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For example, how would I see the ratio between Vi and Vo for a linear AC simulation?

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  • \$\begingroup\$ An .AC simulation means the circuits are first linearized, so there is no nonlinear .AC simulation. \$\endgroup\$ – a concerned citizen Mar 4 at 8:15
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As you can read here, LTSpice can plot a mathematical function of the traced variables. You just have to edit the plot to specify the functions.

An example from the from the linked page is shown below. As mentioned in the comments, to edit the plot function you can right click on the name. The plot name is the green string starting with "1.1*pow...".

enter image description here

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  • \$\begingroup\$ Great! Stupid question, how do I get to the expression editor? (I'm on a Windows machine.) \$\endgroup\$ – J.D. Mar 3 at 20:25
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    \$\begingroup\$ Right click on the trace name. The green (1.1*pow(V(9) ...) in picture above. \$\endgroup\$ – Huisman Mar 3 at 20:56
  • \$\begingroup\$ Thank you! I'm a first time user for LTSpice. Your help is much appreciated. \$\endgroup\$ – J.D. Mar 3 at 23:06
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What you see in an AC simulation is the ratio, but expressed in decibels. To see the ratio properly you would need to change the Y axis from logarithmic to linear. (right click)

enter image description here

This will be expressed in volts still but you can change the expression from V(y) to V(x)/V(y) as in crj11's answer.

enter image description here

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