Read The Manual

 I started to fool around with the Si5351 on the Nano.  First I tried to generate the 112.5 MHz signal on ch0 with less multiplying and less dividing but I got this:

exactly 1/2 the desired frequency

Apparently the oscillator frequency MUST be in the range of 600 to 900 MHz to use the integer mode ?  The sine looking wave is again probably the result of the 100 MHz bandwidth of the scope stepping on the harmonics - it is always weird to me that the fundamental frequency of a square wave is LARGER than the peak to peak voltage of the square wave.  In this case the sine fundamental is almost 5 volts while the square wave peak to peak should be 3.3 volts (the supply voltage).

Then I tried to set the ch1 frequency to 5 MHz and that did work, eventually:

I used the fractional mode but neglected to put a 1 in the denominator of the fractional part even though the numerator is zero in this case.  So the output was a flat line.

It is time to read the manual !

I also downloaded the Clockbuilder app from Skyworks who now own the Si5351 design.  I was thinking I could use that to do a simple .asm program for a PIC to load the registers with pre-selected frequencies for the three outputs, like 3.5 MHz, 7 MHz and 10 MHz.  This could then be used for crystal replacement in applications like the LF Converter kit ?  But there are a LOT of registers - again, time to read the manual !

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm