Hi Alan, There are no phone masts withing 800 mtr of me so I cant see that that is the problem, as for the filter I'm not sure, the coax is the one that came with the antenna it is a single length so no joins and is about 5 mtr long. when I made the homemade spider it covered the same distance and picked up many more times aircraft than this one up to 200nm. This one only seem to pick up aircraft within about 20nm it is also about 5ft higher than the spider was. Either I have done something wrong in the set up or this areal is pants and I should go back to the homemade spider. You would of thought that the official Radarbox areal would of been the best.
Steve