IK1IYU recently mentioned, that it
"Looks like the easiest pluto sdr tcxo removal….is NOT removing it at all. According to Analog Device Pluto schematics, pin 1 of the tcxo is an Enable/Disable pin and simply grounding it should disable it."
But if pin 1 is not connected statically to GND, an automatic clock selection can be realized with little effort.
This is made possible by TI's SN74LVC1G125 chip, which has a low-active enable input and accepts input signals up to 5V with 1.8V VCC. So a single Si-npn transistor provides automatic source switching, a pull-up resistor is not necessary.
The tested circuit diagram is attached.
The advantages are:
The original XO does not have to be removed.
The Pluto still works even if no external clock is fed in.
And last but not least, accidentally too high Clk levels or ESD no longer directly endanger the heart of Pluto.