Are you trying to send the satellite signal and TV signal down the same coax from the roof down into your living room? Or are you just talking about the path from your Dish receiver to your TV's antenna input?
You cannot share one coax going from the dish down to the receiver because the frequencies they use would conflict with OTA broadcast frequencies. However, if you are just talking about the RF modulated output from the receiver to your TV, then it may be possible to get things to work...
I guess the next question is, why not use a different input for the Dish receiver instead of relying on the RF modulation? If you use the HDMI or component video connectors, you'll get full HD content when available. Or you can use S-Video, or composite video for SD resolutions. Any of these "direct connect" methods will probably look better than something that has to pass through two extra RF conversion steps.
If you MUST put the Dish signal onto an RF channel, then pick a high channel number (60 is fine, do the options allow you to go higher?). Ever since the digital TV transition on June 12, 2009, all new full power OTA digital broadcasts are on channels 51 (which tops out at 698 MHz) or lower. There are still some low power repeaters/translators that exist on channels 52-69, but these upper frequencies are not used in most areas.
If your Dish receiver's output is on channel 60 (746-752 MHz), then you need a diplexor with a cutoff frequency somewhere in between your OTA channels and your Dish receiver's output (say around 722 MHz) to have them merge nicely. Diplexors at these frequencies are not commonly available, so you probably need to have one custom ordered. You might want to check out
http://www.tinlee.com/Diplexers.php?...RPOSEDIPLEXERS
For a full list of OTA frequencies, you can look here:
http://en.wikipedia.org/wiki/North_A...on_frequencies
Just remember that digital OTA stations now use channels 2-51. Use the TV Fool signal locator to find out which channels are actually occupied at your location.
Some of this information is mirrored in GroundUrMast's post. I was typing while he got his post in before me.
His suggestion of using a Jointenna can work too, but call ahead to check on availability.