Hello Maurool,
The IF bandwidth of the SA44B is only 250kHz (internal sample rate of 486kS/s). This is the maximum bandwidth on which you can make instantaneous measurements. A 2 or 4 MS/s sample rate would produce a signal with roughly 2-8MHz of bandwidth, exceeding the BW of the SA44B.
The BB60C is our most affordable analyzer that could measure signals with these sample rates with a IF BW of 27MHz.
Let me know if you have further questions.
Regards,
Andrew