Wireless/SDR Archives

August 31, 2023 DSP / Wireless/SDR

How Automatic Gain Control (AGC) Works

Alfred North Whitehead said, "Civilization advances by extending the number of important operations which we can perform without thinking of them." In today’s world, it is easy to take no notice of the level of process automation integrated into our lives. To have an idea of how things were in the early days, signal processing technology to sort out the radar picture on a map was not available and only a dot or a line could be generated on the screen representing a detected target. A radar operator had to stare at a screen for their whole shift to raise a warning when a blip appeared on the screen, see an example below. Image credit: Plate V, J.G Crowther and

May 17, 2023 DSP / Wireless/SDR

Top 5 Software Defined Radios (SDR) for RF Experimentation

In this article, I describe 5 of the most popular SDRs available for RF experimentation today. As a 6th member of this list, I include a surprisingly common and free SDR that can be used for your fun radio projects. Table of Contents Background Where We Came From Top SDRs 5. Universal Software Radio Peripheral (USRP) 4. LimeSDR 3. HackRF One 2. ADALM-Pluto 1. RTL-SDR 0. A Free SDR We start with a little bit of background and where we came from. Background Software Defined Radio (SDR) has revolutionized wireless communication in the same way Microsoft revolutionized the scope of personal computing in its early days. Today the SDRs are used by electronics and DSP engineers, amateur radio hobbyists, physicists,

A figurative example of IQ imbalance depicting potential sources of mismatches

March 20, 2023 Wireless/SDR

Direct Conversion (Zero-IF) Receiver

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 $+F_{\text{LO}}$ and the other at the negative frequency $-F_{\text{LO}}$. A clue for the root cause of the image frequency problem appears

DDS waveform and spectrum after dithering

January 31, 2023 DSP / Wireless/SDR

Direct Digital Synthesizer (DDS)

A Direct Digital Synthesizer (DDS) is an integral part of all modern communication systems. It is a technique to produce a desired waveform, usually a sinusoid, through employing digital signal processing algorithms. As an example, in the transmitter (Tx) of a digital communication system, a Local Oscillator (LO) is required to generate a carrier sinusoid that upconverts the modulated signal to its allocated frequency in the spectrum. On the receive (Rx) side, another local oscillator downconverts this high frequency signal to baseband for further processing. Such a process is shown in the Tx and Rx block diagrams of a Quadrature Amplitude Modulation (QAM) system below. In addition to frequency translations, an oscillator with an adjustable frequency is also needed for

A discrete-time FM demodulator block diagram with atan2 and derivative filter

December 8, 2022 DSP / Wireless/SDR

Frequency Modulation (FM) and Demodulation Using DSP Techniques

Frequency Modulation (FM) is as old as the history of wireless communications itself. The past few decades saw the rise of digital signal processing in all spheres of life that pervaded even the implementation of analog modulation schemes. Today many of the FM systems are built using discrete-time techniques instead of the conventional circuitry as described below. Frequency Modulation In digital communications, data is sent through altering a characteristic of an electromagnetic wave such as amplitude, frequency or phase in discrete steps (e.g., $M$ number of levels). Such systems are known as Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK) and Phase Shift Keying (PSK), respectively. Analog modulation schemes, on the other hand, vary the desired parameter in a continuous