FlightAware Discussions

Antenna Filter advantages

Appreciate FlightAware market two ADS-B tuners, one with inbuilt filter and the other without. Also aware a separate FA filter can be purchased.

If purchasing a new tuner are there any detrimental effects of using a device with inbuilt filter if the filter wasnt really required?

I understand filters may be beneficial in heavy residential areas where background electronic signals could interfere with ADS-B data but less so in rural areas.

Geoff

That’s a wrong impression. Mobile phone towers are everywhere, those are the biggest source of interference.

The filter in the ProStick+ is never a problem, it’s behind the LNA.
A filter coming directly from the antenna can reduce reception of weak signals.

Basically you’ll just have to test what gives you better reception.
Note that the ProStick+ internal LNA is susceptible to interference as well, so many people get more messages/s with an external filter in front of the ProStick+.

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That is interesting, so, effectively two filters.

I’m often amazed at how good the system is at picking up signals when antenna not ideally placed.

I’ve got mine by a NW window but pick up aircraft approaching Heathrow from SE direction up to 12 miles away.

Geoff

In rural areas the cellphone towers (transmitters) often transmits with higher power than those in residential areas since there are fewer towers around and they need to cover larger areas. Same with broadcast FM-radio and terrestial TV-services.

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A low loss filter between the antenna and the ProStick SDR generally won’t block weak 1090 MHz signals because the signal to noise ratio (SNR) is not limited by the receiver noise figure.
In our FA receiver systems the SNR is chiefly limited by interference and distortion.
A highly selective front end filter ahead of the LNA certainly helps at my urban site.
In a test I found adding a few dB of RF attenuation between the filter and LNA made no difference in the aircraft counts or distant track performance.

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