I need verification that I am computing the noise factor (NF) of my emissions receiver correctly. The system will measure emissions in the 1-10 GHz band and will use a horn antenna followed by a high pass filter followed by a preamp feeding a spectrum analyzer. I can ignore the NF of the spectrum analyzer. since gain of the preamp is 20 dB, so the total NF will be set by the other three elements. The NF of the preamp is 4 dB, the insertion loss of the filter is 1 dB and the antenna factor of the horn is 39 dB at 10 GHz. I understand that the NF of the filter will be equal to the insertion loss, 1 dB. And the NF of the antenna will be equal to its insertion loss (antenna factor), 39 dB at 10 GHz. Therefore the total NF of the three elements will be the sum of their NFs - i.e., 39 + 1 + 4 = 44 dB. It seems that I don't have to be overly concerned about the NF when I select a preamp, since the only way of reducing the NF significantly would be to improve the antenna factor. Are my calculations correct?
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