By default my Air chooses 5GHz and the range is no where near as good as 2.45GHz. Take a couple of minutes and change to a clear channel on 2.45GHz and enjoy better range.
100m is quite low, I have seen the video break up at 500m on 5GHz, but 2.45GHz seems fine on mine. Try switching off Bluetooth on your phone, that has helped me in the past. Or try switching off Wifi on your phone, if it is connecting to an AP and it is so close, it will cause interference. GSM, 3G or 4G might also be causing interference with the signal, so it is worth trying it with those off as well.