I have begun to do the test on the system, I have just get an spectrum analyzer and a amplifier. Unfortunately I don't have a noise source, but I have tried to measure de noise generated by a 50ohms terminator placed in the input of the amplifier. The noise figure of this device in unknow, I have estimated the gain by measuring different synusoidal frequencies and it is about 140 with a bandwith of 1GHz. The preamplifer of the spectrum analyzer has a NF of 11dB.
The problem is that I am obtaining less espectral density than the expected in input (about 805pV/sqrt Hz, while 50ohms have to have about 900pV/sqrt Hz). I have check that the gain compression begins at 1mVrms in the input, so I am far away from compression region which could explain such a low espectral density value. I also check the amplifier with a vector network analyzer and it has a reflection in the input of about -0.2 at 700MHz, could this be related with the obtained reduced noise values? suggestions or ideas