Fig. 6
From: Software-defined radio-based HF doppler receiving system
a Output responses of the analog and digital receivers to input signal level (blue: digital, red: analog). The left-hand and right-hand vertical axes show the digital and analog output level, respectively. The black line shows the ideal linear response. b Transmission characteristics of the filters of analog and digital receivers using the 8006 kHz channel. The blue shaded region shows the bandwidth of the frequency range of the provided Doppler frequency data in the web page of the project (from – 4 to 4 Hz)