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still a newbie - another getting started with LT SPICE problem

Discussion in 'Electronic Basics' started by dave, Sep 5, 2007.

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  1. dave

    dave Guest

    Still having a problem understanding this aspect of LT Spice.

    Say I draft a circuit. I must put a (voltage) source in - say sine at
    a constant frequency

    eg SINE 0 10 150.

    If I then want to see what happens to that circuit across a range of
    frequencies I must insert a .ac command, which allows me to specify a
    start and stop frequency.

    eg: .ac lin 50 100 1000

    when I do this I get an error saying

    No AC stimulus found:
    Set the value of a current or voltage source to "AC 1."
    to make it behave as a signal generator for AC analysis.


    I'm clearly not understanding dot commands (and probably lots of other
    things) - but I thought I *had* set an AC stimulus with the SINE
    "generator device" (A circle with a + - in it and the word SINE and
    <args> along side it. I also thought (perhaps) the frequency arg in
    the sine command would be replaced by the frequence sweep in the .ac
    command - but it seems it completlely separate.

    Please… explain what I should do to do this correctly.
    Thanks
     
  2. Andrew Holme

    Andrew Holme Guest

    In the properties dialog of the voltage source, you had the SINE function
    radio button selected. Change this to NONE. The small signal AC analysis
    fields on the right-hand side will then be enabled. Enter 1 in the AC
    amplitude field and click OK.
     
  3. dave

    dave Guest

    Ah I see. Thanks.
     
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