I'm doing an RF test where the output of a 2.4GHz 2W PA is connected to a SA through a few attenuators. The signal is QPSK modulated data.
When I put 3x 30dB attenuators in series, I get the expected power measurement of -57dBm (33-90) at the SA. But when I put a 4th attenuator of 20dB, I still get the same power level of -57dB at the SA rather than -77dBm. The noise floor of the SA is -93dBm with the selected RBW. What could be the reason for this strange observation? Some kind of leakage?
When I put 3x 30dB attenuators in series, I get the expected power measurement of -57dBm (33-90) at the SA. But when I put a 4th attenuator of 20dB, I still get the same power level of -57dB at the SA rather than -77dBm. The noise floor of the SA is -93dBm with the selected RBW. What could be the reason for this strange observation? Some kind of leakage?