As recommended by Manuel, I've been using my nanoVNA to tweak the Lx2 inductors to tune the 2nd harmonic 'trap'. The RF boards I purchased for our group's 'boards only' buy did not have 1nF capacitors available when i ordered the boards, so I bought some GRM2195C2A102JA01D capacitors.
When I was adjusting the 7 MHz filter with the nanoVNA, I noticed that the filter didn't 'roll off' on the 3rd harmonic like it did on my 2nd RF board.
On closer inspection, it looked like C35 wasn't soldered correctly. After I touched up the capacitor, here's what the filter output should look like: (Apologies as the scale used isn't quite the same)
This will probably provide better suppression of the 3rd harmonic on 21 MHz
Edit; As an added bonus, the power output went from .61W to .89W when powered with 5Vdc via the USB port. Efficiency is still 88%
Using nanoVNA to find cold solder joints in the RF board
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Using nanoVNA to find cold solder joints in the RF board
Last edited by va3rr on 21 Mar 2022, 18:53, edited 1 time in total.
Slava Ukraini!
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Re: Using nanoVNA to find cold solder joints in the RF board
Good finding ! Thanks for sharing with us !
73 Manuel; DL2MAN
73 Manuel; DL2MAN
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