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FFT in LTSPICE XVII - force settings
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fcb:
Is there a way to force the setting of the FFT in LTspice (using XVII).

I'm already using the .four operative to create THD readouts successfully and also the FFT (View>FFT).

Problem is that it (FFT) doesn't seem to remember my 'specify a time range/time range' choices and requires resetting every simulation run (although it does remember my choice of window?).

?Any ideas if their are some operatives/instructions to force the the FFT?
SiliconWizard:
IIRC, the View/FFT computes an FFT over the portion of signal in the current window by default. I don't think there is any other way to make it "remember" the time range. So your best bet, if you want to issue an FFT over a specific time range, would be to define this time range in the transient simulation (time to start saving data/stop time).

fcb:
Thanks SiliconWizard.

That fix does work and is saving my sometime.  Still be nice if their were .op options to force the settings of the FFT, perhaps someone from LT/AD will read this.
Jay_Diddy_B:

--- Quote from: fcb on May 18, 2020, 09:37:02 am ---Is there a way to force the setting of the FFT in LTspice (using XVII).

I'm already using the .four operative to create THD readouts successfully and also the FFT (View>FFT).

Problem is that it (FFT) doesn't seem to remember my 'specify a time range/time range' choices and requires resetting every simulation run (although it does remember my choice of window?).

?Any ideas if their are some operatives/instructions to force the the FFT?

--- End quote ---

Can you share your model? or an example with the same challenges?

There may be a solution.

Regards,
Jay_Diddy_B
fcb:
Sorry Jay_Diddy_B.  It's under a fairly draconian NDA.

For anybody else searching how to do an FFT or THD (.four) using LTspice, this is the main resource I used:


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