The Rise of Digital Television Broadcasting
From my point of view as a Television Broadcast Engineer
Digital communications techniques had been is use for quite a long time before anyone thought to apply that technology to Television broadcasting. The reasons for doing so are many, and some of them will be outlined in this article. Television Broadcasting in the United States had stayed essentially the same since the adoption of the electronic form of Television broadcasting that we all knew as analog Television. Analog Television served us well in its 50 plus years of use, but as with many types of technology, it was destined to be improved upon by the digital information age, and that revolutionary change is now upon us.
The promise of the digital Television transition held many unknowns for Broadcasters and viewers alike until the development was well under way. The United States was not the first country to transition, but we are one of the earlier adopters. Even today, some of the worlds most prominent nations are still well behind the U.S. in regards to converting to digital Television Broadcasting.
Unfortunately, one of the early promises of digital Television broadcasting was never kept, and that was the possibility of adopting a single world wide digital Television broadcasting standard, which did not develop due to many reasons, with some being technical, but with most being political. In the past with analog Television, there were 3 major Television broadcasting methods used world wide, ( NTSC, PAL and SECAM) and none of them were compatible with the other. Engineers had hoped for adopting the single standard previously mentioned, but that never became a reality.
One of the initial arguments for converting to digital has always baffled me, and that is the fact that analog broadcasting was considered inefficient in its use of a 6 MHz. wide broadcast channel, but that is still the size of the DTV broadcast channel today. Now I do see the logic that a broadcaster could now send out multiple programs, but the channel size remains the same as the old analog channel, so in reality, we did not have a net gain of bandwidth recovery that was realized, but we did gain the multiple programs advantage. One more realized gain was the ability to group adjacent broadcast channels or transmitters in the same area without interference from those adjacent channels or transmitters. Adjacent channel use in analog was normally avoided due to interference issues to those adjacent analog channels themselves.
One big advantage of the transition to most broadcasters, and to the UHF broadcasters especially is the energy efficiency factor of modern DTV transmitters, which is much greater than its analog cousin. The old UHF transmitters high power amplifier tubes ( Klystron Amplifier Tubes were used in most cases ) were not very energy efficient as opposed to a modern DTV transmitters amplifier design.
In addition, a minimum of two of these energy inefficient tubes, and in some cases three or more were needed to broadcast high power UHF analog Television signals. The picture was sent in Amplitude Modulation (AM) mode, and the sound was broadcast in the Frequency Modulation (FM) mode, and the signals were then combined together into the 6 MHz. channel previously mentioned, before being sent to the broadcast antenna for transmission.
Most full power broadcasters can now be considered as “Green Energy Users’ simply due to the energy savings provided by the new Television broadcasting method, and I have seen no one else mention this fact at all. My employers power bill went from $11,000 per month per transmitter to just over $6,000 per month. That is a major benefit to broadcasters, as well as the power production industry that no one in or out of the industry has made light of. The power company that serves ours and other co-located transmitters was shocked by the drop in the power demand from the transition to digital broadcasting, and power related issues have almost disappeared due to the lower demand on the power infrastructure at the transmitter sites.
The digital broadcast transition was poorly managed, and poorly promoted.
The promotion of the transition to digital broadcasting was very misleading to the public, and created major headaches for viewers, broadcasters, and especially the taxpayer. The converter box program administered by the government, and paid for by the taxpayer was grossly mishandled, and the result was a flood of unreliable products that were rushed into production by companies who had never produced a Television related product in the past.
Not all converter boxes suffered this fate, but a large number of them did due to the governments limit of a $40 suggested retail price per box. This low price limit led many manufacturers to provide lower quality products that have a higher than normal failure rate, and only provided a basic signal output equal to the current analog signal of the time. This was also mandated by the governments regulations on converter box specifications. This of course does not include the products of some of the better known electronics manufactures such as Zenith / LG and others who actually produced a quality product for the given price range.
The media promotion of the digital transition was handled by the National Telecommunications and Information Administration (NTIA), and the Consumer Electronics Association (CEA), and is considered by many as a dismal failure. It was also handled very poorly, and was very confusing and misleading to the consumer, and they did very little justice to the concept of digital Television broadcasting by their poor promotion of a very good product, which is broadcast digital Television. The promotion of “Magic Rabbit Ears” in the thousands of promotional adds we all saw during the transition period was deceptive and misleading.
Just because a radio or Television signal carries digital data, does not make it magic and suddenly allow reception on a pair of rabbit ears. These signals still have to obey the basic rules of physics that govern the behavior of all radio signals. If you needed an outdoor antenna with analog Television , you would also need one for digital Television, in almost 99.9% of the cases. The images we all saw of the “Magic Rabbit Ears”, led the average non technical viewer to believe that the new digital Television signals could suddenly now be received using a set of those “Magic Rabbit Ears”. Talk about misleading the public on a topic, and the NTIA and the CEA are guilty, as is typical of most government administered programs of this type.
All of the testing done by the FCC and the engineers during the development of the DTV transmission method was done using antennas elevated at 30 feet or higher, as has always been the height suggested by the FCC for best possible Television reception, and since the basic rules of physics still apply to digital Television signals, the FCC used the existing standards to test DTV reception principals also. So why did the NTIA and the CEA promote the “Magic Rabbit Ears” when the FCC had other specifications already in place, and was currently testing with those standards? Only they know for sure, but there has been much speculation as to why this was.
