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Requirements For Using Wireless Systems On TV Channels
Most wireless microphones and wireless intercoms operate on "unused" VHF or UHF TV channels. The FCC assigns channels to TV stations to maximize the number of stations that can operate in a region. Accordingly, a TV channel that is not occupied locally is very likely to be in use in another nearby city. To avoid interference with reception of TV signals from neighboring cities, the FCC has established rules to regulate use of wireless on TV channels. These are: Keep in mind that the distance requirement is from the transmitter, and not from the center of the city served by the TV station. It is not unusual for transmitters to be located 20 or 30 miles outside of a city. The requirement that wireless operation not interfere with TV reception is perhaps most important. Few things will stir the FCC into action quicker than citizen complaints about TV interference. And even though the FCC usually only requires that the wireless user immediately stop interfering, they often use such events as an opportunity to check license status. This can quickly make a little problem turn into a big one if all is not in order. There is a priority among wireless users. Local broadcasters who are licensed for the region served by the station have priority over other wireless users, even those who are properly licensed and operating legally. In case of interference, the secondary user must either select new non-interfering frequencies, or shut down. This is becoming a frequent problem at large events, where local news crews are often uninvited guests. A few venues have responded by strictly controlling wireless use on the property, many others are likely to follow. All of the more than 1,600 televisions stations in the U.S. must eventually start transmitting a DTV signal on a second TV channel. The current schedule is that all commercial stations be on-air by May 2002, and all remaining stations by May 2003. However, many broadcasters are resisting, pointing to the extremely slow sales of DTV sets. The result is that as of March 2001, fewer than 200 DTV transmitters were actually on the air. The remaining assigned DTV channels may continue to be used for wireless until the stations do begin DTV operations. Unfortunately, quite a few stations have applied for changes in their DTV or non-DTV channel assignments; several have already been approved. And after a long freeze some new stations are being approved. This is rapidly making the original DTV allocation list obsolete. In addition, determining the actual on-air schedules for new DTV channels usually requires calling the engineering manager at each station. Keep in mind that the TV station always has absolute priority, even if they change their channel of operation long after the wireless systems were installed. And in late breaking news, new proposed FCC rules (just published) call for allowing "video assist" devices to be operated in the same "unused" TV channels as for wireless mics. These devices will have 1/4- to 1/2-watt of power and will fill up an entire 6 MHz TV channel, which could otherwise support 8 or 10 wireless microphone systems. As DTV rollout expands and TV channel assignments continue to change, following the FCC rules will only get more complicated. And, regrettably, the FCC makes the necessary information available only in a scattered and fragmentary manner. Currently, the best FCC Web resources are: For the original DTV channel assignments: For current status, and pending and approved changes: For other information on the DTV rollout: Gary can be reached at stanfill@deltanet.com. |