as3935
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| as3935 [2024/04/12 04:57] – river | as3935 [2024/07/25 22:33] (current) – [Calibration] river | ||
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| A badly designed, pulled, aged, uncompensated crystal oscillator might be 50ppm off, so much better than needed as a calibration standard for this application. Therefore can use a µC to calibrate it automatically. I don't see this done in the Sparkfun library even though it seems obvious. | A badly designed, pulled, aged, uncompensated crystal oscillator might be 50ppm off, so much better than needed as a calibration standard for this application. Therefore can use a µC to calibrate it automatically. I don't see this done in the Sparkfun library even though it seems obvious. | ||
| - | The chip can the calibrate its clocks from the above value, so antenna should be trimmed first. | + | The chip can then calibrate its clocks from the above value, so antenna should be trimmed first. |
| Clocks calibration must be repeated after power loss. | Clocks calibration must be repeated after power loss. | ||
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| Over the next hours I noticed the capacitance drifted back down again, needing more from the trimcaps. Maybe board drying out or cooling down? The next day it was using 96pF or 88pF trimcaps. | Over the next hours I noticed the capacitance drifted back down again, needing more from the trimcaps. Maybe board drying out or cooling down? The next day it was using 96pF or 88pF trimcaps. | ||
| + | |||
| + | Next day, added 51pF. Now it gets: Trimcap: 0pF, Error: -134 Hz, -0.0% | ||
| + | |||
| + | Also added 22uF ceramic to power socket pins, and 1nF from IRQ to ground. Removed electrolytic. Also modified µC board - added bigger 3.3V regulator with ceramic caps and 470uF input cap. | ||
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| + | Get occasional QRM reports but nothing like without any caps that started with. | ||
| ===== Noise ===== | ===== Noise ===== | ||
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| (Not extensively tested, maybe reading other registers works too.) | (Not extensively tested, maybe reading other registers works too.) | ||
| - | I read than some boards have wrong tuning caps. I couldn' | + | I read that some boards have wrong tuning caps. I couldn' |
| ===== Links ===== | ===== Links ===== | ||
as3935.1712897831.txt.gz · Last modified: by river