Right now you have 20dB of attenuation. I recommend 30dB of attenuation and an RF limiter.
The RF limiter will protect the front end of the SA, the 30dB of attenuation is necessary to bring your 40dBm signal down to 10dBm where the SA is no longer in compression and can accurately measure the input. Our RF performance specifications only hold to +10.
Regards,
