Network Analyzer Anomaly

[Shalom]

I'm playing with the Network Analysis capability on the Analog Discovery 2 and see something curious and I was hoping you could explain it to me.  See the attached image, from WaveFroms, as a reference for my question:

I'm getting the Bode plot of a System/Filter.  You'll notice that Channel 1 (yellow) is the input to the system and Channel 2 (blue) is the output.  The plot shows the Magnitude of each channel relative to Channel 1.  What bothers me is that Channel 1 should always be 1 to 1 (or 0 dB) with respect to itself.  You'll notice that this seems to be the case up to about 10 kHz when all of a sudden Channel 1 becomes about -3 dB less than Channel 1 (itself)... that's odd, I would imagine that I should see the yellow line be strainght across at 0 dB the whole time.

it does indeed show that the yellow line should be straight across in your documentation see here: https://reference.digilentinc.com/learn/instrumentation/tutorials/ad2-network-analyzer/start

So I'm just confused at what is going with my plot.

Thanks! Shalom

[attila]

Hi @Shalom

This is expected.
The Wavegen output (Scope channel 1) is attenuated because your circuit impedance lowers above 10kHz.
The Wavegen can drive min 10mA max 50mA depending on voltage. Due to this the generated signal will be clipped. 
When using the BNC adapter with 50 Ohm termination the signal will be attenuated proportional to the load.
The Scope channel 2 represents the circuit characteristics since the 'Relative to Channel 1' is checked.