Do you have the HDHomeRun with two F connectors?
http://en.wikipedia.org/wiki/File:Si...HDHR_Rear.jpeg
Or the single input HDHR3-US?
http://www.silicondust.com/products/models/hdhr3-us/
Are you familiar with the "HDHomeRunConfig (GUI)" aka: "C:\Program Files\Silicondust\HDHomeRun\hdhomerun_config_gui.exe" ? (on my XP box)
If so, are you seeing any indication of Signal or Symbol Quality greater than 0% when tuned to CH-21?
Here's a screen shot of it running on my 'Desktop':