Adjecent channels confusing DOA estimation

1

Earlier today participated in a radio direction finding training exercise, with 4 narrow-band FM transmitters. I tried to use the Kraken to locate one transmitter that was 15 kHz away from other known transmitters, however, the Kraken kept getting DOA fixes for the transmitter on the wrong channel, leading to a heat map on the android app that clearly showed where the ‘wrong’ transmitter was.

To double check I tried erasing the collected data, and ensured I had correct frequency set in the Kraken raspberry pi server, but the next batch of data generated the same heat map. In the spectrum view, the two transmitters were visually distinct.

Is there any way to adjust the frequency selectivity of the DOA algorithms to handle a scenario such as this?

2

This might be a case where increasing the “FIR Order Factor” in the VFO settings card might be useful. The FIR Order is set relatively low for performance reasons, but if you have a much stronger adjacent channel, increasing the FIR order may be necessary.

If you increase the FIR order the channel selectivity will improve.