' started by Sal Ammoniac, Jul 31, 2014.

  1. Sal Ammoniac

    Thread Starter New Member

    Jun 30, 2010
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    Good test equipment isn't cheap, and there's always trade-offs involved.

    Would it be better to get an off-brand oscilloscope, such as a Rigol, with higher bandwidth, or spend the same money and get a brand name, such as Agilent or Tek with lower bandwidth?

    For example, I can get a 350 MHz (or even a 500 MHz) scope from Rigol for roughly the same price as a 200 MHz Agilent or Tek scope.
     
  2. tindel

    Active Member

    Sep 16, 2012
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    Both... Buy used
     
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Most people don't need bandwidth. How often do you need to inspect a 200MHz signal?
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
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    Good used test equipment is cheap (at least in the US). EBay is flooded with great test equipment and excellent prices. If you are patient you can get incredible deals.

    Now is the time to fill your lab with good used test equipment.
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    I have never had a need for anything above 100MHz, hence 200MHz would be fine with me.
     
  6. Sensacell

    Well-Known Member

    Jun 19, 2012
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    Buy the best brands, Tek, HP, etc. USED- you can usually re-sell them for what you paid.

    And then you get to enjoy real quality pro gear!
     
  7. Sal Ammoniac

    Thread Starter New Member

    Jun 30, 2010
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    Not often, but the general rule of thumb is that you need bandwidth of about 5x the speed of the fastest digital signal you're inspecting. So a 200 MHz scope is good up to about 40 MHz.

    Digital signals are square waves, and square waves consist of a fundamental frequency and all odd harmonics. To see a reasonable representation of the true shape of a digital signal on a scope, you need to see up to at least the 5th harmonic, hence the 5x rule of thumb cited above.

    Another way to look at it is to consider the rise time of the signal. This is related to the scope bandwidth required by roughly 0.35/rt, where "rt" is the rise time in seconds. Applying this rule, a signal with a 1 ns rise time requires 350 MHz of scope bandwidth.

    Things are more complex than this, actually, but you get the general idea.
     
  8. MrChips

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    Oct 2, 2009
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    Ok, if you say so. Then you have convinced yourself to go for bandwidth.
     
  9. AlphaDesign888

    New Member

    Jul 27, 2014
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    He's right. I have read an textbook that states something like x5
    But that was for an CRO. Not an DSO!
     
  10. Lestraveled

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    May 19, 2014
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    The other side of this discussion is a digital verses analog oscilloscope. Digital scopes are great at showing events that happen in between long intervals of time.... or only once. Analog scopes are great for reoccurring events at high frequency. Both are important tools.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    The bandwidth requirement doesn't change if you go from an analog to a digital scope.
     
  12. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Connections, probes etc are very important at higher bandwidth.

    Cheap scopes may only quote the bandwidth of the y amp, not the whole instrument.

    Particularly if you are doing digital work then triggering, screen size, multiple traces, cursors etc are also important considerations.

    It is often difficult to get stable displays on cheap scopes at high frequencies for the above reasons.
     
  13. alfacliff

    Well-Known Member

    Dec 13, 2013
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    I have a tec 7633 dual beam storeage scope. a 100 mhz chasis, with two quad trace vertical modules installed. one advantage of these is that there are quite a few imput modules and sweep modules available,from differential to spectrum analyzer inputs. the storeage feature is nice too, sometimes.
     
  14. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I own a Hantek DSO-2250 200 Mhz usb scope and it's affordable, reliable and gets the job done. I think it's far better to have a pc controlled osc instead of a standalone one, plus it's a lot cheaper.
    Look for them in Amazon, they've got reasonable prices
     
  15. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    What makes you think Rigol is an "off-brand" scope? Rigol makes some excellent equipment.
     
  16. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    I'm afraid I'd have to disagree. USB scopes are rarely worth the money unless you're just a hobbyist and only want to see, say, the square wave from a 555 timer. But for sheer precision, bandwidth, and overall quality, USB scopes will not cut it.
     
  17. RobeeJ

    New Member

    Mar 19, 2013
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    Not to mention the fact that just from a usability perspective, you can't beat knobs and buttons. :)
     
    DerStrom8 likes this.
  18. Sal Ammoniac

    Thread Starter New Member

    Jun 30, 2010
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    It's just that I consider any scope that's not a Tek or an Agilent scope as off-brand.

    As an American, Tek in particular has been the brand of scope for decades, and HP/Agilent has too, to a slightly lesser extent. Just like when I think of multimeters, there's Fluke, and everything else is off-brand.
     
  19. tom_s

    Member

    Jun 27, 2014
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    thanks for this, was wondering whether to spend money on one, think i'll stick to the trio 15MHz dual trace. (pushing about 35 years now)
     
    Last edited: Aug 2, 2014
  20. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Well, yes... there are scopes, and then there are scopes... I use mine for digital circuits that never work at more than 32 Mhz...
    For telecommunications one would need a scope in the Ghz range, for instance... I guess it all depends on the use...
     
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