From Bits to Waves – Building a Modern Digital Radio

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Welcome to Bits2Waves, a 1-day experience on building your own modern, digital radio. You will learn how modern radios work, from communication theory to fabricating microwave PCBS to measurements with our mini-VNA.  At the end you will complete a 950 MHz QAM radio.

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In this fun and interactive experience participants will learn the basic theory of modern digital radios as well as the RF circuits and system used to build them. After an introductory session on digital radios, participants will select an RF building block to design and build. There will be short mini-classes (run in parallel) on each component: double balanced mixer, microstrip filters, low noise amplifiers, power amplifiers, baluns, etc. The radios will operate in the ISM 920 Mhz band. After the mini-classes, each participant will design their RF component using NI AWR software. In the afternoon, the designs will be transferred to PCB via a simple “PCB in a bag” method and each component built and tested using a simple VNA. The workshop will conclude with a full radio test of at transmitter and receiver.

Participants need only a basic background in RF circuits, such as S-parameters and basic transmission line theory. Example designs will be available to ensure that everyone, form the most advanced RF designer, to the student can build a successful RF component. A prize will be given to the best performing system. The workshop will be taught by Prof. David S. Ricketts, who has taught this hands on Radio System Design course at Carnegie Mellon University and NCSU as part of a senior design course. Radio System Design is an open, online course that teaches students the basics of digital communication, RF system design, RF circuit design and finally fabrication and testing.

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A Bits2Waves receiver. From left to right: A 950 MHz patch antenna, a bandpass filter, a Wilkinson power splitter, two double-balanced mixers and a discrete LPF for the IF.  The LO is generated by a Branchline coupler to create 90 degree quadrature LO for QAM demodulation.

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AWR/NI VSS System Simulation Diagram of Radio. From left to right:

QAM Source generating I/Q signals. Upconverting mixers for I and Q with an LO at 950 MHz. A 90 degree phase shift separates the I/Q. I/Q signals are then combined and amplified and sent to the antenna.

The channel is modeled as a simple loss (no noise) for simplicity.

The received signal is filtered through a BPF and then split into two branches. These are downconverted using 90 degree phase shifted LOs to create the downconverter I and Q Signals.