TV frame

According to an PAL standard, SDTV broadcasts in three ways.
First, at ratio of length and width 16:3 and resolution 1080x500.
Second, at ratio 4:3 and resolution 704x500 
Lastly, at ratio 4:3 and resolution 480x500.
The first one has best quality, second one is next, and the last one is the worst.
There are 50 per second.
Merit.
SDTV has a similar state of resolution compared to analog TV. But SDTV is more vivid than
analog TV because it has less noise. And it has better sound. The point that SDTV uses a digital broadcasting system makes SDTV have many accompaning functions. For example, multitasking, electronic program guide, and so on. This functions are 
impossible at analog TV. Compared to AmeriTV, it has lower resolution. 
Comparison.
Generally, there are three types of TV. They are analog TV, SDTV and HDTV.