Broadcast Television signals have much better video quality than other transmission methods
Digital broadcasting has revolutionized Television broadcasting to an extent only dreamed of in the past. The video quality of a broadcast High Definition signal is far superior to most all other transmission methods. The broadcast HD signal has much better video resolution than those same HD signals when viewed using other popular transmission methods such as satellite or cable Television. Those two transmission methods normally “Steal” video resolution from each signal they carry, thus degrading the video quality to a certain extent. The amount of degradation is solely determined by the systems engineers, and is done to save “bandwidth”on their individual transport systems.
Bandwidth can be compared to a pipe carrying water, and that pipe is only so big, and can carry only so much water. If this pipe has to supply water to only 10 users, then is is easily capable of doing so. If the demand suddenly increases to 20 users, but the pipe size stays the same, then each of the users have to be delivered a little less water due to the pipe size. This example is comparable to how the other transmission methods “Steal” video resolution from each signal they carry on their systems to be able to fit all of those signals into their bandwidth or “Pipe”.
The overall quality of broadcast Television now rivals every aspect of satellite or cable delivered signals. Those methods had an advantage over analog Television signals in the past such as the capability to provide features such as program ratings, a description of the currently airing show, a real time clock and a program guide for the broadcasters entire line up of shows well into the broadcast schedule, and in some cases well into the next broadcast days schedule.
What most people have not realized is that the DTV broadcast data transport stream is much more than a broadcast method for Television signals. It has other uses as a one way data transport system whose future uses have not even been thought of as of now. There used to be a terrestrial broadcast system known as MUZAK (also known as elevator music) that utilized the sub-carriers of broadcast FM radio signals. That system has basically converted to all satellite transmission now, but similar services can now be carried on broadcast Television data streams, as voice or music data demands are very small compared to video services, and not all Television broadcasters are currently using all of the available space in their “pipe”. This option was not available to Television broadcasters using the old analog broadcast method.
Digital Television reception issues explained.
The reception of digital Television signals has several minor issues that are now being addressed by the broadcast industry. The first issue that effects digital Television signals is a phenomenon known as multi-path signals, which are more commonly referred to as ghost signals. The effects of ghost signals in analog broadcasting were shadows, or multiple images on the screen. Ghost signals are basically just signals that take a longer path to your antenna than the main signal by reflecting off of a distant object, and arriving at your antenna slightly lagging in time when compared to the direct path signal.
This timing difference between the direct path and the ghost signals is the main cause of the reception problems that some viewers are experiencing, as it actually causes digital Television receivers to become confused since they cannot determine which is the main or direct path signal, so viewers see the dreaded “No Signal” logo on their screens. The “No Signal” indicator is actually misleading to viewers, as it is not always a “No Signal” issue that is causing the problem, but is actually a ghost signal that causes most of the reception problems that some viewers are seeing. There are answers to the reception issues, and that is where this forum comes into play, and the users, moderators and contributors are very knowledgeable and helpful on this topic, and can normally resolve reception issues in most cases with great results.
There are currently some very real and worrisome threats to the concept of DTV broadcasting, and that involves of the basic laws of the physics of the radio spectrum itself. The broadband industry (Cell Phones, I phones, Smart phones etc.) are using excessive amounts of the precious radio spectrum, and making room for them in the radio spectrum was one of the main reasons for the digital Television transition, along with making room for additional public safety services.
The public safety services plan was a big failure, as almost none of the recovered spectrum has ever been used for that purpose in most areas of the country, as was the converter box program, which is typical of most big government directed programs of this nature. The needs of Cell Phone users are no more important than those of Television viewers, as the Television broadcasting infrastructure has been around for much longer than the broadband infrastructure, and it is better prepared to handle emergency communications to the masses than the relatively new broadband infrastructure will ever be.
Television broadcasters have always had the “Broadcasting in the Public Interest” requirements placed upon them by the government for public service and emergency communications needs. This has always been the major reason that Television broadcasters have had exclusive use of a certain set of frequencies or channels they have always used in the past.
Television broadcasters have invested heavily into the “Public Service” aspect of their operations in regards to emergency communications by maintaining alternate power sources for their broadcast infrastructure. This basically involves back up power sources such as large generators that are used to power their broadcast infrastructure during times of extended power outages such as Hurricane Katrina, or in times of Cell Phone infrastructure overload that was experienced during the 9-11-2001 World Trade Center disaster. These two events have proven beyond a doubt that the broadband infrastructure is not as reliable as the Television broadcast infrastructure has proven to be.
The broadband system has no such “Public interest”requirements, and their motive is purely for profit, and they will never achieve the reliability factor that the Television broadcasters currently employ, simply because they have no “Public interest” requirements placed upon them by the government, and most likely never will. At last count, there were many more Television users than I phone users, and just because a new “Fad” is currently popular, does that give it precedence over the tried and true emergency communications system? To many people inside and outside of the Television broadcast industry, that answer is a big fat NO!!
The lobbying power of the broadband industry is great, and is a very big threat to broadcast Television as we currently know it, and it will take a very loud response from the broadcasters and the public alike to save this powerful broadcast medium who’s potential uses have not been fully discovered or utilized, and to me, it would be almost criminal to relegate it to Dinosaur status even before the ink is dry on the DTV transition.
If you think emergency communications should be just as important as the fad like needs of Cell Phone users, then you need to join the ongoing fight to save this new and exciting technology before the “Greed Factor” takes over all aspects of our current emergency communications system that has a proven track record in direct contrast to the lack of emergency preparedness that the broadband infrastructure obviously suffers from.
Opinions by a current Amateur Radio Operator, a former 2-way radio technician, and a current UHF Television broadcast Engineer.