Originally Posted by jtbell
Historically, transmitter facilities were erected and owned by individual stations, which later coalesced into "station groups" (Sinclair, Media General, Hearst-Argyle, etc.) that do not generally correspond to the broadcast networks (NBC, CBS, ABC etc.) In any market, these all compete against each other and usually have little or no incentive to cooperate on sharing transmitter towers. Any "national transmitter plan" would probably be denounced as "socialistic" and "anti-business" and "un-American."
Even if all broadcasters wanted to use the same tower, it's not always possible. Unless it's just a few multi-frequency antennas installed on 1 tower, then several antennas on 1 tower puts unnecessary weight on it. You also have to factor in the channel spacing & how much power specific channels can go up to without interfering with co-channels & adjacent channels. Then you also have channels in a market that are licensed to a suburb that can't be located near all the other antennas, either because it wouldn't provide Grade A coverage over the COL, or that station is short-spaced with another station. In the analog days, UHF required stations to be 6 channels apart, which prevented some stations from locating near the rest of the other stations' antennas. I know in the Chicago market, WJYS 62 Hammond, IN & WYIN 56 Gary, IN could not locate in Chicago, due to then WEHS (now WXFT) 60 Aurora, IL already broadcasting off the Sears Tower in Chicago. For WJYS, there was also WGBO 66 Joliet, IL broadcasting off the John Hancock, that prevented WJYS from locating in Chicago. For WWTO 35 Lasalle, IL, not only being short-spaced with WFLD 32 & then WCFC (now WCPX) Chicago, but also, their COL (city of license) is nearly 80 miles from Chicago, & can't provide Grade A coverage over Lasalle, IL from Chicago. That still holds true today for WWTO in the digital era, even though they're now on RF 10. That station should really be licensed to the Peoria, IL market, as it's closer to Peoria than Chicago. WJYS now broadcasts from Chicago, while money prevented WYIN from locating their antenna in Chicago, but channel spacing is no longer an issue for them, should they ever earn enough money (not likely) to locate their antenna in Chicago.