Also known as Direct Sampling, to receive HF the tuner is disabled and the IF mode of the RTL2832 is activated. Unless you have a RTL-SDR Blog V3 or V4, you must modify the dongle, more information available here [ link].
You must select the correct HF Mode option, see Options below.
Note: RTL-SDR Blog V4 is based on the R828D and has a built-in upconverter instead of using a direct sampling circuit.