USB-SA44B use as an audio spectrum analyzer

The SA44B has sufficient real time bandwidth (250kHz) and certainly covers the audio frequency range (1Hz to 4.4GHz).
The low end detection of -151dBm is more than capable of picking up low level signals.

The only issues I see are:
– you must block any and all DC
– its an RF device so its input impedance is 50ohms. Not 1Meg//28pF like the HP unit.
– you should probably put an in-line attenuator to make sure the input doesnt exceed +10dBm (into 50R)

So the answer is yes, in theory. In practice it may be more involved…

Hope this helps,
Regards,
Jared