Abstract: A feed assembly waveguide interface (10) between an antenna (12) coupled onto an upright post (14) and an outdoor radio (16), comprising a feed tube (18) connected at a first end (20) to a sub-reflector (22) and a second end (24) having a waveguide output (26). A structure (28) is for affixing the feed tube (18) internally within the antenna (12), so that the second end (24) will extend outwardly from a rear wall (30) of the antenna (12). An assembly (32) for spring loading the feed tube (18) on the affixing structure (28) will allow the second end (24) to be forced outwardly away from the rear wall (30) of the antenna (12). When the outdoor radio (16) is mounted to the rear wall (30) of the antenna (12), a positive interface connection will be made between the outdoor radio (16) and the antenna (12), thus making a solid mechanical connection between the outdoor radio (16) and the antenna (12), as well as a proper electrical and environmental seal.