I have a pic in the VLF band at 1.5 kHz. What would be the origin of this peak?
The graph was obtained by running
display_qt in Linux from a laptop.
display_qt is a GNU Radio example program. It does not display any actually existing electromagnetic signal but internally generates a 1500 Hz sinusoid.
The code creates a sine source and a noise source,
// Source will be sine wave in noise src0 = analog::sig_source_f::make(rate, analog::GR_SIN_WAVE, 1500, 1); src1 = analog::noise_source_f::make(analog::GR_GAUSSIAN, 0.1);
then sums them and sends that to the displays.