I have the HD400, but I don't yet have my HD RPTV, which is being delivered in a few weeks. I bought both of them at the same time, but took the HD400 home to become familiar with it and to make sure it was working.
The HD400 has two inputs, antenna and satellite. You can use the antenna input for either an OTA antenna or coax cable input. If you want to use both OTA and cable, you have to use a diplexer and combine the OTA antenna signal with your satellite signal. This is considered an "advanced installation technique", according to Mitsubishi.
I bought the Radio Shack double bowtie antenna just to try things out and have had it configured all three ways: OTA and sat, cable and sat, and cable and OTA/sat. With the RS antenna, I was only able to pick up one digital signal, but the HD400 worked in all three configurations. The Advanced Program Guide integrates all input signals, and through your zip code, can determine all stations correctly. I'm currently using it with a cable and satellite connection.
Widescreen Review recently gave the HD400 a favorable review.
The complete HD400 manual is available at the DirecTV web site:
http://www.directv.com/customer_cent...shi_SR-HD5.pdf
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Tom
Sony SAT-T60 Direc
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Sony SAN-24MD 24" elliptical dish