... | ... | @@ -10,7 +10,7 @@ As you can see, the second harmonics is only 55 dB below the first |
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harmonic level. The sine wave source was the Rhode & Schwartz SML01
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generator - expensive and solid looking device. To verify, if the input
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signal is free of the harmonics, we've connected another generator from
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the Agilent network analyser. Unfortunately, spectrum was looking the
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the Agilent network analyzer. Unfortunately, spectrum was looking the
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same, so the conclusion was to focus on the FmcAdc card. We did some
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additional measurements, for different frequencies, input voltage
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ranges, and signal amplitude, to find something that could help us in
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... | ... | @@ -18,10 +18,16 @@ the investigation. The observation that made us suspicious was the |
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harmonics level that did not differ due to the all changes shown above.
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Next step was to build filter that would suppress the harmonics, to make
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sure that input signal is truly clean.
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sure that input signal is truly clean.
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We don't care of the in-band nonflatness in frequency response, so it
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was decided to build Chebyshev filter,
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where edge sharpness is good.
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Schematic of the filter:
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Photo of the
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filter:
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filter:
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![](/uploads/40a1fe40de6a627f897a8d5ca9408fca/P1040722.JPG)
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Frequency response - marker at the frequency that is subharmonic of the
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