If you are thinking of replacing a SD unit with a HD unit you will also need a new dish to receive the HD channels. If yo are just replacing a HD reciever with a HDdvr you need two lines run into the HDdvr to use all the fratures of the dvr. Your best deal might not be on e-bay but either through Directv or a local store lick costco or bestbuy. E-Bay units are not alway's what they are sold as, you could end up with one that can not be activated through Directv due to coming from a bad account. All newer HD units will be leased.