Re: Measurement problems, strange step noise floor behavior between 600-800kHz
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Have you set your o'scope for 50-ohms or using a 50-ohm feedthrough adaptor?
Dave - W?LEV
I just got a new TinySA Ultra (SeeSii store, Aliexpress) and get doubtful measurement results.
- I selected the cal output of 30MHz.
- connected the cal output with the SA input with an oscilloscope in between (50 ohm termination assumed to be provided by the input).
Problem 1: The scope shows about 40mV RMS which translates to -15dBm, but the TinySA shows the main peak at -35.5dBm on the fundamental 30MHz tone. Why is this?
Problem 2: The signal generator inside the TinySA claims to output -18dBm, but when measured with a scope on a 50 ohm load I measure around 285mV which corresponds to +2dBm. Why?
Problem 3: Using Nano VNA sine generator @140MHz with a 10dBm attenuator (because the NanoVNA outputs about +10dBm when set to 0dB!), measured with scope around 220mV RMS showing the tone in the TinySA of around -20dBm when it should show 0dBm. What is the problem here?
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I also did the linearity measurement which reveals no significant deviations (a straight line) across the attenuator steps at 120MHz and also at 200KHz and at 2GHz (at the latter frequency the peak showed up at -23dBm and "reduced linearity" warning showed up). All in all, seems no problem with the attenuator.
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Now to the strange noise floor behavior. Input was terminated and the noise floor started at 600KHz with around -85dBm and transitioned in weird steps towards -120dBm at around 1MHz. Does this indicate a problem?
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I do have historic background in RF engineering but I am relatively new to these new small devices and appreciate any feedback on what I identified as problems.
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Thank you in advance
Lutz
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