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On February 17, 2009, Americans will enter the age of digital television — ready or not.
On that date, all full-power broadcast television stations will begin broadcasting only in digital, improving sound and picture quality as well as allowing for stations to offer multiple programming choices, called multicasting.
The government-mandated change will free up needed frequencies for public safety and new wireless communication offerings.
What’s the difference between analog and digital?
Since television was invented, stations have broadcast analog signals, or continuously varying radio waves. The familiar “snow” or ghosting of images is one problem with this way of sending broadcast signals. Another issue is the limited bandwidth for an ever increasing number of television channels.
After the transition, broadcasts will be sent only via digital signals, which use a series of zeroes and ones to transmit data just as a computer does. The result is clearer, more reliable picture and sound as well as the opportunity for more programming options and interactive features.
Because of how a digital signal transmits information, it has more room for additional data. So now television stations that once broadcast on one channel, such as channel 3, can now broadcast on several segments of that channel, for example: 3-1, 3-2, 3-3, 3-4. Each channel could offer specialized programming for a particular audience.
HDTV is the highest level of digital television quality, but it is not the only one. SDTV, or standard definition television format, is the quality at which basic digital broadcasts will be provided. SDTV offers an enhancement over traditional analog broadcasts, but it is not as sharp as HDTV.
What do I need to do to be ready?
If you have an analog input television and currently receive your television service through cable or satellite, you will continue to receive your current stations without needing to purchase additional equipment. However, to receive the full, original quality digital signal, you may need to upgrade your set or get special equipment from your service provider. Simply check with your cable or satellite company for more details.
Note that if your service goes out due to weather or other circumstances, you will no longer be able to receive traditional television channels without a digital tuner or digital-to-analog converter box.
If you have an analog input television and receive your signal via an outside antenna or “rabbit ears,” then you will need to purchase a digital-to-analog converter box to be able to continue watch television. Your set will continue to work as before with gaming consoles, DVD players, VCRs and other similar systems.
The new converter boxes are expected to be available in early 2008 and run between $50 and $70. From January 1, 2008 through March 31, 2009, all U.S. households are eligible for a government coupon program to offset $40 of the cost for up to two boxes per household. A list of eligible boxes is available from the National Telecommunications and Information Administration, which manages the program.
Aside from buying a converter box or signing up for a cable or satellite service, you could also choose to buy a new digital-input ready television. After May 2007, all new televisions must be ready for receiving digital signals or be clearly marked that additional equipment will be needed.
These next generation television sets are the best way to experience all that digital television has to offer.
If the store is too far away or too annoying, people shop online. I bought shoes online since I don't even know where a good shoe store is.
Find a good library that has back issues of the Bell System Technical Journal ( BSTJ ). It's all in there.
Once your analog phone voice signal reaches your local telephone exchange switching center, it is probably converted to digital for processing and forwarding to the destination exchange you are calling. There it is converted back to analog for delivery to the analog phone line you are calling.
But, for sure one day all telecom signals will be digital. (except for the RF transmittion methods)
McDonalds. Landscaping. Painting.
Radar is a fascinating subject to me as it covers practically every aspect of general engineering as well as radio communications and elecronics
I would say radio communications engineering plus electronics would be the primary subjects to start with. Digital computing methods such as Digital Signal Processing should be covered in the comms syllabus
You will need a knowledge of Microwave and millimetric techniques beyond the normal communications syllabus
You may also need a good knowledge of mechanical engineering, hydraulics engineering and low temperature physics as well if your interested in "heavy" high power ground based Radars, though aviation radar may well need these subjects as well.
A good Radar scientist/ engineer really needs to have a good working knowledge of almost every branch of engineering there is!
This is why (to me) it such an interesting field
The change for FM radio falls under the name HD Radio. Cellphones have been digital for quite sometime and have gone through several different standards. The latest deployed standards for cell phones are called CDMA2000 and UMTS. Aircraft communications would have been changed under a program called NEXCOM.
A good book on Digital Modulation is Digital Communications: Fundamentals and Applications (2nd Edition) by Sklar.
Much of the conversion from analog to digital is made possible by source coding. These methods greatly reduce the amount of data required to transmit data by techniques that might alter the actual data but appear the same. Examples in everyday life include MP3, JPEG, and MPEG.
The simplest answer is 'noise'. Since digital information moves in predetermined patterns, like ones and zeros, it is much easier to determine if a bit of 'signal' is part of the information.
Analogue can have any value signals, and so it is much more difficult to determine if there is noise (read errors) in the information.
Further, since digitalized data is quantized, it can even be counted, with totals arriving with the other information. So, as a simplified example, I can send you the word "Three" and also include that the letter count is 5, and the value count is 48 (if you use the numeric value of each letter from 1 – 26.) Now if there is a mistake in transmission, I have a way to know, and perhaps even correct the error. analogue carries no such possibilities.