Does using a aztech wireless homeplug extender affect my fibre optic connection?

my modem is on the first level and my mac and ps3 is on the 3rd level.. as i have difficulty connecting to the network downstairs, i use the homeplug extender... my connection speed is supposed to be 100mbps down and 50 up but i'm getting 10 down and 12 up.. does anyone know how to fix this or knows the cause of it?