Pastfinders Computer Users Group
September 17, 2008
High Definition Television
The history of television goes back to 1884
1884: Invention of scanning disk by Paul Gottlieb Nipkow
1922: Invention of electronic scanner by Philo Farnsworth
1936: System-A, UK: 405 lines @ 50 hz, discontinued 1986
1938: Several countries used a 441 line system, France in 1956 being the last to discontinue it
1939: System-M, USA: 525 lines @ 60 hz
1952-1956: European adoption of 625 lines @ 50 hz with PAL and SECAM color coming in 1956
1956: French (monochrome) 819 line @ 50 hz system launched, discontinued 1986
All used interlacing and a 4:3 aspect ratio.
In analogue TV, an electron beam is swept from left to right across the face of a Cathode Ray Tube and its intensity varies with the brightness of the picture desired. Once at the right edge, it quickly sweeps back to the left and starts a new line below the first. When it scans the last line it returns to the top to repeat.
The standard TV signal today is based on the 525 lines at 60 Hz. But many of the lines are used for synchronization or are lost in retrace so the actual screen presentation is 480 lines. They are arranged so that 240 lines are painted in the first 1/60th of a second and the second 240 lines are painted between each of the first in the next 1/60th of a second. This is called interlacing and it’s what the “i” represents in definitions such as 480i, 720i and 1080i.
When the complete picture can be scanned in one frame, it’s called progressive scan and the letter p is appended to the number of lines per frame. 480i is considered Standard Definition Television (SDTV). 480p is also SDTV but it is not transmitted over the air but many cable companies provide it especially for local TV weather channels.
All of the other formats are considered to be High Definition Television (HDTV). Because of the increased number of lines per frame, HDTV requires more bandwidth than SDTV unless it is converted to digital format and compressed. The compression used is called MPEG2 (Motion Picture Experts Group) and it relies on the fact that some things that the eye can’t see can be thrown away and that from frame to frame, there’s a lot of redundancy. Sort of “If it doesn’t move, don’t keep sending it”.
Because of this compression, TV stations can actually send more than one channel in the same bandwidth used by SDTV. SDTV channels are 6 MHz wide; 4.5 MHz for the picture and 1.5 MHz for the sound. In the same space, digital TV stations can transmit one HDTV program and several SDTV programs. Channel 6, for instance transmits HDTV on channel 6.1 and an SDTV weather channel on channel 6.2.
It is those subchannels that the converter will tune to for your analog set. If you are on cable or you buy a HDTV with a tuner (all are required to have one now), it will receive over the air signals and allow you to tune the sub channels. If you have an analog TV, you will need a converter box to do the tuning for you. If you are on cable, you need do nothing. However, in case your cable goes out during a hurricane or other event, you might consider getting a converter if your TV does not have a built in digital tuner.
Your converter box needs to be connected to an antenna and to the analog TV. The antenna can be simple rabbit ears but an outside antenna is better. The box can be connected to the TV using an RF cable where the TV will have to be tuned to either channel 3 or 4, whichever channel is not broadcasting in your area and the box set to the same output channel. If the TV has a Composite Video Input (Usually just marked Video In), you can connect it with a yellow video cable. You will also have to connect the two Audio Out jacks on the box to the two Audio In jacks on the TV using what is usually a cable pair with one white and one red RCA plug. There are cable sets that include the yellow, red and white connectors for the video and the audio.
Once connected, the box needs to be setup and each manufacturer will have it’s own format, but in general, you have to put batteries in the remote, turn the box and TV on, selecting either the video input on the TV or channel 3 or 4 depending on your setup, and select setup from the menu. Then you scan for channels and some boxes measure the signal strength and show you when the antenna has been optimally positioned. If all channels have their maximum signal strength with the antenna in the same position, you can leave it there. If some require the antenna to be in a different position you may have to find a setting less than optimum where you can view all channels. Otherwise, you may be required to rotate the antenna for best reception on each channel. You can remove channels from the list if you don’t ever want to watch them. Then you can choose the display format. Choose which ever one you think makes the picture look best.
Here are a few links on the subject:
https://www.dtv2009.gov/ Go here to get your coupon. You are entitled to one even if you have cable or satellite TV. You can use it in an emergency when the cable or satellite TV goes down. Or get one for your camper or summer cottage.
Google has contracts with most of the world’s major libraries to scan books so that they can be seen, read and downloaded from the Internet. Books come in four flavors; Full View, Limited Preview, Snippet Preview and No Preview Available. With Full View you can search through the book, read what you want or download the book to read and print it offline. Limited Preview allows you to search through the book but not download it and the others are more restrictive.
Go to Google.com, click on more and then on books. Or go here:
You can search in many different ways. An ancestors full name in quotes, surname of a male with his wife’s maiden name as in Davis Smith, a surname and a town, etc. Look through the resulting list for something that indicates a useful result and click on that. In the lower right you’ll find a search box that you can use to search for names throughout the book. Try your original search term first to see how many times that appears in the book. Each result gives the text surrounding your search term and shows the page that it appears on. Click on the page number to see the entire page.