Hello Fernando,
Yes, the peak at 1Hz is 0Hz and expected.
If you are no longer seeing your input signal in the SA44B, then we need to consider the possibility of a damaged attenuator/RF front end, often the result of a high input DC or static. Please email your details to justin@signalhound.com and we can begin the RMA process if indeed this is the determined outcome. We look forward to your email.
Regards,
A.J.