I was having the same problems with no signals appearing with the default settings.
I was finally able to get the sdr# working with mine.
In other words, SDR is like a very fast sound card with the speaker and microphone replaced by an antenna. Just as a sound card in a computer digitizes audio waveforms, a software radio peripheral digitizes radio waveforms. It is similar to the software-based digital audio techniques that became popular a couple of decades ago. SDR is the application of Digital Signal Processing to radio waveforms.
Further, it does not require the use of capacitors and resistors, as the software-based filtering algorithms can be utilized to select specific frequencies. What this means is that the functionality is modified or changed by software alone, eliminating the need to make any physical changes to the hardware. Software defined radio (SDR) is a wireless communication device in which the transmitter and receiver modulation/demodulation occurs in software. SDR Training with HackRF, Advanced Software Defined Radio Training