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

Jerry Gaffke

Not familiar with the ATMega328P, but table 9.3 on p300 of the datasheet says the Low Power Crystal Oscillator
can take a crystal anywhere from 0.4mhz to 16mhz, and that we must load bits CLKSEL[3-1] to inform
the chip what the crystal frequency is.  The top range with CLKSEL=111 is for 8 to 16mhz, so I assume
we could have a crystal anywhere in there without having to burn fuse bits.
My datasheet has the unfortunate name of:  

The primary reason not to swap out the 16mhz crystal is that the one they have is so blasted small.
Take a look, it's visible on your Raduino's Nano, just above the Nano pin labeled "D5".
Not all of us would want to deal with it.

If we disable or remove the USB-to-UART chip from the Nano (and make sure we have some sort of 3.3v regulator),
we can still program the Nano via the TX/RX Uart lines at D0,D1 of the Nano board edge using an external
FTDI USB-to-UART cable or similar.  Unfortunately this probably means separating the Nano from the Raduino
to work on the bottom of the Nano, so probably not an option.  Thus far, it seems the 12mhz USB crystal
is not an issue though, since reports of tones come with the news that the tones change when
a finger is placed on the 16mhz crystal.  Could be the 12mhz crystal is involved here too though.

Jerry, KE7ER

On Sat, Feb 3, 2018 at 10:15 pm, James Lawrie wrote:
I know I'm late to this party but you cannot swap crystals on nano board without first using a atmel programmer to burn the fuse bits that tell what freq it will be using or you will brick your nano.... also if the ftdi or whatever usb chip is using 12mhz, you could get the sparkfunPro 16mhz/8mhz board that does not use usb but instead uses usb to serial cable to upload. Be warned 16mhz board is 5 volt and 8 mhz is 3.3 volt.

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