Scan tab - voxo22/hackrf-spectrum-analyzer GitHub Wiki

Gain (LNA/VGA)

The gain slider automatically combines the LNA and VGA sliders. The LNA and VGA sliders directly control the parameters of the hackRF input circuits. The optimal setting is LNA 40 dB and VGA < 18 dB. If the signals at the input should have a higher level, reduce the overall gain. If the signal is still weak with this setting, turn on the RF amp, or use an external preamplifier. Warning: the overall signal strength at the hackRF input must not exceed +10 dBm, in case of activated RF amp max -5 dBm!

RF amp

This checkbox controls the internal hackRF's RF amp. Use in case of analysis of very weak signals (RF amp should add extra approx. 14 dB of gain). Warning: the total signal strength at the hackRF input must not exceed +10 dBm, in case of activated RF amp max -5 dBm!

BiasT

This checkbox turns on antenna power. 3.3V DC will appear on the antenna connector.

No DC

Use this checkbox to get rid of spur artifacts in spectrum chart and waterfall. They are usually displayed as amplitudes (infinite vertical lines on waterfall) that do not change over time and do not actually exist in the signal. They do not disappear even after disconnecting the signal or antenna. Usually their position changes with different frequency range settings. They can be various remnants of harmonic signals of the hackRF's internal clock.

Spur artifact filtering takes a fraction of a second to load a representative evaluation sample. If artifacts appear even with the checkbox checked, uncheck it and check it again. This is usually necessary after switching frequency ranges.

Spectrum type

These checkboxes enable and disable individual types of curves on the spectrum chart. Enabling some curves also activates other possible settings on the Parameters tab that are related to them. 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.

All curves can be displayed simultaneously.

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.

Markers

Markers display a small arrow on the spectral chart at the point where the maximum amplitude of the entire displayed frequency range is currently located. The amplitude and frequency values ​​are also listed above the arrow. You can select a marker for the green PEAK curve or the red MAX HOLD curve. The marker checkbox is only displayed if the corresponding curve is displayed.

Resolution bandwidth (RBW)

RBW is the basic parameter for the resolution of the spectral chart display. It represents the smallest unit of resolution of one sample (FFT bin) on the graph. For example, for a frequency range of 40 MHz and an RBW of 50 kHz, one point on the graph represents a bandwidth of 50 kHz, and there are 800 of these points (FFT bins) on the graph in total (0.05 MHz x 800 = 40 MHz).

The smaller the RBW you set, the more detailed the graph will be. 3 kHz RBW is suitable for displaying small frequency ranges. However, this resolution can be very unclear for larger frequency ranges, so choose a larger RBW. The RBW setting does not affect the scan speed, but it does affect the total number of points on the graph, i.e. memory usage.

If you use the mouse to zoom in/out on the graph, the RBW will be automatically set to the optimal value. In this case, set the required RBW value manually.

If you use Frequency presets, it is necessary to enter the desired RBW value for each defined frequency range in the Presets.csv file, to which the spectrum analyzer should be set after starting the scan.

Frequency shift

The frequency shift parameter is used in connection with the use of an up-/down-converter at the hackRF input. For ranges around 0-30 MHz, an up-converter is usually used (e.g. SpyVerter has a shift of 120 MHz, for example, so we need to shift the frequency axis back by -120 MHz). Satellite TV LNBs are down-converters that shift signals with frequencies of 10.7-12.7 GHz to 950-2100 MHz. Here, a positive shift must be set so that the X-axis shows the correct signal frequency.

If you use Frequency presets, it is necessary to enter the desired Shift value for each defined frequency range in the Presets.csv file, to which the spectrum analyzer should be set after starting the scan. Use 0, if no shift is present.

Amplitude offset

The Amplitude offset slider shifts the Y axis of the graph of all curves down or up by the selected number of dB. It is used especially if you want to use the entire spectrum dynamics for different frequencies in a comparable way. For example, HackRF has different sensitivity at different frequencies, so certain sections of the graph may appear slightly shifted higher or lower on the Y axis. The RBW setting also affects the shift on the Y axis. The Offset slider will help correct this situation.

If you use Frequency presets, it is necessary to enter the desired Amplitude offset value for each defined frequency range in the Presets.csv file, to which the spectrum analyzer should be set after starting the scan. Use 0, if no offset is present.

Power calibration

The power calibration slider is used to correct the display of the total power flux density for the displayed spectrum in the information panel in the lower right part of the waterfall and also in the DATA record, if used. The individual powers in dBm are summed for each FFT interval. The power flux density is calculated from the summed power, which allows an approximate calculation of the RF field strength.

Use the Power Calibration slider to set the power flux density value to match the current calibration value of a known source or calibrated measuring instrument. Any further scans of the spectrum analyzer will then display approximately the correct power flux density value of the displayed spectrum.

Note: however, with each change of frequency range or antenna change, the current calibration will probably be invalid and will need to be set / noted again.