Usage cautions - voxo22/hackrf-spectrum-analyzer GitHub Wiki

After starting, the analyzer is set to a gain of 52 dB (LNA 40 dB + 12 dB VGA). If you do not know how strong the measured signal is, do not connect the antenna or signal source before turning on the hackRF or before starting the analyzer. First, start the analyzer and set the total gain to 24 dB. Then connect the antenna or signal source to the input. Ideally, you can measure the exposure using some broadband meter and then connect the antenna to the hackRF, if cumulative field strength is not more than e.g. 100 mW/m². Be extremely careful in case of connecting to long wire antenna w or w/o balun! Or, when connecting directly to the signal source by cable without any attenuator!

Do not forget that the maximum power that you can connect to the hackRF is +10 dBm (without turning on the internal RF amp). Using the RF amp, it is only -5 dBm, but I would be careful and not exceed -10 dBm (i.e. 0.1 mW). It has happened to me a few times that the RF amp blew up when I carelessly connected powerful sources. Nothing will help then, except for the difficult amp replacement on the hackRF board. You should be careful, for example, if you connect hackRF and the analyzer to even a small antenna that is less than 100 m from the nearest mobile network transmitter. This situation can also occur in your apartment and you can easily destroy the RF amp. If you still need higher gain on certain bands and you are near a strong RF field source, use an external preamp (e.g. 20 dB one that comes with hackRF in some cases) and never turn on the internal RF amp! It seems ideal to use a band pass filters to filter out unwanted signals.

So the RF amp is intentionally not turned on when starting the analyzer. NEVER turn on the internal RF amp unless you are sure that there is not too strong signal on the entire spectrum. The analyzer only scans a part of the frequency spectrum and you may not suspect that there are high signal intensities on another part of the spectrum. The maximum at the hackRF input applies to the entire frequency band, cumulatively.

The maximum usable amplitude dynamics is about 70 dB. This is the section between the lower level, calibrated as -100 dBm, and the maximum that the hackRF is able to process without distortion, which is about -30 dBm. In this interval, the dynamics are almost linear, but above -30 dBm it is already significantly limited (it also depends on the hackRF board version). Do not be confused by the amplitude shift when changing the gain or offset, the dynamics do not depend on the offset or gain settings.