looking for some help with finding the transfer function of a vco circuit. hopefully my explanations here are clear enough

on this (http://www.minicircuits.com/app/VCO15-10.pdf) and other websites, that the transfer function can be given by Ko/s, where Ko is the slope of the oscillator frequency over the voltage (with units rad/(s * V))

So what i have done so far is, by simulation of a VCO circuit, enter a control voltage and measured the corresponding oscillator frequency. I then multiplied the oscillator frequency by 2*pi to get the value of ω (rad/s).

I then plotted the control voltage vs ω to get the value of Ko. If it matters, the relationship between the frequency and the control voltage was found to be linear, which was something i expected. So with this plot, i found the slope (ω1-ω2)/(V1-V2) in order to find the value of Ko.

In order to check my work, and to verify that this transfer function is correct, i built a simulation in Simulink that accepts the control voltage as the input, multiplies it by the value of Ko that i found, integrates, and then spits out the output.

What I expected the output to be is the oscillator frequency for that particular control voltage. However, this did not seem to be giving the correct solution. Does anybody have some insight on where I might have gone wrong?

Thank you.