Hi all, I just found this forum yesterday, but am quite the enthausiastic hobbyist/student myself. I currently got lots of packages on their way to me, (got one sdr with simple antenna, two more sdr's on their way + power amps + inserters etc). love all the info in this very usefull thread! When i get back from holiday (currently in france) I'm going to solder a (few) spider-tenna(s). (i'm an ex-electrical engineering student, currently studying computer science/software engineering)..........
WELCOME ABOARD! Take a plunge into the world of DIY ADS-B
Spider 8-legger is a good antenna to start with. Gives good results, and is simple to make, if one has moderate to good soldering skills.
For those who don't want to bother for soldering, 4 legs, fixed to 4 screw holes of connector SO239 is an easy choice. The 4-legger also works good, but somewhat inferior to 8-legger.
After your system takes off, you can start building & trying other types of antennas, starting first with simple ones like Dipole & Cantenna, then moving on to more difficult collinears like CoCo, Franklin & Coiled Whip.
Don't worry about Amplifier's quality just because it is cheap. Most Satellite amplifiers are good for ADS-B, and are quiet cheap. I have purchased 3 pieces of RCA D903 amplifier, 13-18 dB, during last 2 years. These cost only $4 each, but give very good performance.
Power supply is also not critical. These amplifiers are rated to work at any voltage between 13V - 18v DC, and have good voltage tolerance. My power supply, rated for 15V, measured 20V with a multimeter, and is powering my amplifier for 2 years without any problems. I purchased a cheap power supply which seems to have a poor regulator and a heavy iron cored step-down transformer. A better option is a switching power supply which does not have bulky & heavy transformer & has far better voltage regulation. Since the power requirement of these amplifiers is very small (25mA to 50mA), even a tiny power supply is sufficient to feed these amplifiers.
You can purchase power inserter from eBay or Amazon. Alternatively it can be home made. It has only two components and a housing (recycled TV Splitter). The components are (1) A capacitor to block DC from reaching Receiver DVB-T Dongle, and (2) An Inductor to act as choke to prevent RF to bypass to the power supply.