Re: #ubitx-help Strong Audio Tones in and outside audio receive passband #ubitx-help

Jerry Gaffke
 

Bingo!
See this ceramic resonator on Mouser:  pnum  81-CSTCE16M0VH3L99R0
Same physical size as what's on the Nano, I didn't see any quartz crystals that small.
Tolerance of those Murata parts is 0.07%, so could be off by as much as plus or minus 16mhz*0.0007=11.2khz 
Whatever they stuff on a $2 Nano is probably not Murata, unless they are Murata rejects.

This internal oscillator capacitance thing, is though only in the interest of accuracy?
Or is it a matter of the oscillator not working at all?

Regardless, anybody with tones, I suggest you pack some capacitance across pins 7 and 8 
of the ATMega328P chip (hard to get at those signals on the very small ceramic resonator).
I have no idea how much, perhaps hundreds of pF, if the Raduino display no longer works then that's too much.
This might be something best done at hfsignals on new units, as those 328P pins are pretty small

And if that doesn't help, try shorting out one end of the 12mhz resonator to ground.
Found on the back of the Nano, unfortunately.



On Sun, Feb 4, 2018 at 09:15 am, Arv Evans wrote:
Not 100% sure but popular thinking indicates the "crystals" on smaller Arduino boards are actually ceramic resonators.  If this is true then it should be possible to use capacitence to pull them further than would be possible with a real crystal.  This also lends credibility to the caution about possibile need to change AVR internal oscilator capacitence if changing resonator or crystal device.
 

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