You would have to get a digital to analog converter box to recieve OTA signal on the Sligbox coax. input.
What I do, is use a HomeWorx HW-150PVR and take the componet output to the component input on the Slingbox PRO.
The advantage to using the HW-150PVR over a D/A converter is that it has a built in PVR so you can also record TV shows or timeshift live TV.
You will have to use a USB Hardrive to record shows but I use USB thumbdrives and have not had any issue.
If you wanted to use a D/A converter with it you can do that too. That way you can watch a differnt channel and record a show at the same time.
I bought my (2) HW-150PVR's on sale at NewEgg.com for $35 on sale. Regular prices is $45-$50.
Hope that helps.