Luckily, your wonderful graphs1090 makes testing easy in this 4-step sequence:
- Turn on the leaky converter to reproduce effect of the interference.
- Insert 15MHz bandpass filter between the antenna and the FA blue stick to test noise level change.
- Remove the filter to reconfirm high noise level.
- Turn off converter to reconfirm normal noise level.
That’s exactly why a narrowband filter helps suppressing broadband noise. In that big rod vs short wire antennae thread, LawrenceHill points out that the blue stick’s built-in filter is behind the preamp. My high-gain rod is picking up a lot of broadband noise to overload the preamp. After applying the narrow-band filter, the station currently with the rod began to outperform the wire antenna station even though the rod is in a really bad position.
Broadband means that energy is spread out, therefore energy in 1090 MHz ± 7.5 MHz is small. If digital video leakages has a strong peak near 1090 MHz as I first feared, the filter will not be useful. Of course, this source is too close, so the filter’s protection is limited. I’ll ask for another converter and see if it has better shield.