Analog vs Digital Transmission
By Gary Davis
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Satellite TV. Remember the old days of analog TV, radio,
etc. Most of us do unless you’re really young. And still today
there are plenty of analog systems in use. Normal radio still
uses analog transmission. But the digital age has begun and more
and more we will use digital systems rather than analog systems.
Digital transmission systems have many advantages over analog
transmission systems, like higher quality of audio and video.
How come digital systems can transmit higher quality signals
than analog systems? The truth is that they don’t. They just use
some tricks to eliminate noise. Analog Transmission
Systems When something like video and audio, is
recorded by an analog system, the recording has a certain
quality. This recording (when done professionally) has a very
high quality. When the recording is transmitted it is modulated
directly to a carrier wave, which is then transmitted through
the air, cable, via satellite, etc. During this transmission,
the carrier and the modulated signal will loose amplitude
(power) and due to interference noise is introduced to the
carrier and its modulated signal. The result will always be a
received signal that has a lower quality than the transmitted
signal. Hence, the modulated signal, the recording, will also be
of lower quality than the original. Analog transmission
systems are unable to maintain the quality the original has.
Digital Transmission Systems In the digital
world the recording can be transmitted to another place without
loosing any quality. An exact copy of the original recording is
transmitted. So how come that digital transmission systems don’t
loose quality when transmitting a signal? Well..... Actually
they do lose quality just like the analog transmission system
does. Surprised? No Problem. Most people don’t know that
digital signals still need to be transmitted by analog
transmission systems. The trick is that a digital system doesn’t
record analog signals, but encodes analog signals into bits
(zeros and ones). A sample is taken many times per second and
the size of each sample is written down in bits. For instance a
sample with the value of 9 would be 1001 and 11 would be
1011. The digital transmission system needs to transmit
those zeros and ones, and it does this by modulating the carrier
wave. Low power for a 0 and high power for a 1 (This is the most
simple way of modulating. There are much more sophisticated
forms of modulation, but it would take a whole book to describe
them all.) So on the receiving end, it doesn’t matter
anymore what the quality of the signal is, as long as it still
is possible to identify the zeros and ones. Noise in the
received signal is no problem. A “1” with noise is still a “1”
and a “0” with noise is still a “0”. Of course the noise can not
be too high, otherwise mistakes would be made and a zero would
be received as one or a one would be received as a zero. So
Digital Transmission Systems are better because they eliminate
the effect of noise completely. You don’t look and listen to a
received signal from an original recording, but you look and
listen to a reproduced signal of the recording. The reproduction
comes from an exact copy of the original recording. The
quality of what you see and hear now depends on your TV and
Sound System. A high quality TV and Sounds System will give you
high quality Video and Audio. The negative effects of the (still
analog) transmission have been eliminated from the process.
Satellite
TV makes use of Digital Transmission Systems. What you see
at home will always be of Digital no (much less) noise
Quality.
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