Problem with HD reception with Off Air Antenna + Directv Receiver (1 Viewer)

I apologize if this has been covered before... I searched around and couldn't find any mention of this exact problem. I have an HD Directv receiver with an Off Air Antenna input. If I connect the antenna directly to the HD TV (without going through the Directv receiver), all of my local HD channels come in crystal clear with no problems. When I connect the antenna to the Directv receiver, and connect that to the TV via HDMI, some of my local channels still look great, a couple work on and off, and one channel doesn't come through at all (the Directv receiver just says "searching for signal on off air antenna"). Has anyone else experienced anything like this? I assume it's the Directv receiver that's degrading the signal... why would the Directv receiver have such a negative impact on some of the channels? Are there any suggestions for solving this problem? I know the easy solution is to not run the antenna signal through the Directv receiver, but it would be nice to just have everything going through the receiver so that all of the channels show up in the on-screen guides and I don't have to keep switching inputs on the TV. Thanks! Brian

Assuming everything is functioning correctly, most likely the tuner section of your TV is much better/more sensitive than the tuner on your Directv box. I've had 3 HD Directv boxes over the last 3 years and the tuners vary tremendously from model to model. You don't say which model D* box you have, but the differences b/w the early generation chips and later can be tremendous. Even my 2 HR20's have significantly different (an original 700 and 1/2 year newer 100 which are made in different factories with Tuner sections from diff manufacturers).

Sorry, I should have mentioned the model of the receiver is H20-100. Your explanation makes sense... so I guess there is not much I can do other than get a different receiver!
Thanks,
Brian