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Data along the path to resolution...

No cigars or celebrations just yet! But some data points to ponder. One input from a blog reader was that the LO quadrature signals were not quadrature, or 90 degrees out of phase. 

Using the XY function on my Siglent scope if you have two sine waves exactly 90 degrees out of phase the resulting plot is a perfect circle. But the output from a Si5351 is more like a square wave and two square waves 90 degrees out of phase produce a tilted square.


This is the XY Plot of CLK0 vs CLK2.


The Tilted Square is indicative of a 90 Degree shift between CLK0 and CLK2. So, check that off the list.

Another reader input was that the quadrature signals coming from the Sound Card on transmit was an issue. Below is a photo of the I and Q outputs from the Sound Card on transmit. There is slight difference in amplitude which I think can be corrected in the Pulse Sound App. But what I see is about a 90-degree shift and very good-looking waveforms.


Amplitudes are Different but Correctable


Pulse Audio Panel Adjustment ~ Closer


Sine Wave Phase Shift: Not a Perfect Circle!

We now have some interesting data for further analysis in that we can see a sine wave output on transmit for the I and Q channels and we have the ability to balance those output levels using the Pulse Audio Control Panel. I also believe using the QUISK embedded tools we can make the I and Q a perfect circle on transmit.

What we are doing is an issue elimination process on the road to problem resolution. Not close, but sure a learning process.

Them that know can make things go. 

73's
Pete N6QW

 

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