Sending analog signal over twisted pair in noisy enviroment
Should I be worried about reflections on the cable?


At 20 MHz the wavelength is 15 metres so a 1 metre cable is starting to get close to the problem area but I'd be more concerned that the LTC6363 is not going to deliver the goods at 20 MHz with a gain of 10 (20 dB). Look at the DS - it shows that it's fairly flat in gain up to about 1MHz then peaks up about 5 dB at 4 MHz then starts rolling off at about 6 MHz.

This effect will overshadow any relection nuances in my opinion.



The AD8132 that I now notice you are using (shame on you for not putting this on the schematic!) is a lot better but, still, at 20 MHz and with a gain of 20 dB there might be 2 or 3 dB attenuation and this will be of about the same order as the effect of relections.


  Would a coaxial cable be a better/simpler solution in this situation?


Use shielded twisted pairs for best signal integrity and attach the shield to ground at the receiving end.