How to use pwelch correctly for signal processing

Hi,

I would appreciate if someone can guide me the right approach to use pwelch of the signal I have.

My signal is sampled at 3051Hz.

It has base frequency at ~1.5Hz.

And also another fequency around tens of Hertz (not sure exactly).

I use the pwelch with it's default values but I cannot see the 1.5Hz very good.

Do I need to use other values than the default? What should they be?

I'm attaching my signal.

My final goal is to design a high pass filter that would reveal these frequencies.

Thanks in advance! Omri