Eduk,
We have observed, when the preamp is used, at 0 dB of attenuation, it can take a long time for the DC blocking cap to reach steady state (up to 30 seconds). Typically, setting your reference level to -30 dBm briefly (preamp on, attenuator 5-10 dB), before proceeding to maximum sensitivity, allows quick settling.
On a fraction of units, the preamp’s DC blocking cap never reaches steady state without a better DC path to ground. We typically have to add a 2.2k resistor to help bleed this off. You can contact us for a warranty repair if your SA44B is exhibiting this behavior. I apologize for the inconvenience.
We will be updating the design to add this resistor in the near future.