@abcd567 asked this week for a more complete one to one test of different filters. so - here we go:
a picture of what will be tested - the results follow as soon as finished.
HERE WE GO - MY RESULTS:
the site is located on the country side about 25 miles south of munich/germany. all tests on the same jetvision a3 antenna, rtl-sdr dongle and raspberry pi2. while test ran always about 200 aircrafts were in receiver range. pi + dongle used ran for 3 hours before test started to have same temperature from start. gain was fix set to 50. if you watch the scans not only look for noise but also for 1090mhz signal - because it’s all about signal-noise-ratio (snr).
- for most sites the uputronics saw-filter/lna is the best bang for the buck
- if noise at your site is somewhat heavier over the full range the uputronics ceramic-filter/lna is the best chioce
- for those with really heavy noise over the whole frequencies a cavity filter in front assisted with the uputronic lna with ceramic filter behind is the way to go. the jetvision cavity filter has extreme low passband attenuation (0.5db) - that’s why this is the only filter to use in front of an lna
- the flightaware filter has excellent attenuation far below and above 1090mhz - but unfortunately totally fails at all frequencies very close to 1090mhz and those are most often the biggest challenge for the receiver
edit: one thing i forgot to mention is that using the cavity (3-pole) filter some aircrafts behind the alps i get longer distance messages from. maybe this is because the passband attenuation is extremely low while mostly all noise is filtered out - and because of this the receiver (dongle) has a bigger chance to find and decode those faint signals …
you can plot your own scans following these steps:
install needed software:
sudo apt-get update sudo apt-get install git build-essential cmake libusb-1.0-0-dev python-imaging git clone https://github.com/keenerd/rtl-sdr.git mkdir rtl-sdr/build cd rtl-sdr/build cmake .. make rtl_power wget https://raw.githubusercontent.com/keenerd/rtl-sdr-misc/master/heatmap/heatmap.py chmod +x heatmap.py
now anything you need is installed and you can e.g. do those two scans:
sudo killall dump1090-mutability ./src/rtl_power -f 800M:1400M:300K -i 10 -c 50% -g 50 -e 20m -F 9 >scan_800_1400.csv ./src/rtl_power -f 24M:1700M:1M -i 10 -c 50% -g 50 -e 40m -F 9 >scan_24_1700.csv
when both scans are done - plot the graphs:
./heatmap.py scan_800_1400.csv scan_800_1400.png ./heatmap.py scan_24_1700.csv scan_24_1700.png