Ultimately I'm generating some spectrum plots in L-Band (1200-1800 MHz) and I need to get calibrated flux units (dBm/Hz) for my y-axis. I need a little assistance on creating this memo.
I've been tasked to use simply a 50 ohm matched load followed by the 2 LNAs and RTL-SDR v3 and use the difference between the front end ON vs front end OFF to arrive at a value I can use for my reference. I realize there are a few assumptions going on here (input impedance vs. gain, RTL tuner noise lower than thermal noise, etc.), but they can be ignored for this (unless of course the tuner noise is indeed higher than thermal noise).
I'm having trouble putting the equations together to arrive at what I ultimately want (the ratio of the two?). I know Sin = kT (assume B = 1 Hz?). So Sin = 4.045 x 10^-21 W/Hz or -173.9 dBm/Hz. I will use GQRX for observing the noise floor in dBf. Do I solve for Teq2 which I can use kTB to give me the total estimated noise floor?