QAM is the data format currently in use by cable television companies to transmit digital video to their subscribers. This format, which stands for quadrature amplitude modulation uses a 6 MHz bandwidth, just like ATSC uses for transmitting digital television over-the-air (OTA). It is essentially the cable equivalent of ATSC.
While QAM runs on the same bandwidth as ATSC, it carries about twice the data that can be transmitted over the air via QAM. That eliminates any direct compatibility between the two, requiring two different tuners in the receiving television to decode the two different signals. However, part of how QAM gains this great data throughput increase is by eliminating error correction. That means that QAM requires an extremely clean signal path.
This clean signal path is the holy grail of the cable television industry. All parts of their networks are designed and built with the idea of maintaining as clean a signal as possible; both on the fiber-optic and coaxial digital cable parts of their distribution system.
Most digital television signals are transmitted by cable television companies encrypted. Without encryption, they have no way of receiving income, as anyone could receive and decode their signals with standard equipment. The “black box” that one has to buy or rent from the cable television provider is a decryption device more than anything else. Without it, most of the channels broadcast over QAM are unrecognizable.
The exception to this are those television channels which are transmitted “in the clear,” hence “clear QAM.” Clean QAM exists because current FCC regulations require that the cable television companies transmit the programming of local broadcast television channels without charge.
Essentially, the FCC has maintained that any broadcast media must be made available without charge. That’s why you don’t pay your local television stations for watching the ball game or the news. This ruling extends to cable television, with the requirement mentioned above. So, all cable television companies provide this service.
However, that doesn’t mean that they are willing participants, that they have to inform their subscribers or that they have to make it easy to locate and connect to the local broadcast channels. Typically, people who have cable find that they have the local channels on their cable and people who don’t subscribe to cable never bother checking to see if they can get those channels on their television.
If a home is wired for cable, as in the case of a rental home where the previous occupant had cable television service, the cable television company doesn’t come back in to remove the cables; they are there permanently. When the previous tenant left, they took their decoder box with them, rendering the cable essentially useless, as far as most people know. But, if the new tenant were to connect their television directly to the cable, without the black box, they would be able to receive the local broadcast channels via Clear QAM.
I mentioned earlier the requirement for two different tuners in television sets so that they could decode both ATSC and Clear QAM. Since 2006, all televisions sold in the United States had both these tuners installed, with the exception of some low-end units.
Once again, although television manufacturers are required to include a QAM tuner in their products, there is no requirement to advertise that fact, make it easy to use or provide instruction on how to access it. Therefore, in many televisions, the only way that you can find those channels is to connect the cable line to the antenna input and have the television do a search for the available channels. Once they have been found, all the channels that are encoded and are unusual would have to be individually deleted from the channel selector.
The Future of Clear QAM
The future of Clear QAM is uncertain. While the FCC has argued successfully to keep Clear QAM open, as the cable companies do not “own” or pay for those signals, cable companies are fighting against that. They want to be able to charge for all services they provide, including the retransmission of local broadcast signals.
The large cable television companies have been lobbying extensively for a change in the law, in order to eliminate the requirement for Clear QAM. Were this to happen, the capability of connecting to their lines in order to receive local channels would requirement of a contract and rental of their black box.
There is a pretty good possibility that these cable companies will eventually win out, as few people are aware of the existence of Clear QAM and even fewer are suing it. They can successfully argue that the requirement to provide a free service, which is not used by the population, is a waste of time and resources.