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Low-cost oscilloscope recommendations

Discussion in 'Electronic Basics' started by joshc, Oct 27, 2005.

  1. joshc

    joshc Guest

    Hi,

    I haven't been able to find a recent thread on this so I figured I'd
    start a new one. I graduated with my M.S. in computer engineering a
    little over a year ago and have been working in the embedded systems
    world. My focus in school was real-time embedded software and the
    hardware courses I took had to do with computer architecture, one
    signals & systems course, digital system design using FPGAs and micros,
    and digital hardware design at the logic gate level.

    Now that I'm in industry I am working to strengthen my electrical
    engineering skills and playing with different circuits interfacing
    analog components to microprocessors/microcontrollers. I'd like to
    purchase my first oscilloscope so I can use it while I play around with
    circuits in my little home lab setup. It seems that a scope with a 100
    MHz bandwidth should be plenty for me but I'm not too sure since I've
    been reading up on trying to clarify what this really means. I'm not
    entirely clear on the concept of vertical amplifier bandwidth yet since
    it has to do with its frequency response and how much the input signal
    is attenuated and apparently the bandwidth rating for the scope is
    based on a -3 db attenuation or something.

    So I'd love some help from you guys on choosing what oscilloscope to
    purchase given my background above and what I'm looking to do. I've
    been spoiled by my college and work oscilloscopes which are high end
    tektronix and fluke scopes but obviously I can't afford those. I'm
    looking for something ideally around $300 but if I have to I can go up
    to about $500 so based on my research it seems this would limit me to a
    used, analog oscope. I've read a lot about the tektronix 465 scope so
    maybe that's the right one for me but I'm looking for suggestions on
    what oscilloscope you recommend as well as where you recommend buying
    it from. For a beginner like myself it seems that buying a used one
    from ebay might not be such a great idea since there is no guarantee
    the scope works and I wouldn't know how to fix it.

    Sorry for the long post but I'd like to give you as much information as
    I can so you expert folks can help me make the right choice. Please
    feel free to ask followup questions of me.

    Thanks for your time and help,

    Josh
     
  2. mike

    mike Guest

    Don't overlook obvious freebies.
    Convince your boss that it's in his best interest for you to learn more.
    They may have something gathering dust that you can borrow.

    Go find a ham radio club. Those guys often have spare scopes for their
    spare scopes in the basement. I have a spare TDS-540, if you can
    believe that insanity...
    mike

    --
    Wanted, Serial cable for Dell Axim X5 PDA.
    Return address is VALID but some sites block emails
    with links. Delete this sig when replying.
    FS 500MHz Tek DSOscilloscope TDS540 Make Offer
    Bunch of stuff For Sale and Wanted at the link below.
    MAKE THE OBVIOUS CHANGES TO THE LINK
    ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/
     
  3. Tim Williams

    Tim Williams Guest

    Tek 465/475/485s are cheap and plentiful on eBay, IIRC.

    Tim
     
  4. joshc

    joshc Guest

    Thanks for the recommendations. The problem with eBay is that almost
    all of the 465s have no warranty/guarantee that they work although the
    seller says they do. If I paid $300 and got a dud I'd lose my money
    since I don't have a clue how to repair them. Any idea of any online
    stores selling used test equipment?

    I'll look into the ham radio club thing since I've heard that before
    but have no clue what a "ham radio club" is and if I have any near me.

    Thanks.
     
  5. Noway2

    Noway2 Guest

    There are some on-line sellers of used test equipment, google for that
    phrase or for "used oscilloscopes" and you should come up with plenty.
    Ebay, however very well may be your best bet, though I do understand
    your concerns. Honestly, I don't feel that giving someone a "bad
    review" to be sufficient response to taking my money on a dud. While
    it would be possible to sue them, it would likely cost just as much.
    On the other hand, I know people who buy used test equip on ebay and
    they haven't had a bit of trouble.

