OTA signal Strength uV

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In the analog world you need to be able to pick up between 50uV to maybe 500 or 1000uV of of signal from a particular station (frequency) to get a useable picture.
I have two somewhat related questions:
1.) What is the min. signal strength in uV required to lock a digital signal OTA HDTV?
2.) I realize this will vary somewhat depending on what particular set top box is in use - but at what level of incoming RF signal  will you overload the RF input of a STB. I haven't noticed this spec for any of the STB I've looked at