This depends on what satellite your local HD Channels are broadcast. This information is not easy to find. One way is to call DIRECTV to find out where your locals are coming from.
Currently there are two main types of satellite dishes. The SL3
or SlimLine 3 Dish
receives satellite 99, 101, and 103. The SL5 or Slim Line 5 Dish
receivers all the same satellites as the SL3 (99, 101, 103) Plus satellite 110 and 119. So if you are unsure we recommend getting the SL5 Dish that covers all satellites necessary to get DIRECTV HD.