All three local oscillators into the uBitx that determine the operating frequency
are sourced by the si5351.
And the clocks out of the si5351 are strict ratios of the 25mhz reference frequency
So any error in the 25mhz reference clock will be exactly proportional to the error in your displayed operating frequency.
Assuming the firmware was done correctly.
Example:
When tuning to the rig to 14.0mhz, you find that you are receiving a signal at 14.001 mhz.
Then the 25mhz reference must be at 25.0*14.001/14 = 25.001786 mhz?
That's a 1e6 * 200hz/14000000hz = 14.3 ppm difference.? ?(where 1e6=1,000,000, to convert a ratio to parts-per-million)
Makes me wonder how much of a temperature change is involved here.
Mark had previously reported a roughly 1ppm drift in his Adafruit si5351 board.?
Jerry
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On Sat, Nov 3, 2018 at 04:33 PM, K5ESS wrote:
FWIW when I operate 20 meter FT8 with my uBitx the WSJT-X waterfall display clearly shows about a 200 Hz upward drift for the first 10 to 12 minutes after I power it on. I don't know how that would translate to the drift in the 25 MHz crystal reference.
Mike
K5ESS
