As Alan suggests try the supplied antenna, but what part of the world/country are you in and are there other planes flying around - if they're not there, you'll not pick them up, plus not all planes are ads-b equipped (especially military), but this could be an antenna/down-lead problem -water/moisture ingress into a down-lead to antenna joint will seriously reduce signal strength, and may travel by capillary action down the lead, I've actually seen water drips coming out of a length of co-ax, where the connector joints weren't water-proofed!