How good, or bad, is the tinySA?
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When trying to measure the spurs of a SI5351 the first measurement caused some doubt on the performance of the tinySA.
Is the output of the SI5351 really that bad? The output of the SI5351 is connected to the input of the tinySA using a 20dB attenuator Output frequency of the SI535 is set to 135MHz. A signal 346.6 MHz appeared and this should not be there because the LO low pass filter is still present and it has no direct harmonic relation to 135MHz Then I remembered my own advice. Always use a 10dB attenuator to test if the harmonics you see are really part of the input. This led to a much improved measurement, all harmonics above 150MHz are now suppressed. The spurs around 135MHz are caused by the fractional divider in the SI5351 but what is causing the 76.6MHz and 211.6MHz signals? Time to switch on the spur reduction. And that made a big difference. The?76.6MHz and 211.6MHz signals are (almost) gone and this measurement is very much like when using a much better SA. So keep in mind when you build and use the tinySA: it is easy to get wrong measurement results! -- HBTE Files section:?/g/HBTE/files Erik, PD0EK |