KF5OBS #32: Noise Figure Measurement (Gain Method)

One thought on “KF5OBS #32: Noise Figure Measurement (Gain Method)

  1. Thanks for the video. I enjoyed it 😉 Just some comments from a gray-beard…

    IIRC remember correctly, Y-factor gives you both the gain and noise figure of the DUT at the same time for the same amount of work.

    When I’ve measured noise factor (figure, or temperature) using a Y-factor, I would first check that my analyzer’s noise floor without the DUT is at least 20dB lower than with the DUT connected and cold terminated. If it is less, I must measure the difference and apply a correction factor. I did not see you do this and I am hard pressed to believe at least 20dB of measurement headroom exists with your MSO in FFT mode when you are already measuring at -101dBm at 10KHz RBW with the DUT connected. But I don’t have your instrument’s specifications in front of me now.

    I do not recommend leaving the input of the DUT unterminated. For various reasons (not the least of which is stability) the DUT should be terminated in its characteristic impedance and the thermal noise taken into account. If the thermal noise of the termination is too high for your DUT (satcom LNB?), then it is time to get out the Cold-Load and Dewar (that would be a fun video!).

    Always first examine your measurement traces at a higher RBW/VBW and/or a low averaging time to make sure something (DUT?) isn’t oscillating or throwing out spurs that will skew your final results. You may NOT see unwanted signals when aggressive RBW/VBW and/or averaging is applied.

    It is nice that your MSO displays directly in dBm/Hz. Properly calibrating the ideal noise equivalent BW of your instrument’s input filter and/or FFT binning is a pain in the neck.

    I’m not sure how this works with your MDO/MSO, but with a traditional spectrum analyzer, try to do your measurements with the reference level set such that your measurement is at the center of the display, not the top or bottom where calibration is typically not optimal.

    Best 73’s, David WB4ONA

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