Noise measurement with Femto Preamplifier

Hi,

I trying to do some noise measurements with the SA44B.
Measurement setup:
Photodiode (with BIAS) connected to an preamplifier (Femto DLPCA-200, AC filter, 500kHz Cut off frequency, gain 1E3 V/A, 50Ohm). The Femto converts the current to an amplified voltage. Output of the Femto connected to SA44B.

Setting Spike Software:
Trace: Type: Average
Acquisition: Video Units: Power
Detector: Average
Bandwith: RBW Shape: Flat Top
RBW:10Hz
VBW:10Hz
REF Level: -50dBm
Start: 1Hz
Stop 200kHz
Spur Reject: Off
Gain/Atten: Auto

1. Question: When I substract the gain of the Femto. For example: I measure -120dBm. The real value of the photodiode would be -150dBm. (Gain 1E3 equivalent to 30dB)
Or have I to transform the measurement first in V/sqrt(Hz) and then transform it to A/sqrt(Hz) by deviding with 1E3

I did it like here:
https://signalhound.com/support/forums/topic/unit-conversion-equations-dbmhz/
First from dBm to dBm/Hz than dBm to dBW and than to Voltage.

2. Question:
A spectrum analyzer using log power averaging displays a random noise signal 2.5 dB below its actual value. For more information refer to Keysight Application Note 150, Spectrum Analysis Basis, August 2006, 5952-0292.
http://literature.cdn.keysight.com/litweb/pdf/5989-5742EN.pdf

Does this have to applied to the measurements made with the SA44B?

Thanks for helping

Flo