It has been discussed that the carrier
of an amplitude modulated wave does not contain any
intelligence and its power which is a considerable part
of the total power in the wave goes as waste. The question
that naturally arises is why transmit the carrier at
all. In fact, it is possible not to transmit the carrier
at all and transmit only the side-bands. This will lead
to a considerable power saving i.e. two - third of the
total power if modulation depth is 100%.
However, the suppression of the carrier wave is a transmitted
wave that leads to a considerably complicated design
at the receiving end. As a result, the receiver becomes
costlier. If the waves are used for broadcast work involving
a large number of receivers, the additional expenditures
on these receivers out-weighs the advantages of power
saving resulting from the suppressed carrier at the
transmitter. Therefore, it has become the general practice
to employ DSB - AM for broadcast service and utilize
suppressed carrier systems for radio telephone links
only.
|
| Alternately, instead of
suppressing the carrier completely it is possible to
suppress the carrier partially and transmit it at reduced
power level. But another question that immediately comes
to mind is - what is the use of sending both the side
bands when even a single side band would suffice the
needs of the communication links. In fact, it has become
the standard practice in communication circuits to transmit
only a single side band with a very low level carrier.
The carrier is generally termed as the pilot carrier
and the system is called SSB/SC. |
