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am I hooking up Oscope correctly

Discussion in 'Electronic Basics' started by john w, Dec 1, 2006.

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  1. john w

    john w Guest

    Hi,

    I just bought a mini-circuits zx60-8008 amplifier and am experimenting wth
    it a little.

    I need to find out if I am hooking it up to my Oscope correctly to measure
    what is coming out of it. Here is what I am currently doing.

    I hook the GND peg to the GND of my power-supply, then the +12 peg to the
    +12 of the power-supply.

    Then I input a signal into the IN coax jack of the amplifier.

    Then I have a short (maybe 2" long) coax cable attached to the OUT jack of
    the amplifier, with the insulation scraped off the end so I can attach an
    Oscope probe to it.

    Then I hook the + probe of my scope the bare center wire in the short coax
    attached to the OUT jack of the amp.

    And then I attach the GROUND clip of probe to the GND peg of the amplifier.

    Then I measure the signal coming out of the amplifier.

    So is this the correct setup to do measurements with an oscilloscope?

    Maybe I shoud be connecting the GROUND clip of the scope probe to the
    outside grounding sheath of the coax attached to the OUT jack of the amp
    instead? Does it matter, maybe this is actuall the same as attaching to the
    GND peg of the amp - like I am already doing.

    This is a basic question about measurement, but I could not find a diagram
    anywhere quickly that shows the correct way to do this.

    --thx, jw
     
  2. Phil Allison

    Phil Allison Guest

    "john w"

    ** The only such device I can find refernece to is the ZX66-8008E

    - a 20MHz to 8GHz lo-noise amp.

    That the one ??



    ** Not really.

    Forget the probe.

    You need to make up a lead with 50 ohm co-ax and terminate it with a BNC
    plug and a 50 ohm load at the scope end.

    Most wide band scopes have a switch setting on the front for 50 ohms input
    - this is the only way to avoid standing wave effects on the connecting
    cable.

    I hope your scope and generator have a more than 20MHz bandwidth or they are
    useless.



    ........ Phil
     
  3. ehsjr

    ehsjr Guest

    In general, you want the ground clip of the scope probe
    attached to ground as near to the signal you are probing
    as you can get it.

    Ed
     
  4. Is this an RF amplifier? If yes, is your scope up to the task? Generally,
    it is good idea to load RF amplifiers to 50 ohms or 72 ohms and keep the
    scope ground leads as short as possible. The coax ground is a better
    choice.
     
  5. redbelly

    redbelly Guest

    As others said, at these frequencies (> 20 MHz) you'll need a 50 ohm
    termination, if you're using 50 ohm coax.

    If you're scope doesn't have a 50 ohm setting on the input, you can get
    a convenient 50 ohm BNC in-line terminator from Thorlabs for 35 $US.
    It's part # T4119 here:

    http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=289&visual_id=2192&pn=T4119

    Mark
     
  6. john w

    john w Guest

    Thanks - I have got this going now. --jw
     
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