When input is DC coupled, spectrum analyzer input amplifier does not tolerate any DC voltage. Yours say 0.2V in specifications, but it's really zero. You'd be foolish to risk applying any DC voltage to it. If you blow front end, it will cost you just as much as the whole SA to repair it.
Use A/C couple as much as you can. If you are new to this, you might even want to put on DC isolator on the input connector.
An only time you'd want to use DC coupling is when you want to measure very low frequency with limited amplitude, minimum of 30Hz and zero DC bias. Remember, really slow AC is same thing as DC. I've owned various specAn for few years now. So far, I never needed DC input. I actually have DC input (8568 has a separate input connector) zip tied, so BNC won't couple) disabled.
For such a low input frequency, FFT will be more suitable instruments.
Please be careful. Oooops will cost you plenty!