IIP3 using transient analysis

Hi,

Can someone offer guidance on how to go about simulating IIP3 using transient analysis? I am aware that you can use PSS and PAC but I am having difficulty with convergence. The theory tells me that you input two sine waves and take the FFT at the output. But when I tried to input two frequencies (2.45G and 2.451G) using port it seems that only one sine wave is been produced. Any help on how to simulate IIP3 using transient analysis will be appreciated.

Thanks

Normally I put two voltage sources in series, one tuned to one frequency and the other tuned to the other frequency.

My question is how do I go about choosing the start and stop range when computing DFT since there are two different frequencies. What is the rule of thumb in choosing the appropriate range to cover the desired harmonics?

Thanks