I have a tracking station for UHF band satellites which comprises of a cross yagi of 12 dBi and a wideband LNA of 40 dB Power Gain and 1.3 dB Noise Figure. I observe a Noise floor of about 300 kHz centered at the frequency of 436 MHz on the spectrum analyzer. The floor power varies between -75 and -80 dBm, while the floor at other frequencies is -100 dBm.
I tried reducing the RBW and VBW of the analyzer, but the floor doesn't change. I tested both antenna and LNA separately and couldn't find the reason for this floor. Please help me.