I have a device that has an internal TCXO. I want to feed it with an external OCXO, but I don't want to completely replace the TCXO. Here is the scenario. On initial power on, or after a power loss, I want the internal TCXO to be used. Once the OCXO is up, I want to switch to it. How could this be done easily and cheaply? Joe Gray W5JG