FlightAware Discussions

ADSB Blue filter necessary?

I saw a picture of a ADSB Pi set up and I noticed they had a Flightaware Blue dongle and also had the Blue filter installed. Since the Blue dongle already has the 1090 filter is the external filter necessary?

Short answer is in some circumstances, yes.
The filter in the blue ProStick plus is after the preamp. If you have strong enough signals from things such as mobile phones, PMR radio, DAB and FM radio, you can overload the preamp.
Here I need an extra filter. See this from a couple of years ago.

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I’m getting ready to install my filter. I have learned over the past several years to keep RF noises down to a minimum and I actually moved my Piawaare and ACARSpi to a closet out of the way from any type of RF noises. My Elads FDM-s2, SDR Play, and Airspy reside on another part of my house and fed by a USB3 repeater cable and they work very well because the antennas reside outside and away from my house in a low noise environment.

It really depends on your location and environment.

I am in Germany so beside the FA pro plus stick i decided to spend another 20 Euro for the dark blue 1090MHz filter.

The result was somewhat disappointing. No real improvement, i needed to increase gain by two steps and the result was finally similar.
So if you’re already in a perfect environment, it’s obviously not necessary. Geographical limits cannot be eliminated with it.

You might give it a try, but it could be that it does not bring improvement.

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:+1:

Example:

  • At @foxhunter’s location, Filter did not bring any improvement as his location has low RF noise environment.

  • At my location if I remove the filter, the reception drops to 10%, as my location has very high RF noise environment.

Please see following scans (with & without interna/external Filters) which I conducted about 6 months ago at my very RF noisy environment. I carried out scan as per following guide.

Spektrum - How-to Speedily Scan RF Noise in band 24MHz ~ 1800MHz

The results of scans are below:

The scan 1 shows RF noise picked by antenna and processed without any filter , The scans 2 & 3 were done with filters, and show how filters remove this noise.

Scan 1 of 3 - FA Antenna + Generic DVB-T (no internal or external filter)

Thumb-Generic DVB-T
CLICK ON IMAGE TO SEE LARGER SIZE

Scan 2 of 3 - FA Antenna + ProStick Plus (Only Internal filter of ProStick Plus. No External filter)

image
CLICK ON IMAGE TO SEE LARGER SIZE

Scan 3 of 3 - FA Antenna + ProStick Plus (with internal filter) + External Filter (FA Light Blue)

imageimage
CLICK ON IMAGE TO SEE LARGER SIZE

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I added my filter back. It’s the light blue filter I bought a few years back when I had started with the orange dongle. It’s hard to tell if I needed it or not but I figured why not. Hard to tell because usually, the weekend’s air traffic is sometimes unpredictable. I think that my next investment is my 978 antenna. I have a home-brewed cantenna but I don’t think it’s not as good as it should be. Right now the FA 978 antenna is sold out on Amazon.

ADBExchange has a 5.5dBi 1090/978 N-Type Female Antenna available. However that would mean you need a splitter.

I’ve been using one with great success since early January.

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I am tempted to get it.