The DirecTV HR21 DVR first appeared in September, and one of the key differences from the preceding HR20 was the lack of built-in ATSC tuners. While the HR20 supported satellite and ATSC, the HR21 is satellite only. This has been frustrating to many who would otherwise consider the HR21.
Well, here comes the AM21. The AM21 is a thin box that you can stack, over or under, with the HR21. It simply has two ATSC tuners and connects to the HR21 via USB. It is only $59, and once connected the functionality is just like the HR20 with integrated ATSC tuners. The ATSC channels show up on the EPG, etc.