Does anyone know if the FA Filter has a polarity to it? Ie, is there a specific side that the antenna should be connected to? The reason why I ask is I saw a 20% reduction in planes while using the filter (for about 2 weeks). After removing it, the very next day my numbers went back up.
Granted my setup changed slightly in the process. Without the filter, I use an maje MCX to female RG6 adapter which is then connected to 10ft of RG6, which is then connected to my antenna. With the filter, I used an male MCX to male SMA adapter, then the FA filter, then a female SMA to female RG6 adapter, then my 10ft of RG6 and antenna. So it is possible that the the loss is a result of the different adapters. I could put those back in and just remove the FA filter. However, I thought I would check first to make sure that the filter not just installed backwards.
Otherwise, is it possible that the filter is not working properly because my impedance is off and/or it is positioned improperly (ie should it be connected directly to the antenna? Lastly, I am using a home-built ground plane antenna. Is the FA filter only really intended to be used with the FA antenna?
Fairly sure there’s no directionality to the filter.
Adding the filter to the system is not free - it introduces some loss of signal even in the bandpass region. A filter is only generally going to be useful if you have strong interfering signals from e.g. nearby cell towers; in those cases, there’s a big benefit to silencing the interfering signals before they swamp the dongle’s input stages, which outweights the small loss to the ADS-B signal. But if you don’t have strong interfering signals then you’re just losing some ADS-B signal strength for no benefit.
I found this is on Amazon’s page (http://www.amazon.com/dp/B010GBQXK8?tag=fligh01-20) for the FlightAware filter:
The SMA male connector (to the right of the image nearest the end of the "Flightaware logo) connects to the receiver. The SMA female connects to the coax cable from the antenna.
I do not believe the filter is directional, but I have not tested it. Someone posted awhile back that they installed it opposite the information dblake mentioned above and it still works.
More likely it is the additive loss. You didn’t mention your antenna type, but in your setup without filter the RF path impedance is 50 ohm downstream of the antenna. With the filter you’re converting between 50 ohm and 75 ohm at least twice, at each end of the filter with your RG6 cable, which will incur loss.
