1.3 Bandpass Filter
As SDRs are not specifically made for our desired frequency they will pick up a lot of other signals on neighboring frequencies. This will lower the performance significantly and it may be impossible to pick up the desired signal at all. A bandpass filter is a good measure to help with that problem. An optimal bandpass filter reduces the signal strength on unwanted frequencies while letting our desired frequency through to the SDR without much loss. Sadly there is a big difference between different filters. This is why it is critical to buy a proven one.
#ADS-B
While there are SDR dongles with integrated bandpass filters for 1090MHz ADS-B reception available, a dedicated filter is a very good addition to the setup. The internal filters are based on a very small SMD chip which contains most likely a SAW filter. The dedicated Filters can be based on this chip or on a capacitor and resistor design.
This filter is based on a capacitor and resistor design. This version is specifically built for 1090MHz and very narrow which gives the best result without being expensive. If you can get one just buy it.
This filter is based on an SMD chip. While it has an slightly higher insertion loss than the Flightaware ones, it is much narrower than the Flightaware Filter dual band version. Price is equal to the Flightaware one, so it is our second choice if the singleband Flightaware filter is not available.
This filter is based on a capacitor and resistor design. This version is built or 978MHz UAT and 1090MHz ADS-B, which makes it much wider. Nevertheless it is very effective and can improve your reception quite a lot.
All the other 1090MHz filters we have seen are based on the SMD SAW and some of them may even use a knockoff part which would be the only way to explain the very bad performance.
While there may be other good filters out there, we are not willing to pay multiple times of a proven filter just to find out.
While there are not many options for affordable AIS bandpass filters, the AIS reception usually works very well without a filter. If you can obtain an SDR with an integrated AIS bandpass filter that is the way to go.