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Spectrum Threats Persist

Comments made here last year are still valid. MSTV produced an educational video, which illustrated the impact unlicensed devices, operating under existing FCC Part 15 rules on broadcast TV channels, could cause to analog and digital TV reception. Supporters of the use of unlicensed devices on unused TV channels cried foul, saying that even though the FCC rules allowed out-of-channel emissions at the levels MSTV used in the video, real world equipment would be built to tougher standards. "Trust us." Given the complaints manufacturers would receive if these devices interfered with reception in the user's own home, it is doubtful that they would build such "dirty" devices as the test unit used in the MSTV video. However, under current rules, they could. As noted in a previous RF Report, one group, supporting the unlicensed devices, did call for stricter FCC rules to eliminate this problem.

Access BPL (broadband over power lines) remains a threat and some systems have caused significant interference to amateur radio operators and probably to shortwave broadcast reception as well. Most of the systems currently deployed do not use frequencies above 30 MHz and no reports to TV reception on low-band VHF or other channels have been received.

In 2005, this column carried reports on threats to the 2 GHz broadcast auxiliary band, including Department of Defense uplinks and an attempt by Clarity Broadcasting to use the 2 GHz broadcast auxiliary spectrum to deliver multi-channel TV programming to truckers and RVs at truck stops. One problem with "Trucker TV" is that not only could it interfere with ENG receive sites near to, or within line-of-site of these truck stops, any ENG operations at these sites that disrupt "Trucker TV" reception could put ENG crews in an uncomfortable situation. The last report in this column on "Trucker TV" testing raised some questions about the test procedures and whether they were really representative of how the final system would perform.

Last year this column predicted that the big interference story in 2005 wouldn't be BPL or unlicensed devices, but rather interference between TV stations, as stations increase DTV power to meet the July 2005 and July 2006 deadlines. So far, the number of reports of new DTV interference hasn't increased. Newer DTV receivers, like the Samsung unit featured in the Dec. 7, 2005 RF Technology column, offer much better adjacent channel rejection than older designs, which will help DTV to DTV interference. However, it would have been expected by now that more UHF TV stations would be reporting degradation of analog TV reception by a high power adjacent channel DTV stations.