Hi. I have a MX-450 remote and MRF-350 base station (with the 250 external antenna). All my components are in a closet. The MX-450 remote controls all my components through RF to the MRF-350 base station. I can control every component anywhere in my house, however I can only control my Comcast Motorolla cable box from approx 20' from the closet.

Why does the MX-450/MRF-350 work from anywhere for all my components, but I am limited to 20' with the Comcast box? It doesn't make sense...

 it may be an RF interfernece issue.  when the cable box is on, it could be causing interference.

do you have the cable box programmed to turn off when doing other activities? if so, try keeping the cable box on and see if it decreases the range when using other devices.

Thanks for the response. I have the cable box on and the other components work fine (my receiver, apple tv, and DVD all work). I have the 250 external antenna mounted about 3 feet away from all components. I am using the IR extenders to each component.

All components are on and everyone works throughout my living room, dining room and kitchen, except for the cable box. The cable box only works for a section of the living room. Could it be a problem with the cable box or the IR extender?

Is the closet door closed? URC did have an issue with a batch of emitters a while back. You could try swapping emitters just to be sure there is not a problem with it. Also, have you turned up the intensity on the emitter just to be certain? Also, I'd try moving the antenna farther away and test. Sometimes, these issues are caused by what you least expect.