It is easy to be confused by the power levels at TV stations. As you surf the web, you'll find various levels stated, these include:

• ERP - the effective radiated power including the effects of the antenna
• Transmitter Power - the transmitter alone, without the gain of the antenna
• Peak Power - the highest level of power for a given instant
• Average Power - the average value over time.

Then there's NTSC power versus DTV power and how the FCC rates them:

• NTSC stations are in Peak Power
• DTV stations are in Average Power

Next, you have to consider that the Peak-to-Average ratio for the two type of TV is different

• DTV Peak/Avg is -6.5 dB or Peak = 4.46 times Average
• NTSC Peak/Avg is -2.2 dB or Peak = 1.67 times Average (average picture)

In terms of interference (RFI), it is the peak power that is likely to have the greatest effect. The health hazard, associated with Electro-Magnetic Radiation (EMR), is a factor of average power. Using the understanding above, we can see the relationship in average and peak power between NTSC and DTV stations and their potential impact on RFI and EMR.

Although a 70KW rated DTV station looks weaker compared to a 316KW rated NTSC station, they are actually equal in terms of peak power and potential RFI. Thankfully, with the lower average power of our example, the DTV is safer.