    A word of caution against a 100 Mhz scope: You are on the right track
    about bandwidth limitations. The scope bandwidth will significantly
    influence your ability to see higher frequency signals. Modern digital
    electronics have very fast rise and fall times, which correspond to
    significant engergy in the higher harmonics. In order to acurately
    view these signals you need a scope with significant bandwidth. The
    high speed / high frequency nature of these signals is independant of
    the clock frequency of your circuit, meaning that a simple and - or
    circuit implemented with LSI chips coiuld exhibit this behavior and
    FPGAs, which you mention using above, tend to have 'very fast'
    transition times. A digital scope would also be beneficial with
    regards to catching and non-periodic and non repeating signals which
    are quite common in digital circuits.

    One thing to keep in mind is that I understand a lot of companies sell
    their outdated equipment on ebay when they are upgrading. What may be
    outdated for them could be a treasure for you.
     
  6. mike

    mike Guest

    I don't recall ever buying a scope that worked 100%. And it's not
    always obvious. Most have been easy to fix if you know what you're
    doing...and you spent 20 years working for TEK. The bad news is that
    it's really hard to fix a scope without a scope ;-(

    If you buy used, try to get manuals and probes. It's not unusual for
    a manual to cost more than the equipment did.

    Dealers can charge you 10X what it would cost to buy it right
    from an individual. There's a well-known test equipment refurbisher
    who sells equipment on ebay under an individual user name. "AS-IS No way
    to test it". I'd shy away from them, cause they damn sure can test it.
    Go here:
    http://www.qrz.com/i/names.html
    Type in your city and call one of 'em up and ask about clubs, people who
    might have scopes for sale etc. The whole objective of the hobby is to
    talk to people you don't know. They'll be glad to hear from you. Once
    they get to talking, you'll probably find it hard to shut 'em up... 3
    or 4 calls and you'll have a scope...depending on where you live.

    Put a request on rec.radio.amateur.equipment
    and
    sci.electronics.equipment
    and
    craigslist.
    mike



    --
    Wanted, Serial cable for Dell Axim X5 PDA.
    Return address is VALID but some sites block emails
    with links. Delete this sig when replying.
    FS 500MHz Tek DSOscilloscope TDS540 Make Offer
    Bunch of stuff For Sale and Wanted at the link below.
    MAKE THE OBVIOUS CHANGES TO THE LINK
    ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/
     
  7. mike

    mike Guest


    I can't argue with "faster is better", but it's easy to delude yourself
    into thinking a faster scope will make it easier to debug a digital
    thing. Analog scopes are great for periodic signals. Problem
    is that your digital thing is far from periodic. Unless you can
    trigger the scope on the parameter of interest, it don't matter how fast
    it is. And the problems hardest to solve are the most intermittent.
    I have a GAL20V8 on a breadboard with flying leads as a trigger
    recognizer. I write a custom program for the GAL to optimize the
    sequential event triggering to see what I'm looking for. Tedious, but
    powerful.

    The sweet spot of price/performance for analog scopes is 50-100MHz.
    Much faster and they've got too much custom stuff inside and can't be
    repaired by mere mortals. I'd vote for the TEK 465 family. 7704 mainframe
    scopes can be had dirt cheap, but get 'em with plugins. Ebay
    nickel-dime you into the poorhouse filling up the holes. Snag a full
    system with manuals and probes.

    mike



    --
    Wanted, Serial cable for Dell Axim X5 PDA.
    Return address is VALID but some sites block emails
    with links. Delete this sig when replying.
    FS 500MHz Tek DSOscilloscope TDS540 Make Offer
    Bunch of stuff For Sale and Wanted at the link below.
    MAKE THE OBVIOUS CHANGES TO THE LINK
    ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/
     
  8. Buddy Smith

    Buddy Smith Guest

    Here's a recent article about some of the PC-based oscilloscopes, which
    seem to be a pretty good value:

    http://www.ganssle.com/microscopes.pdf

    ttyl,

    --buddy
     
  9. GTR

    GTR Guest

    Although its been mentioned a number of times before, ebay is the way to go.
    Just make sure you buy from a seller with 99% or above and you will likely
    be fine. I bought my scope there and it cost me half of any other place I
    looked. As long as it is not *collectable* ebay is a great place to buy
    stuff cheap IMHO.
     
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