You'll need an RF front end for your ADC, e.g. pre selection, mixer, IF amplifier. ADS-B bandwidth is quite low, you can receive it with a SDR (software defined radio) solution based on a DVB-T stick like this one
http://www.nooelec.com/store/sdr/sdr-receivers/nesdr-smart-sdr.html
A receiver with dual 50 MSPS ADC and FPGA signal processing allows for much higher bandwidth, but it's not particularly useful for ADS-B. There are however various SDR platforms on the net using high speed ADC and FPGA.
I already have SDR's based on dongle for ADS-B, but I want to build one based on ADS-B to learn.
About frontend, I'll use filters and LNA's based on what I already have for my dongles. More espeific, I'll use circuit like ADS-B Cape (Wide-band 1090 filter -> LNA -> Narrow-band 1090 filter -> LNA -> Logaritmic Detector/controller -> ADC):
http://ebrombaugh.studionebula.com/radio/adsb-cape/adsb_cape_schematic.pdf
What I don't understand (yet) is how do I read this high frequency (1090) since I just have an 50Mhz xtal onboard?
I know that my signal will be (almost, but not 100%) only my ADS-B data (because of filters, etc...)......but how do I read this with only 50Mhz clock on my board?
Also, I'm reading a lot of FIR filters....but I don't understand how to apply (or even if is necessary) to my project. I tried with Matlab 2015 Filter Analysis & design, but I can't build bandpass filter for 1090Mhz. Am I on correct way?
Imagining that my RF frontend is done, what's the next step?
Since I'm not electronic professional (just hobby!), I'm not sure if I understood correct logaritmic detector/controller.....but here is what I think:
in 'general way', they get input signal and generate an output 'normalized' signal.....so, if signal is too week on input, they kind of 'amplify' and generate an normalized output.....the same way if signal is too strong, the detector attenuate signal and generate the same normalized (level) output....is this right? (of course, generally speaking!)