I have been seeing ads on the TV stating that there's some kind of movement which supposedly threatens to end over-the-air TV broadcasts to the public -- which doesn't make much sense after all the hassle of changing over to Digital broadcasts. What are they talking about? It doesn't elaborate on it, and what is even more strange, it doesn't even have a website to visit for more info.
OTOH, over the air digital is [typically | often | always] (I don't have good citations) of better quality than cable or satellite, as it may not be as heavily compressed. This could argue for *more* interest in OTA HDTV broadcasts.
OTOH, if it's digital then it can be encrypted, so it may be OTA but potentially no longer free.
OTOH, revenue is revenue and a relatively small proportion of the population is OTA only (raises hand). Dumping it altogether and auctioning the spectrum could be a quick cash infusion for the Treasury.
One other item I've seen written about that is being considered is to do away with the One Big Antenna system and to seed the service area with multiple, low-power transmitters on the cell infrastructure. The reasoning seems to be that the ghost rejection in existing DTV receivers is already pretty good and could be improved in step with the antenna transitions. The result may be cheaper for the broadcaster and could potentially allow more OTA channels in a given region.
Is it really possible to use on-channel gap fillers and even build a single frequency network (SFN) using 8VSB DTV ?
I was under the impression that only COFDM DVB-T could properly support SFN.
In Finland two new VHF multiplexes for HDTV are currently bering built using COFDM DVB-T2 by a cellular phone company, using their existing medium to small (less than 100 m) masts instead of large 300 m masts traditionally used for broadcasting.
The exact same signal is radiated at the same frequency from all transmitters in the area, so in practice, a receiver could get a few thousand subcarriers from one transmitter and the rest from the other transmitter, if there is deep nulls due to multipath on some subcarriers from the first transmitter.
A bunch of the high tech outfits want to use the TV bands for part 15 liscense free wi-fi stuff. This proposed equipment is supposed to be smart enough to not jam an active channel, but that's wishful engineering.
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Maybe, maybe not - Say channel 6 (just pulling one out of thin air for use as an example), is "empty" in "Town A". That doesn't mean channel 6 isn't being used - It could very well be that it's been deliberately left "empty" there because in "Town B", there's a station transmitting on it, and if someone were to fire up a transmitter in "Town A" on channel 6, it would step on (or be stepped on by) the transmitter in "Town B".
In which case, letting Joe-whoever transmit Wi-Fi on it would very likely cause unacceptable interference to reception in "Town A", and depending on the power levels involved, could potentially cause trouble in "Town B" as well.
Also, keep in mind that *THE BROADCASTERS* have *VERY* little control over which channels they're able to use - Sure, everybody and his dog could say "I'm using this channel", but there's this entity here in the USA called the FCC, and they've pretty much been made the "dictator for life" in almost all aspects of what happens where on the radio spectrum. You want to start broadcasting? You ask the FCC for permission, and in most cases, they tell you which channel you can use, regardless of what channel you might want. You don't play by their rules, they fine you multiple thousands of dollars per day until you can't afford to make the mortgage payments and have to shut down for lack of a place to broadcast from, and/or they come pull your plug for you.
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If the intention is to serve Town A with Program A and nearby Town B with Program B on the same channel, then the old tradition to use a single 300 m tower in each town will fail.
According to claims in this threads that even current ATSC 8VSB receivers would be capable of operating with some kind of single frequency network (SFN), using lo to medium power transmitters on medium height poles within the town, will help to concentrate the signal to the intended reception area and keeping the spill over to adjacent cells at acceptable level.
This is known as the "hidden transmitter problem" as in any CSMA network, in which a device in an unfavorable location can not hear that there is some other activity on the channel. Thus the device will fire up the transmitter thinking that the channel is free.
I don't think that those devices are going to cause problems in locations, in which the TV signal is strong enough for indoor antennas, since also the device most likely will hear some activity on the channel, even if the signal level would be insufficient for TV reception at that spot.
The situation gets complicated when the TV signal strength is so low that directional outdoor antennas must be used. A device in the basement would get no TV signal at all and thinking that the channel is free, fire up the transmitter and cause interference to TV reception.
A SFN style TV network would help to keep the TV signal level at sufficient levels even indoors, preventing the device from transmitting on that channel.
Practically every country has such organizations for frequency coordination. However, at least in US the broadcasters have had a very strong lobby groups influencing the FCC.
Frequency bands are allocated for various services such as broadcasting by international agreement within ITU-R (ex CCIR) and the allocation is more or less the same at least within a continent.
In the US, the demands for setting up your own TV station is so high that available spectrum would not be sufficient and the FCC tries to arbitrate between the various players in the broadcast industry. You enemy is not the FCC but the next door TV station, competing for frequencies and for income from advertisement.
The relative importance of broadcasting has been reduced with much new technology used by the majority of people, so for instance cellular phone lobby groups have much more influence on FCC and similar organizations worldwide.
The cellular and Wi-Fi industry has traditionally had only very narrow frequency bands (compared to broadcasting) and hence frequency efficiency has been very important from the start.
However, in broadcast industry, the frequency efficiency has been quite bad and the only improvement in frequency efficiency since the
1930's was the digitalization, allowing 4-6 times the number of channels compared to the analog era. On the network level, the spectral efficiency is still poor compared to the cellular phone industry.
Sigh. Read up on 'The 150 mile rule'. TV frequencies are subject to skip, ghosting, signal fade and a lot of other problems. Also there are grade 'A' and grade 'B' coverage areas. I got a letter at a TV station who's transmitter is near Daytona Beach back in the '80s from a man in west Texas reporting that he had a clear signal for a few minutes short of eight hours one evening.
You still seem to be living in the analog era with big transmitter towers :-).
I am fully aware of tropospheric ducting an other tropospheric propagation modes.
The only surprising thing is that the transmitter was on the East cost of Florida. Typically this kind of ducting occurs only a few meters above water. Radio amateurs have made contacts up to 1000 km up to 10 GHz with antennas just a few meters above the water front, while antennas a few meters higher were useless.
Perhaps the transmitted signal had reached an elevation just few meters above the sea level, when it reached the West cost of Florida, before being ducted into Texas.
Some broadcasting companies have done quite a lot measurements for decades to detect such propagation anomalies and the potential for interference to their services. Practical experience also show that the interference could be so bad that the intended audience is not reached.
One might expect that similar propagation anomalies would cause havoc to cellular phone networks (similar to trying to use a cellular phone in an aeroplane), but I have never heard of problems due to tropospheric propagation. Apparently the lower tower heights and the higher signal levels at the intended service area, will handle most of these problems.
I can confirm that. I've got confirmed qls of 2000 miles on VHF and
1200 miles on UHF. Winding the tower up caused the signals to get weaker and disappear. Another local ham 60ft higher than me broke in to ask who I was talking to, because he couldn't hear the other side.
Dutch VHF television used to be an everyday occurrence here the UK.
The first problem I have with all of this that US telcos are a national embarrassment. They state that the FCC has no right to control their Internet services as a public utility yet any competition with them unleashes lawsuits for unlawful competition with a public utility. Until the FCC grows a pair, I'd rather have TV over the air than through the telcos.
The second problem I have with this is Google. Google doesn't really give a crap about wireless broadband. Google wants whitespace WiFi because they're going to solve interference problems using a large geolocation database that can pinpoint exactly where ever Internet customer is. I know it sounds too crazy to be true, but search for "google geolocation service" and you'll see that it's already online.
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