## Top 5 Software Defined Radios (SDR) for RF Experimentation

The frontend of the transceiver plays a crucial role in determining the ultimate system performance. In a previous article, we described how a superheterodyne architecture helps in enhancing the selectivity and sensitivity of the receiver. Some of the main issues with a superheterydone receiver are the image frequency and a large form factor due to multiple conversion stages. Today we discuss a direct conversion architecture, also known as zero-IF and homodyne. Recall from the concept of frequency domain that a real sinusoid at the Local Oscillator (LO) output has two impulses in its spectrum, one at a positive frequency $+F_{\text{LO}}$

## Cascaded Integrator Comb (CIC) Filters – A Staircase of DSP

In olden days, people used to have lots of kids. A famous Urdu satirist once wrote: "It has been observed that the last kid is usually the most mischievous of them all. Therefore, there should be no last kid in a family!" I remembered this line today because I have observed that starting a write-up is the most difficult task of them all. Therefore, there is no introductory paragraph in this article. Suffice it to say that this is the only topic I have found that takes you from a very small first step (just two additions) to really advanced

One of the great advantages of Digital Signal Processing (DSP) is an unexpected simplification of operations in seemingly complicated scenarios. See the Cascade Integrator Comb (CIC) filters for how to accomplish the task of sample rate conversion along with filtering with minimal resources. As another example, in wireless communications and many other applications, a frequency translation is often required in which the spectrum of a signal centered at a particular frequency needs to be moved to another frequency. From the properties of Fourier Transform, a shift by frequency $\omega_0=2\pi F_0$ requires sample-by-sample multiplication with a complex sinusoid $e^{j\omega_0 t}$. \[