Calibrating an Si5351 VFO with Arduino Software

[@richonguzman]

great! im just about to follow you as I'm also learning to build my own qrp radio CA2RXU, 73!

[@mixradiointernationalshortwave]

Other DSS VFO sketches have a frequency calibration mode menu feature. Maybe one can be added as it will be a lot easier than having to load it from a computer every time.

[@Q26Video]

Thanks - yes, that would be possible and I will probably include it when I make a more permanent version of my radio...

[@mixradiointernationalshortwave]

@@Q26Video If you could make the sketch available so I can add it to mine that would be great. Thanks.

[@Q26Video]

When I've done some more on this I will make it all available - it may take a while... 🤓😃

[@devilvortex1]

is that a Tiny UPDI-HV Programmer ?

[@Real_Tim_S]

Would it not make sense to calibrate at a much higher frequency? I would think higher frequencies (like 4x your maximum expected operating frequency), the total error at lower frequencuiies would be almost a non-issue. Also, are you using a TCXO on the Si5351?

[@Q26Video]

Hi Tim - I'm following the guidance of NT7S (Jason) and his etherkit library for Arduino and Si5351 - his calibration sketch shows an example of 10MHz and that worked really well for me. I also tried at some other frequencies, eg in the 14MHz band. Getting an accurate zero beat to work another station is really important for QRP and the point of this video is to show it can be done even without specialist equipment (and I did improve on it off camera 🤓😃). 73 from Mort / G4BSK

[@Q26Video]

...and no TXO - just a plain vanilla crystal...

[@Real_Tim_S]

@@Q26Video Thanks for indulging me. One other question I was not able to answer from a slightly more than cursory read of the datasheet - what is the VFO adjustment range of the analog input, and do you have any experience with the transient response of that SI5351 part? I am curious if that would be suitable for an OFDM transmitter (by directly modulating the VFO input with an external DSP, like say an ESP32).

[@Q26Video]

Sorry Tim, I have no experience or detailed knowledge about any of that - sounds like an interesting project and I hope you figure it out. Best wishes, Mortimer

[@carlo_geiss]

wow thank you Mort ... i never think about this difference ... it's very helpful ... 73 SA2KHG/DG5FW de Carlo