Optimal / maximum RF input level
I am not sure if there is an easy answer to this question, but what is the optimal maximum RF input level? Obviously you don't want A/D overload and clipping, but should the signal level be kept even lower than that, perhaps to avoid any nonlinear regions of the front end amp?
-15dBm at 50 Ohm would be 56mV peak.
20 dB of LTC6401 gain, data sheet again, and 2 dB of LPF loss, an estimate, would produce 18 dB gain ahead of the conversion. This net gain would turn a sine wave of 44.5 mV rms ( -14 dBm in 50 ohms) at the SMA connector into 1 V p-p at the LTC2248 ADC. I'm guessing that the OV indicator comes on when the instantaneous input exceeds this level, which agrees closely with what we all measure.