jmatusiakParticipantjmatusiak January 10, 2022 at 8:46 am
Using Spike, if I look at the spectrum of the first 1GHz with an SM200C, I see quite a bit of noise. I don’t believe that this should be the case, so I am hoping that maybe there is some sort of calibration I need to do to clean this up (the spectrum looks a lot better above 1GHz.
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Justin CrooksModeratorJustin Crooks January 10, 2022 at 10:28 am
I’m not sure what signal you’re looking at there, but it is possible that level of noise is actually on your signal. You can turn the preselector on and off below 640 MHz, and change your reference level by 10 dB. If the noise level changes considerably, it may be partially from intermodulation inside the SM200C. Otherwise, it is likely part of your input signal.
jmatusiakParticipantjmatusiak January 11, 2022 at 7:08 am
Thank you for the sanity check. Tossing a 50ohm load on the antenna port shows a spectrum like one would expect (the lower band is much quieter and is just some noise like the rest of the spectrum).
I do want to investigate the pre-selector option you mention though, as I can still see an increased noise floor from DC to ~640MHz (maybe ~5dB).
Justin CrooksModeratorJustin Crooks January 11, 2022 at 9:54 am
You will notice in the specifications that the DANL (noise floor) specification is 4 dB higher below 700 MHz vs. above 700 MHz. A 4-5 dB step in the noise floor is normal. This is due to a design decision to optimize for noise figure in the 700 MHz – 2700 MHz communications band, and to push for better linearity at low frequencies.
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