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Digital TV equals big electric bills

Mon, 09/30/1996 - 8:00pm
Jeffrey Krauss, Electric Bill Payer and President of Telecommunications and Technology Policy
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By Jeffrey Krauss, electric bill payer and President of Telecommunications and Technology Policy

It shows that some broadcasters will be hit with big electric bills, because they have to use UHF channels for DTV, rather than their current VHF channels. In addition, I've noted some new interference problems that could arise, one of which could affect cable TV.

The new assignment table

The FCC plans to give each existing TV broadcaster a second TV channel to use for DTV. After about 10 years, the broadcasters will give back their current analog TV channel. The Grand Alliance DTV signal is much more robust than the analog NTSC TV signal. This makes it possible to assign TV channels for DTV that cannot be used for NTSC transmissions because of interference. In fact, the Grand Alliance design is so good that nearly all the new DTV channels can be assigned to TV channels 7 to 51, so that channels 2 to 6 and 52 to 69 can eventually be used for some other service.

However, channels 2 to 6 have the advantage that they are lower in frequency, and the laws of physics guarantee that it takes less power to make a lower frequency signal travel a certain distance than a higher frequency signal. So some stations are going to encounter huge increases in electric bills when they go on the air with DTV on a UHF channel.

TV channelMaximum ERP (kilowatts)Output power (kilowatts)Monthly cost of electricity ($)
2–61005360
7–13316151,080
14–695,00025018,000

Power

The table above shows the maximum Effective Radiated Power (ERP) allowed for TV broadcasting, the corresponding output power and the monthly cost of electricity. The ERP includes both the output power of the transmitter and the gain of the antenna, which I have assumed to be 13 dB, or a factor of 20, in calculating the corresponding output power. The electricity cost is based on a rate of 10 cents per kilowatt hour.

The new FCC assignment table calculates the power that each new DTV station needs to roughly replicate the coverage area of its existing NTSC station. Most stations won't need the maximum power to reach their existing viewers, but many will need big increases.

Here are some examples. Channels 2 and 5 in Atlanta now have 100 kW ERP levels; the FCC table shows them being assigned to use channels 51 and 50 for DTV, with ERP levels of nearly 4,000 kW. Channels 2, 4 and 6 in Miami would be assigned to channels 47, 48 and 41, with ERP levels also around 4,000 kW. In Washington, D.C., two VHF stations (4 and 5) would be assigned to use 36 and 30, with ERP levels of the maximum 5,000 kW, and the other two VHF stations (7 and 9) would be assigned to use 33 and 59, with ERP levels of 3,000 kW. (The difference between these two power levels is because the channel 4 and 5 signals today cover 6.6 million viewers, while channels 7 and 9 cover only 6.4 million.)

I've also noticed a few instances where the FCC table creates competitive disparities between TV stations in a market. For example, channel 3 in Las Vegas would get to use channel 49, requiring an ERP level of 5,000 kW, while channels 8 and 10 would get to use channels 7 and 11, with ERP levels of 10 kW; all three stations would cover roughly the same population of viewers. Broadcasters will be looking closely at this aspect of the new assignment table, and undoubtedly, there will be some fights.

Interference

The FCC program that generated the table is supposed to give special treatment to channels 3 and 4, avoiding a new assignment on one if the other is already in use in a city. This is done to minimize interference to cable boxes and VCRs, which use channel 3 or 4 as the output channel to the TV set. But this special treatment evidently wasn't possible in Cleveland, where channel 3 is already in use, and the table assigns channel 4 for DTV use. The cable industry needs to analyze what interference risk the new channel 4 DTV transmissions might create for cable boxes that now use channel 4 for the output signal. Maybe special cable boxes (and VCRs) that use channel 2 for output will have to be designed for Cleveland.

The FCC program is also supposed to give special treatment to channel 69, the TV channel with the highest frequency (800–806 MHz) and directly adjacent in frequency to land mobile operations. When a TV station went on the air on channel 69 in Atlanta a few years ago, it created huge interference problems for land mobile systems.

After years of legal battles and equipment tests, the FCC eventually ordered the TV station to reduce power and install special filters. Unfortunately, the table assigns channel 69 for DTV use in Washington D.C., Chicago and a few other cities.

As broadcasters and others start to analyze the new FCC table, I'm sure they'll find additional problems to complain about. The transition to digital television will be painful, and more painful for some than for others. The burden is now on those broadcasters to come up with an improved assignment plan.

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