Spectrum chart - voxo22/hackrf-spectrum-analyzer GitHub Wiki

The spectrum chart shows the relationship between frequency and amplitude of the signal. You can choose from 4 different curves:

• REALTIME - white
• PEAK - green
• AVERAGE - yellow
• MAX HOLD - red

The REALTIME curve shows instantaneous samples that were captured by hackRF and since it is a very fast, constantly repeating process even hundreds of times per second, it can be very difficult to read in the case of very short pulses. Therefore, other curves are also available, such as:

The PEAK curve shows instantaneous samples, to which a holding algorithm is applied, which you can set according to your own requirements. The Peak curve can gradually decrease if the same or higher value is not repeated immediately after the peak (maximum) is captured. It is therefore ideal for monitoring the course over time, which everyone can adapt to their own needs. The PEAK curve is the source of statistical calculations, the results of which are in the lower right corner of the Waterfall. By turning off the PEAK curve, this data will no longer be displayed. At the same time, some PEAK curve data is recorded if DATA recording is turned on. Therefore, after turning off the PEAK curve, it is not possible to record DATA to the log.

The AVERAGE curve shows data that is the average of several PEAK curves. The number of iterations can be set in the Params tab. At the same time, the AVERAGE curve can be "moved" along the Y-axis, as in some cases it can undesirably hide below the -100 dBm limit.

The MAX HOLD curve shows the maximum values ​​that the PEAK curve has reached, but these are remembered on the screen.

The curves can be shifted within a certain range along the Y axis using the Amplitude offset slider.

All curves can be displayed simultaneously. The speed of drawing the curves on the screen depends on the total frequency range. Their detail depends on the total number of points (FFT bins), each of which is a representative of a separate sample of the amplitude level at a given frequency.

The more points, the more detailed the graph, but at large frequency ranges also less clear. It is ideal to achieve a number of points (FFT bins) that corresponds to the width of the display on your screen. For example, a screen with a resolution of 1280 horizontal points has an ideal display with a number of samples (FFT bins) of 1000 - 1500. Information about the number of FFT bins is displayed in the info window at the bottom right of Waterfall. The total number of FFT bins on the graph is directly dependent on the RBW parameter. By adjusting this parameter, you can influence the detail of the curves.

A special case of display is "PERSISTENT", which expresses the representation of certain frequencies over time. Individual times of representation are color-coded. The longer a signal is present at a certain frequency, the "redder" the coloration. Sporadic signals are dark blue to black.