The filter/LNA project is designed to improve the ADS-B Reception of a RTL-SDR USB Dongle. More on operation of the dongle and reception of ADS-B can be found at <http://www.reddit.com/r/rtlsdr>. There are three elements extrenal to the software/sdr that this project emcompasses: the antenna, frontend filter, and LNA. ANTENNA: ---------- Any antenna that covers 1090MHz can be used for this purpose. I am using a design found here: <http://www.sprut.de/electronic/pic/projekte/adsb/adsb_en.html#antenne>. FILTER: ---------- Files for the filter design are contained the in the Filter directory. There are two versions of the filter layout. The "standard" filter, and filter_slant. Filter_slant is the same as filter, just adjusted so the connectors are in a line in the X/Y Plane. This will allows for a narrower PCB, and keeps any forces in the same direction, ie. doesn't try to pull the connector off to the side. This is good for an antenna mounted design. The main filter directory contains the .dxf files for the filter design. You can use a free dxf viewer to see the filter and print it. be sure that if you print the file to etch a filter, that it is 1:1 scale, otherwise the frequency of operation will be shifted. Eagle specific files are contained in the eagle specific sub-directory. The script (.scr) files can be used to generate the filter in any board layout. If you're sending out the PCB for fab, make sure there is no solder mask over the PCB area, as this can affect the filter's frequency response. You can take the .brd files and send them directly to OSH Park <http://oshpark.com/> for fabrication. Filter performance can be seen in the Test_Data sub-directory. LNA: ---------- The LNA design is still in the works, but is based on the design shown here: <http://www.lll.lu/~edward/edward/adsb/preamp/ADSBpremap.html> and modified as per the instructions of Dr. Ken Filardo, KA0THK CC-BY-SA N0RC, 2013.