Chapter 3: The Receiver

3.1 Superheterodyne Receiver

The main function of the receiver is to take the smallest input signal, i.e., the minimum discernable signal (MDS) at the input of the receiver and amplify that signal to the minimum discernable signal at the A/D converter while maintaining a maximum possible S/N ratio (SNR). A typical block diagram of a receiver is shown in Figure 3-1. Most receivers are referred to as superheterodyne receivers which means that they use a common inter-mediate frequency (IF) and two stages to downconvert the signal to base-band, as shown in Figure 3-1.

Figure 3-1: Typical superheterodyne receiver.

This type of receiver is used for the following reasons:

1. A common IF can be used to reduce cost of parts and simplify design for different RF operating ranges.

2. Easy to filter image frequency since the image frequency is by two times the IF frequency.

3. Easy to filter...