How to increase the frequency resolution in FFT?

I’m still learning. I have checked many questions on here similar to mine, but have not found an answer.

I’m analyzing the oscillation of a train catenary system. Due to bad sampling frequency and short time periods of interest, I don’t have that many samples. Additionally, four recorded frequencies are apparently around 0.92 Hz. I can’t tell them apart in the frequency spectrum and thus want to increase frequency resolution. I think I will not be able to distinguish them all, they’re too close, but maybe at least two or three.

This is my signal in time domain:
catenary displacement over time

I know I need to increase the number of samples I feed into the FFT. I have read that zero-padding might be an option, but have also read that it leaves artifacts and is not suited to increase frequency resolution. I have also read that the signal can be mirrored along both axes and added in the end, which I don’t think is a good idea for this signal. I thought increasing samples by adding interpolated samples would be an idea, since it also wouldn’t be that time-consuming considering the low amount of samples.

Are there options I missed? Does my idea sound dumb?

Read more here: Source link