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What Oscilloscope to get

Discussion in 'Electronic Equipment' started by Ben Wheare, Sep 18, 2006.

  1. Ben Wheare

    Ben Wheare Guest

    Am looking for one that can do the following:

    Analyse RS232 comms, logic gates etc
    Freeze trace would be nice (storage scope), but probably pushes the
    price up.

    Don't need anything ultra-amazing, am currently looking at
    http://www.stewart-of-reading.co.uk/sor_oscilloscopes.html - the
    Tektronix 465B for £75 looks good or maybe the HPS5 Velleman. There is a
    Farnell DMS3580A storage scope listed, but google returns no results for it.


    Any advice which one would be decent?

    Thanks,

    Ben
     
  2. Ben Wheare

    Ben Wheare Guest


    I'd also consider a PC based oscilloscope - this might be a better
    solution, any recommendations?
     
  3. Jean-Yves

    Jean-Yves Guest

    to analyze correctly rs232 frames I would suggest this :

    http://www.pctestinstruments.com/index.htm

    but it's rather around £250 than £75...
    but to analyze a rs232 comm with a tek 475 you will have some time to
    loose...
     
  4. Rich Webb

    Rich Webb Guest

    Another vote for the LogicPort from the link above. Wonderful little
    device, portable, and has a built-in interpreter for serial data, with
    user configuration options for data bits, stop bits, parity, and
    polarity. The demo that runs without the device installed is the
    production release and gives a good idea of its capabilities.

    For low priced scopes with storage, look at the Tek TDS1000/2000 series.
     

  5. Or maybe two scopes: the pc based for low-repetition and digital
    storage if needed, and the £75 Tektronix 465 if analog performance is
    necessary.

    Choice depends on the needs and the budget one has ;-)

    hth,
    Andreas
     
  6. colin

    colin Guest

    it.

    I got my first scope from them many years ago, a tek585a
    made a good room warmer too ! and several other bits.

    I use a hp1740a now, (with a home made 4ghz sampling unit).
    I find I could do with more traces/bandwidth+storage sometimes.

    depends what you want to analyse with the rs232 stuff,
    if you just want to look at bit levels etc
    or if you can bang out the same bit/byte pattern repeatedly,
    most scopes would do,
    but if you want to analyse byte streams youl need far more than a scope.

    Colin =^.^=
     
  7. colin wrote:

    Tell us more!

    Andrew
     
  8. colin

    colin Guest

    Sure,
    Its quite basic, I started with this circuit but wasnt happy with it ...
    http://www.elecdesign.com/Files/29/4749/Figure_01.gif
    although I never bothered with the delay line, and I used a DG RF mosfet for
    the high speed ramp.
    I also provided a slow speed ramp generator instead of using the scope trace
    output, and I used single 5v supply instaed of +-2.5v with ac coupled ip.

    so I modified it, now an ECL D type flip flop with set/reset provides the
    trigger wich trigers upto 2ghz or more
    this holds itself in reset for 50ns then locks itself out for a further
    50ns,
    (it didnt like this at first with metastable states so an LC was used to
    delay the feedback)
    so with say a 2ghz input you get a 10mhz sampling rate,
    this drives a high speed ramp wich is just an emitter follower and constant
    current source down to ground,
    this is tricky to get right as small ripples at the start cuase timebase
    distortion
    this is compared with a slow speed ramp by an ultra fast comparator,
    this locks itself out so it generates a squarewave delayed from the sampling
    rate signal,
    the differential op from the comparator drives a 4ghz sampling unit I got
    from ebay wich is just an SRD and 2 schotky diodes and 2 capacitors, this is
    much better than the diode switches but it is incredibly delicate
    an antiparallel schotky diode clamp is accross its input,
    this just drives a fast cmos op amp with a gain of 10,
    input attenuation is used to provide a maximum op of 2vp-p. and aprox 1:1
    gain.

    the timebase is variable but I have it at 500ps/div on my scope atm,
    the slow ramp generator is set to 2ms rate, its possible to see artifacts
    wich are 4ghz.
    the amplitude agrees with a schotky detector upto 2ghz wich is as high as I
    have used it so far.

    Its made on 2side pcb made by guage isolated tracks.
    It still gets modified quite often still as I think of ways of improving it,
    so I havnt got a definitive circuit.
    I could do with a way of checking the acuracy of the trace.
    also its hard to probe around at 2ghz+, I generaly put smc coax sockets on
    the pcb at various points,
    and 500R from there to the point of interest.

    I keep meaning to remake it with a few bells and whistles etc...
    the old circuit is also along side it with the same comparator driving the
    diode switches and the sampling unit.
    The SRD takes about 50ns to turn off so it is delayed considerably compared
    to the diode switch chanel.
    im also adding a prescaler on the trigger ip for my freq counter.

    Atm im using it to debug a heterodyne lidar wich uses modulated laser light
    at 1ghz+ hopefully upto 2ghz.

    Colin =^.^=
     
  9. colin

    colin Guest

    oh and the slow ramp generator inserts a neg sync pulse into the op so its
    easy to trigger.

    Colin =^.^=
     
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