OCXO/Si5351A + Arduino = frequency of output signal iscycling changes #problem #ocxo #si5351a


My thoughts are its scope hookup has issues and is adding in extraneous noise that
the DSO is trying to sync on.  Since the signal is both amplitude and phase I'd suspect
outside sources getting into the hookup.

I see this all of the time when people new to scopes do not understand how to ground or otherwise
hook up a scope so they do not  introduce spurious signals.  That 8 inch lead from the scope
probe is also an antenna.  Around here I can see 20-50mV of RF from a broadcast station
maybe 4 miles away with that led connected to the tip.

LIkely the 5351 signal is stable.   Though its possible that the MPU is updating it with a range
of possible signals out so you can be seeing the frequency actually chance.   If the code is as
supplied likely not the case.

So if I had to guess and the images sent help not, Id say your seeing a broadcast station
getting until the scope via the probe.



This is hyterodyne,  and this jumping I got from CLK1
Thank you Steve!

Steven Weber

So, what are we looking at there? The output of the Si5351 or the output of your heterodyne mixer?  Either way, unless the signal goes through a band pass filter, there will be significant harmonic content which can cause the fuzzy trace.


Steve KD1JV


The jumpiness on the oscilloscope might be harmonics and other signals, perhaps digital signals, leaking into the output.

As the extraneous signals go in and out of phase with the desired signal, instantaneously adding and subtracting from the desired signal, the trace on the scope will demonstrate the jumpiness you're seeing.