Could be that different rigs exhibiting obnoxious audio tones
are due either or both oscillators.??
Luck of the draw as to where those ceramic resonators land.
Could tell which one by varying the BFO, if 100hz shift in the BFO
causes a 100hz? shift in the audio tone, then it's the 12mhz osc.
If a 100hz shift in the BFO causes a 400hz shift in the audio tone,
then it's the 16mhz osc (since 12mhz*4 = 16mhz*3 = 48mhz).
A 9600 baud rate can be generated from any osc above 1mhz
by using the appropriate divide factor.
The CH340 takes 5v in, the internal 3.3v regulator supplies the si5351.
And it's on the backside of the Nano.
Good luck hacking that.
Jerry
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On Mon, Apr 9, 2018 at 11:03 pm, John Backo wrote:
The baud rate is the effective data rate. It still has to have some kind
of frequency driving it. Perhaps the most effective solution is to switch
the supply voltage to the CH340 chip. That is 3.3v at pin 19, I believe.
The chip is tolerant of 5v from the USB connection, but ordinarily operates
at 3.3v. There is no serial converter chip (as shown in the "normal" configuration
in the datasheet. The TXD and RXD lines connect directly to the ATMega chip.
It would be a delicate operation to switch and thus disable the power input line, but
it could be done.
Has anyone investigated that the USB connection might be a source? It has an internal
frequency control in the computer. But it is an unlikely source, especially when disconnected.
john
AD5YE
