What limits the frequency in the linked schematic is the 25ns rise time of the counter input on the ATmega328 micro on the Arduino.? It could be redesigned so the counter input measures one of the other clock outputs of the Si5351 set to 1/8 or 1/16a of CLK0.
That would require a code change for the Arduino and the Si5351.? ?Another solution is to use a micro with a faster hardware input counter and clock frequency, like the 133MHz clock on the RP2040 on the Raspberry Pi Pico, or the 150 MHz clock RP2350 micro on the Raspberry Pi Pico 2. ?
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N0YWB