unclehonkey said:
As an outsider, all I can see is that highly visible engineering people must have been sleeping through much of their elementary school mathematics classes, and missed the parts on multiplication and division. Let's see if the rest of you can pass this test: If a UHF TV station was allowed to transmit 5 million watts video power in analog, and then given permission to use 1 million watts for digital, that would mean that the digital signal is using 20% of the power of previous analog signal.
Problem is, analog watts & digital watts are different.
(yes, that statement deserves an explanation
)
TV, both analog and digital, uses amplitude modulation. That means the transmitted power is continuously changing. You might say WJZ-TV is running 316,000 watts of analog power, but in practice most of the time, WJZ-TV's analog power is different. Similarly, you might say WJZ-TV is running 33,800 watts of digital power, but in practice most of the time WJZ-TV's digital power is different.
In analog, you could predict when the next power peak was going to come along. The synchronizing pulses were transmitted with the maximum available power, and they were transmitted at a well-regulated interval. Analog power was measured during these peaks. So if you say WJZ-TV is running 316,000 watts of analog power, you mean that 316,000 watts is the most power WJZ-TV will ever transmit. Most of the time, the transmitted power is quite a bit less. (the brighter the picture, the less power)
In digital, you still have peaks of power -- but you can't predict when they are going to happen. So digital power is *average* power -- the transmitted power averaged over some amount of time. (a few seconds IIRC) When you say WJZ-TV is running 33,800 watts of digital power, in fact their power is less than that half of the time -- but it's also *more* than 33,800 watts about half the time.
The conversion factor is in the ballpark of 2:1. WJZ-TV's analog power, measured using the digital method (averaged over time), was roughly 150,000 watts; WJZ-TV's digital power, measured using the analog method (at power peaks) is roughly 70,000 watts.
Now, there is still a difference - we're comparing 150,000 average analog watts vs. 34,000 average digital watts, or 316,000 peak analog watts vs. 70,000 peak digital watts. But the difference isn't as dramatic as it may appear.
IMHO a significant problem is that of poor antennas. The economic downturn coincided with the digital conversion; we've seen quite a few viewers switch from cable/satellite to OTA reception. These are folks who haven't had a TV antenna for years. They go out to buy an antenna so they can stop paying cable bills -- and what do they find at Radio Shack/Wal-Mart/Target/Best Buy? Well, whatever they find, it isn't designed to work at VHF. Not even if the box says it is. (the FCC tested a bunch of antennas last year. They found all of them were FAR inferior at VHF compared to UHF. They didn't even bother testing them on low-VHF.)
I wouldn't be too surprised if 2nd-harmonic interference from FM stations is also part of the problem. In many markets, stations are using high-VHF channels that weren't used in the analog era.
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Yes, WTVF moved from RF-5 to RF-25 over the weekend. They have already relicensed RF-5 as a Digital Replacement Translator, at reduced power of 3kw. (it was operating at 22kw when it was their main transmitter) They have requested a waiver to allow them to operate RF-5 at the full 22kw. The request states that they need RF-5 to reach rural audiences that RF-25 won't reach. (I have heard from rural viewers who say WTVF is the only station they can get, including one who was watching in Cookeville with indoor rabbit ears. Cookeville is 75 miles away!)
Of course, our Cookeville example notwithstanding, rural viewers have always needed a "real" outdoor antenna. Analog didn't work without it, and digital doesn't either. The move to 25 is, IMHO, WTVF's recognition that urban viewers near the station are either unwilling or unable to install a proper antenna.
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To jump back on-topic
:
For technical changes to existing stations, there's a "D/U" thing. Interference is assumed to exist if the new facilities are less than 28dB weaker than those of an existing station on the lower adjacent channel. (26dB if the existing station is on the *upper* adjacent channel) As I read it, you cannot cause interference to more than 2% of the homes in the existing station's coverage area that don't already receive interference; and you cannot cause any interference if it would result in more than 10% of the existing station's audience receiving interference.
The "donut hole" thing is for new DTV channel allotments.
- For a VHF channel in Zone I (the Northeast): A new allotment must be at least 110km from an existing station on the adjacent channel, *OR* within 20km of that station.
- For a VHF channel elsewhere: A new allotment must be at least 110km from an existing station on the adjacent channel, *OR* within 23km of that station.
- For a UHF channel anywhere: A new allotment must be at least 110km from an existing station on the adjacent channel, *OR* within 24km of that station.
The FCC isn't accepting petitions for new DTV channel allotments, and with the incentive auctions & channel refarming, I think it's very likely they never will. So these figures are probably purely academic.
Please contact an allocations engineer before you risk any money on the basis of anything above!
