I do a lot of analog work and have bene using the FFT function to help evaluate noise levels that selected OpAmps generate. The high frequency end above 10kHz is no problem but I need to go down from 1kHz to 10Hz. I cannot get the FFT function to go below 10kHz. If there is a way to do this with another Qspice feature please let me know.

Also, I really miss not having variable resistor and potentiometer to put on my diagrams.

Are you referring to waveform viewer FFT, or .four or .meas four ?

Minimum frequency in waveform viewer FFT depends on your simulation time.

FFT plot minimum frequency should be `= 1 / (Tstop - Tstart)`

For example, if you only simulate 1ms data, you can only expect FFT to give min freq at 1/1ms = 1kHz.

I ran a simple test and cannot observe problem in getting min frequency lower than 10Hz

I have created two potentiometer symbols, one assign resistance ratio in its instance parameter, one assign with external control voltage.

You can download these two variable resistors symbol (.qsym) from this link, file are Potentiometer-VCTRL.qsym and Potentiometer.qsym

Qspice/Symbols/analog at main · KSKelvin-Github/Qspice · GitHub

Parent.Potentiometer.qsch (3.8 KB)

OK - I was just changing the plot axis to move it lower. Now I understand what I need to do.

Thanks I will down load. This will help a lot.