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Jon_G4MDC · 31st May 2020, 6:50 pm

Today the lash up board met the spectrum analyser. Actually the results were much better than expected and I was going to post some plots which I thought showed a minor victory. Spur levels were much better than measured before.

Then more messing around started to debunk those plots until I'm so confused I don't know what is right and wrong.

It all concerns the load presented to the output of the Si5351. If I connect direct to my spectrum analyser it is DC blocked by the capacitor in the input cable of 100nF. If I introduce a resistive 10dB pad directly at the Si5351 output (without DC block) the quite nice spur levels degrade considerably. I have yet to try DC block > 10dB Pad >SA. I hope that will produce consistent results with Si5351directly connected to SA without the pad.

It doesn't seem to be SA mixer related since SA input attenuation setting has no effect.
We program these for an output current strength so to DC block them or not?

31st May 2020, 6:50 pm	#35
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: LO for genuine 10m FM10D Pye Cambridge Today the lash up board met the spectrum analyser. Actually the results were much better than expected and I was going to post some plots which I thought showed a minor victory. Spur levels were much better than measured before. Then more messing around started to debunk those plots until I'm so confused I don't know what is right and wrong. It all concerns the load presented to the output of the Si5351. If I connect direct to my spectrum analyser it is DC blocked by the capacitor in the input cable of 100nF. If I introduce a resistive 10dB pad directly at the Si5351 output (without DC block) the quite nice spur levels degrade considerably. I have yet to try DC block > 10dB Pad >SA. I hope that will produce consistent results with Si5351directly connected to SA without the pad. It doesn't seem to be SA mixer related since SA input attenuation setting has no effect. We program these for an output current strength so to DC block them or not?