Modulation

In order to convey speech on the RF, either in analog or digital form, the transmitted information must be propagated on the radio link. It must be placed on the carrier. A carrier in this respect is a single radio frequency. The process of combining the audio and the radio signals is known as modulation. The resultant waveform is known as a modulated waveform. Modulation is a form of change process where we change the input information into a suitable format for the transmission medium. We also changed the information by demodulating the signal at the receiving end.

Three normal forms of modulation are used:

Amplitude Shift Keying (ASK)

In ASK (see Figure 21-24), the radio wave is modulated by shifting on the amplitude. The frequency is left constant, but the amplitude is shifted high if the data is a 0 and low if the data is a 1. Normally, we see two amplitude shifts represent a single bit.

Input Data 0 0

Normal (Unmodulated Carrier)

Modulated Carrier

WVIHV^

Figure 21-24: ASK

Frequency Shift Keying (FSK)

The alternative to ASK is FSK. In the case of FSK (see Figure 21-25), applying the data onto the radio wave modulates the carrier by changing the frequency. The amplitude is kept constant, and the frequency is changed. Normally, a single frequency shift represents a bit of data.

Input Data 0 0

Normal (Unmodulated Carrier)

Was this article helpful?

0 0
Mobile Apps Made Easy

Mobile Apps Made Easy

Quick start guide to skyrocket your offline and online business success with mobile apps. If you know anything about mobile devices, you’ve probably heard that famous phrase coined by one of the mobile device’s most prolific creators proclaiming that there’s an app for pretty much everything.

Get My Free Training Guide


Post a comment