Re: Does anybody know how to calibrate CEC firmware ?
The standard sources like the Tune Up page at http://www.hfsignals.com/index.php/ubitx-tuneup/ (for v4, v5 is a bit different with the calibration, with the uBitx transmitting what it thinks is 10MHz while you detect and read the frequency from an external device) and http://www.hamskey.com/2018/05/how-to-calibration-ubitx.html tell you the mechanics of doing the calibration, but I think they miss explaining the purpose.toggle quoted messageShow quoted text
“Calibration / Set to Zero Beat” attempts to adjust the Raduino clock frequency to match a standard by adjusting to a reference signal. The factory calibration likely gets you well within 10ppm, and that is close enough to work with—the frequencies indicated will be within 300Hz of the actuals, or 6 x 50Hz steps on the uBitx frequency dial. If you chase after 1ppm accuracy, you could end up be chasing local temperature variations or remote frequency variations that are smaller than the 50Hz/30MHz=1.6ppm step of the frequency dial.
The BFO (also called "Carrier" or “usbCarrier” in the source code) is more important because it is the final IF frequency and is what gets heterodyned into audio. V3&V4 boards use 12MHz (or 11995000Hz) and the V5 boards use about 11MHz (or 11053000Hz). Adjusting the BFO changes the IF heterodyning and with it the sideband window that gets filtered and decoded into audio, either including the carrier, warping the audio frequencies high or low, or pushing audio out of the filter bandwidth.
So, being mis-calibrated on the master calibration essentially makes your frequency reading on the dial off by a few steps or ppm, but being mis-calibrated in “BFO" interferes with the LSB/USB signal decoding and thereby the audio quality.