Hi Ho!
Seems that the frequency counter leaks a 10 MHz signal to it's input.
I was looking at a spectrum and noticed a 10 MHz signal where none should be.
See attached screen-dumps.
I used my SDG2kX to generate a 100 MHz sine wave at 100 mV rms into 50 ohms. In the first attachment
that is fed into a DSA815 and only shows a harmonic at 200 MHz. In the second attachment I placed
a T attachment on the output of the SDG2kX and fed one side to the DSA815 and the other side back
to the counter on the SDG2kX (its on the back). Wow, look at all those remnants.
The log scale for frequencies (x axis) shows just how much is being generated. It seems as
though the counter is acting as a mixer of its internal 10 MHz reference and the 100 MHz being
generated by the SDG2kX. If I zoom in one of those peak frequencies, then they are pretty well exact
multiples of 10 and/or 100 MHz.
BTW the SDG2kX counter correctly reported 100 MHz as the frequency. Reporting the "frequency
deviation" as 900,000 ppm seems a bit strange, as though Siglent assume the counter will only
be used to measure 10 MHz from another source (e.g. the DSA815 has a 10 MHz out and it
showed ~ 0.1 ppm .)