Quote:
Originally Posted by be236
Well, in the analog days, I was able to pick up those 100-mile stations in VHF fine (albeit static, but watchable)... yes, I know VHF has a longer distance than UHF.. and they had high ERPs like 100-300 kWatt.
Now these new UHF stations have less than 50 kWatt, so it makes it that much harder.
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Keep in mind that analog (NTSC) signals NEEDED much more power to achieve a clear picture. They need a fairly high signal to noise ratio (say roughly a 27 dB SNR) to produce a clean (like VHS tape quality) image.
Digital (ATSC) signals can produce a clean (like DVD quality) image while using less signal power (roughly a 15 dB SNR).
The lower power of digital broadcasts does not make it harder to receive. The power was reduced to maintain roughly the same amount of coverage as the old analog systems. Since the threshold for reception has been reduced, it takes less power to get to that threshold. The high ERPs with analog stations was mostly out of necessity due to the spectral inefficiency of that signal format (developed in the 1940s and 50s).
In general, ERP is a bad way to look at station effectiveness because it does not take into account the signal type (ATSC vs. NTSC) and it does not take into account the frequency (high frequency channels require much more power than low frequency channels). For example, a 50 kW digital station on channel 7 will cover the same area as (actually even more than) a 5000 kW analog station on channel 51.