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Wednesday, June 30, 2021

10 Pole Crystal Filter Passband as Seen in Antuino and NanoVNA

I continue to work on the "Mythbuster" rig,  but I am taking it slow, trying to learn something from each stage.  I'm especially trying to master the used of the great test gear that has arrived in my shack in recent years:  The Antuino, the NanoVNA, and the TinySA.  

Above you can see the passband of the 10 pole crystal filter as measured across the 50 ohm terminations on the filter.  I use simple FT37-43 transformers to match the filter impedance down to 50 ohms.  I used the Antuino first -- it scanned the passband and held the image on its screen.  I then disconnected the Antuino and connected the NanoVNA.  So in this shot you can see the passband on both devices.  

You will notice that the Antuino says there is a 20db insertion loss.  That's only because in the Antuino 20db is really 0 db loss.  I think the NanoVNA gives a more accurate insertion loss reading -- about 3-5 db.  The cool thing is how similar the shapes of the passband are.  

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