By necessity the modes used have a narrow bandwidth. CW is the norm, but there is some use of the new PSK31 as well as some more exotic data modes. There are two programme which are popular. The programmes takes the received audio and analyses it by performing a fast Fourier transform. The resulting data is displayed on the computer's monitor as a plot of frequency against time.
Signal strength is shown as a variation in colour.
Spectrogram can be downloaded free of charge from the Internet. When we receive a particular mode, the radio will have a filter to match its bandwidth. Frequently, CW operators use 500 or 250Hz filters. However there is a limit. Spectrogram can simulate an extremely narrow filter of less than 1Hz wide and this allows you to receive the CW when it would normally be many dB's below the noise level if received with an SSB filter.