I’ve already share some picture of my filter in another topic “Do I Need A Filter?” but I think this project deserve is own topic.
After some internet search and following some advises from this forum I’ve decided to build my interdigital filter. The filter was built using double clad PCB and some brass tubing. Tuning was done using the POOR MANS SPECTRUM ANALYZER WITH AN RTL-SDR AND NOISE SOURCE.
Finally I had the opportunity to test the 3 settings (no filter, FA filter and home made filter) and here is what I’ve found:
I believe the Home Made Filter has a high insertion loss and that’s the reason the messages >-3dBFS are kept low while gain isn’t at MAX, but still is better than not having a filter.
I did compared my FlightAware statistics with the nearest 3 sites (one of the sites is a FlightFeeder). Not a very accurate method since the receivers don’t cover the exact same area, but it was the close I could get. Compared with the other sites the number of flight doesn’t change that much with all combinations (filter/gain), however the number of positions does.
Besides those big antennas in line-of-sight I also have 8 cell towers in less than 1km radius, making the use of a filter mandatory.
You can download the file that contains information about gain, signal level and the comparison with the other sites from this link ADSB_Gain.xlsx
I’ve already plans to build a second filter, this time I will do it with more precise measurements and extra care to keep everything aligned. Hope that the next filter together with the “refurbished” Jetvision antenna will increase the number of positions.