The chip is an ITE Tech IT9135, I don't think there's a reference design freely available.
Although the result is important, getting a better signal.
But the road to it is way more important, learning.
I'm currently using the cheap and simple external antenna that came with the dongle, located outside of my window.
I'm a student living on dorms so a roof mounted antenna is out of the question.
From users experience there are still reception issues with a roof mounted antenna, this is the reason why I started thinking about designing such circuit.
After I would have a working input circuit I plan to design my own antenna, probably pcb printed.
Comparing the usb dongle to a tv tuner box, the dvb dongle got allot more signal issues, my guessing is that the compact size of the dongle adds some restrictions to the design.
I don't believe that an amplifier is a good idea, the dongle has no power issues, the cable to the antenna is quite short so the antenna signal is already amplified enough, I think that adding an amplifier would only make things worse.
I thought adding an band pass filter and amplify the output but this is already done by the chip when tuning to the frequency so I'm not sure if this is a good idea.
I think I will try to get few tuner boxes and active antennas and analyze their antenna input circuits.
Anyway I would like to get some recommendations on reading material on the subject, keep in mind this is a digital tv transmission (QAM mod').