FlightAware Discussions

Impact of filters on quantity / distance of aircraft

New to Piaware (9 days in). I am in urban setting just north of downtown Dallas. I ran for the first seven days with the FlightAware ADS-B Dual 978 MHz + 1090 MHz Band-Pass SMA Filter installed directly off my Pro Stick Plus. After that, I decided to remove the filter and see what happened with the antenna attached directly to the Pro Stick Plus (everything else remained the same). Without the filter, my aircraft reported per day doubled, position reports went up 5x, and I went from seeing almost no traffic outside the 50-mile ring to seeing things out to 200-miles and beyond in every direction.

BUT without the filter, almost all the close, low-level traffic has gone away. I’m about 5 miles from Dallas Love Field, and I was getting incredible detail of departures and arrivals until I removed the filter. I still see plenty of low level traffic coming in / out of DFW without the filter (about 20 miles away). I’d love to understand “why” and find out if there is a way to get the best of both worlds?

My setup is:
Raspberry Pi 4 B running PiAware 4.0
FlightAware Pro Stick Plus
FlightAware ADS-B Dual 978 MHz + 1090 MHz Band-Pass SMA Filter
DPD Productions ADS-B Vertical Outdoor Base Antenna
RG8X Coax Cable (20 ft. N Male / SMA Male)

Try reducing gain.
To check current gain setting
sudo piaware-config --show rtlsdr-gain

To set gain to say 43
sudo piaware-config rlsdr-gain 43
sudo systemctl restart piaware

Try different (random) gain values listed below and observe for some time performance at each setting. This is a trial and error process.

-10
49.6
45
43
38
35

9dBi is quite impressive. Couple that with low loss coax and an amplified dongle and it’s not surprising strong local signals are overloading the front-end. Given the relatively low insertion loss of the FA filter, the magnitude of the performance change is quite surprising. I’d suspect the patch lead you were using between the filter and dongle may have a fault.

As above, playing with the receiver gain and searching for the “sweet spot” is your best $0 approach.

I have DPD antennas for 978 and 1090Mhz. Both work really well.
You may want to upgrade your dongle to the Airspy(A mini is more than sufficient). You can only run one per RPI, however, it has a larger dynamic range so can receive louder and quieter aircraft, using the same gain setting, compared to the RTL-SDR/FA dongles. They do require an amp between the filter and dongle otherwise they are a little deaf. The amp can be powered by the Airspy.
I have uputronics and rtl-sdr filters. The uptronics is not great in noisy environments.

uputronics amp/filter.


You can buy the airspy and uputronics amp/fitler in the US at the site below

rtl-sdr amp/filter.
https://www.rtl-sdr.com/buy-rtl-sdr-dvb-t-dongles/
scroll down to RTL-SDR Blog ADS-B Triple Filtered LNA

I run two airspys on 1090Mhz. One on an RPI4 and the other on an Odroid XU4.
I have so much noise in my area that I need to use cavity filters on all of my receivers (978Mhz, 1090Mhz as well as 14xMhz etc).

Thank you all for the wonderful suggestions, steps, and links. This is exactly the kind of advice and experience I was looking for. I’ll be sure to post back again later once I have had an opportunity to explore all this.

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