So, by suppressing one sideband along with the carrier, no any information is lost. Hence, the bandwidth requirement also gets reduced to half and there are chances for an accommodation of twice number of channels using the SSB modulation technique. It is a combination of 2 sidebands,. But, due to the presence of single sideband in SSB modulation, the bandwidth requirement is reduced to half.
As the DSB output contains the two sidebands, and only carrier component is suppressed, so sideband suppression filter is needed further in order to eliminate one of the 2 sidebands.
The filter characteristics should be such that, it must have flat passband and should possess high attenuation beyond the passband. So, to have such a response, the tuned circuit must have a very high Q factor.
To have such a high Q factor it is needed that the difference between modulating frequency and carrier frequency to be high. This high-frequency component can then be filtered out, leaving the original audio-frequency signal.
The largest excursion the largest magnitude of that envelope is called the peak of the envelope. This factor is important because the power measurement for an SSB signal is often defined by its peak envelope power. Discussions of RF power often concern the RMS voltages which can be computed by looking at the peak voltage divided by square root of two. It is illuminating to review a few RF AM envelopes.
With ordinary AM without any audio input, the envelope of the AM carrier is not zero. It is half of the maximum peak-to-peak voltage. For example, a W AM transmitter the ideal carrier amplitude would be 25 W. In contrast, the SSB has no output when there is no audio input and, thus, no envelope. If a single tone is applied to an AM transmitter the result is an RF envelope where the upper and lower envelopes are essentially inverses of each other that follow the amplitude of the baseband or audio signal.
In the case of SSB, a single audio frequency will result in a constant-amplitude, constant-frequency RF envelope. Consequently, application of a single tone to an SSB transmitter provides a way to measure peak envelope power directly with an RF power meter.
However, sometimes commercial SSB transmitters are not rated to put put out full peak envelope power continuously as would happen in the transmission of a single tone. The peak envelope level for power can be calculated in Watts. These are just the power stages related to 1 Watt otherwise 1 mW.
The advantages of single-sideband modulation mainly include the following. The disadvantages of single-sideband modulation mainly include the following.
It is often necessary to define the output power of a single sideband transmitter or single sideband transmission. For example it is necessary to know the power of a transmitter used for two way radio communication to enable its effectiveness to be judged for particular applications. Power measurement for an SSB signal is not as easy as it is for many other types of transmission because the actual output power is dependent upon the level of the modulating signal.
To overcome this a measure known as the peak envelope power PEP is used. This takes the power of the RF envelope of the transmission and uses the peak level of the signal at any instant and it includes any components that may be present. Obviously this includes the sideband being used, but it also includes any residual carrier that may be transmitted.
The level of the peak envelope power may be stated in Watts, or nowadays figures quoted in dBW or dBm may be used. These are simply the power levels relative to 1 Watt or 1 milliwatt respectively. As an example a signal of 10 watts peak envelope power is 10 dB above a 1 Watt signal and therefore it has a power of 10 dBW.
Similar logic can be used to determine powers in dBm. There are many variants of single sideband modulation that are used, and there are several different abbreviations for them. These are explained below. This form of single sideband modulation is formed when the lower sideband only of the original signal is transmitted. Typically this is used by radio amateurs or radio hams on their allocations below 9 MHz. This form of single sideband modulation is formed when the upper sideband only of the original signal is transmitted.
Typically this form of SSB modulation is used by professional users on all frequencies and by radio amateurs or radio hams on their allocations above 9 MHz. DSB: This is Double Sideband and it is a form of modulation where an AM signal is taken and the carrier is removed to leave the two sidebands.
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