Originally Posted by keeper
I don't understand how channel 12 can interfere with Baltimore. There is a huge mountain that divides the two. When I lived in Thurmont and now in PA I never got so much as a blip in that direction of any channels. I couldn't even receive Hagerstown channels.
By "huge mountain", do you mean the northern end of the Blue Ridge? The WWPX 60 tower is located on a ridge west of Martinsburg, WV which puts the antennas at a pretty good height. I get WWPX-DT 60 on VHF 12 at 23 kW ERP at 48 miles away just fine here in Sterling, even from the backend of a Winegard YA-6713 upper VHF antenna currently aimed at DC. Post-transition, I will probably have to aim the antenna at Baltimore to get the more distant WBAL-DT and WJZ-DT (43 miles) which will put WWPX-DT off at a poor angle, but that won't matter much as WPXW-DT Ion 66 will be booming out of DC at 1000 kW on UHF 34.
The interference issue is not in Baltimore itself, but with those located at either edges of the two stations overlapping coverage zones. If the signal from one digital station is so many dB stronger than one on a adjacent channel, it can interfere with reception of the weaker signal.
The original post-transition assignment for WBAL-DT 11 called for a directional antenna at, I think, 7 kW (Trip may have the numbers). CBS owned WJZ-DT 13 opted to put up a new directional antenna which would keep the interference within acceptable limits in the direction of WWPX-DT in the west and northwest, but allowed them to put out a strong signal in other directions. WJZ-DT was able to get a 28.8 kW ERP. WBAL-DT decided to stick with their current omni-directional VHF 11 antenna and accept a lower power of 5 kW in all directions. It is going to be interesting to see how it plays out.
A delay in the analog shutdown could make it even more complicated if stations can go ahead and shut down analog if they want to. Would WUTB-TV 24 go off the air to allow WNVC-DT 56 to go live on UHF 24? Would WETA-TV 26 go dark to allow WHAG-DT 25 to go live on UHF 25? I figure the big four in each city would opt to keep their analog going.