Only HD senders

hallo i have set up TVheadend on a Raspbarry pi this works, my TV hardware is a Fritzbox 6591 Cabel and it had integratet 4 Tuners.

So my problem with VLC Player direct connect tu the Fritzbox i ca see al SD Senders, RTL, Pro7, Sat1, Kabel1, VOX, RTL2, etc
over TVheadend i have only the Senders in HD for witch i must pay: RTL HD, Pro7 HD, Sat1 HD.....
why i cant see and watch the SD Senders ond watch??