Modulation is the process of impressing information onto a carrier signal. The choice of modulation technique directly impacts the bandwidth required for transmission. Modulation techniques like amplitude modulation (AM) and frequency modulation (FM) affect the bandwidth, with FM generally requiring a wider bandwidth compared to AM for transmitting the same amount of information. In addition, the presence of sidebands increases the bandwidth required for transmission.
Heterodyning is the process of Modulation
The process of modulating the carrier wave is called heterodyning. During the modulation process, heterodyning produces two side bands. The side bands are called the upper and lower side bands. The frequencies of sidebands would be the ‘sum of carrier and signal frequencies’ and the ‘difference between carrier and signal frequencies’. As you had guessed correctly, the upper side band would have the sum of the frequencies and the lower side band would be the difference between the frequencies. Band width of the modulated wave is the range of frequency bands occupied by a modulated wave.
Modulated Wave with Double Side Bands
We had learnt that the band width is the range of frequency bands occupied by a modulated wave. We had also learnt that Heterodyning produces two side bands called the upper and the lower side bands. Double side band (DSB) modulation keeps both the side bands intact. This means that the power of audio signal is distributed between two side bands. Therefore the power of the audio signal in each of the bands would be halved.
Modulated Wave with Single Side Bands
Since both the side bands carry the same intelligence, one of the side bands would be sufficient to carry the intelligence. In the single side band modulation, the lower side band is suppressed and all the power of audio signal is concentrated in upper side band.
Advantages of Single Side Band over Double Side Band
Single Side Band (SSB) has many advantages over the Double Side Band (DSB). Firstly, it reduces the frequency usage due to narrow bandwidth. Therefore, the remaining bandwidth could be used to accommodate more channels. SSB has lower level of interference and higher power of transmission.
Emission Designator of radio Wave
By now, you would have realised that each of the radio navigational equipment use different types of modulation, type of signal and type of information. Emission designators provide information regarding the electronic signals being transmitted and received by a particular radio aid.
Structure of Emission Designators
Emission designators consists of three parts. The first part denotes the type of modulation of the carrier wave. For example, it could be amplitude, frequency, phase or pulse modulation. The second part denotes the nature of signals modulating the carrier. The third part denotes the type of information transmitted which could be either voice or data.