There are two variants of this:
- An aircraft symbol is visible right at the center of the display (for moving-map-style displays) or aft (LED-style displays) with a small distance indication.
- A non-directional target is shown with small distance and/or strong signal and at the same altitude. On PowerFLARM Portable, this would show as a small circle around the ownship symbol.
In both cases, the problem is due to the PowerFLARM displaying the signal from the own transponder (Mode-C/S or ADS-B). Normally, these signals are filtered out automatically, but there are conditions under which this fails.
The following points should be verified:
- Is the 24-bit ICAO aircraft address configured correctly on PowerFLARM? In the FLARM configuration tool, the entry "ICAO 24-bit aircraft address, hexadecimal" should be verified. The address must be entered as it appears in the aircraft documents. It consists of 6 characters, 0-9 and a-f. The case does not matter.
- Is the "Transponder type" set correctly in the FLARM configuration tool?
- In some rare cases, the own transponder may be configured wrongly. On some models, the programmed ICAO address is visible at startup.
- Ensure that the "Mode-C filtering method" is set to "Aggressive". Removing/filtering own Mode-C signals is more difficult than Mode-S or ADS-B and more aggressive algorithms may be needed.
- Furthermore, "Mode-C target processing" can be disabled altogether. This is the default setting in the configuration tool. In areas where Mode-S adoption is widespread (e.g. Europe), this is the recommended setting in any case, as the Mode-C signal is simply not needed.
If the above items do not help and it's strictly necessary to enable Mode-C processing, it may help to move the 1090 MHz receiver antenna of PowerFLARM into line-of-sight of the own transponder antenna. If the antennas are shielded from each other, e.g. by being on different sides of the aircraft (top vs. bottom), PowerFLARM may think that it's another aircraft because the signal is too weak. Just make sure to always keep at least 30 cm between the antennas.
Finally, note that the "1090 antenna calibration value" setting does not have any effect on the filtering. This setting only affects the calculated distance to aircraft which are already not filtered out.
Also see How is non-directional (transponder) traffic treated?
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