Whitepaper: SDR - Boosting the Flexibility of RF Communication

Software-defined radio (SDR) offers an alternative design approach compared to traditional radio frequency (RF) design techniques. This article explores how SDR enables engineers to build radios that can react more readily to interference, employ more sophisticated channel-coding schemes to increase data rates, and take advantage of other advanced RF technologies.

Modern homes are dense with radio signals, mostly from Wi-Fi, cellphone, TV and radio. Though not a lot, it’s free energy and it prompted EW BrightSparks 2018 winner Chaoyun Song from Liverpool University to investigate if the hands of an electronic clock can act as antennas for capturing the wireless energy from ambient signals, possibly to help power smart sensors and IoT/IIoT devices. The result of Chayun’s research was a battery-free quartz clock with wireless sensing functions.

Software Defined Radio allows you to create receivers for any radio signal. You just need a single peripheral connected to your personal computer. HackRF One, is such a SDR peripheral, connected through USB. It receives or transmits signals from 1 MHz to 6 GHz. Designed to enable test and development of modern and next generation radio technologies, HackRF One is an open source hardware platform that can also be programmed for stand-alone operation.

Thanks to 3D imaging sensor technology, the Walabot RF short-range scanner with its 15 RF antennas detects tubes, lines, wires and cables behind walls. Walabot works like a radar. It transmits radio waves and receives their reflections. The RF scanner generates a 3D image of the environment in real time and displays it on a monitor. Depth, type of material and position are also determined. Walabot even detects moving rodents that may be hiding in dry walls.

Radio remote controls for model aircraft and similar devices are rightly subject to strict regulations. They govern not only the transmit frequency, but also (and primarily) the transmitter power output. With the RF power meter described here, you can easily check how much power you are transmitting, at frequencies up to 10 GHz.

Researchers from the University of Washington have developed fully-3D-printable objects capable of transmitting status information to a receiver without requiring energy or electronic parts. Surfing on Wi-Fi signals objects like containers can send information about the amount of product left inside them to a system and automatically order a refill.

Antennas are back magic to many electronicists and to hear that antennas may detune in the presence of metal is a further argument to leave all that “RF wizardry” to the specialists. And you can, safely. Antenova, winner of an Elektra 2017 award, can now supply a 2.4-GHz antenna which is designed to operate without de-tuning on metal surfaces or where the product housing is mainly metal. The antennas from the ‘Reflector’ range consist of two layers, one electrically isolated from the other, so as to provide RF shielding to the second layer. As a result the antenna can be placed on any kind of material and it will radiate effectively in the direction pointing away from the base material.

PIN diodes are typically used in RF circuits as switches and attenuators. Acting as charge-controlled variable RF resistors, they perform in most cases better than FETs, exhibiting low insertion loss, high isolation, and excellent power handling and linearity. The impedance of a PIN diode can go from an almost open circuit to an almost short circuit.

When dealing with radio-frequency signals it often comes in handy to have an easy way to attenuate a signal level in discrete steps. For example, you might want to reduce the output of an RF generator to a lower level than the output control on the generator allows, and there are many other applications of attenuators in the adjustment and repair of receivers and other radio equipment. Unfortunately professional attenuators are rather pricey, but they do not contain any expensive electronics and so a DIY approach is an eminently practical alternative.

The requirement for high-speed design has brought about a number of design challenges never associated with low-speed devices. The ever increasing clock speeds have transformed digital switching circuits into RF generators, which is critical and not easy for the PCB layout task. Other factors which may occur at higher speeds in the embedded system are signal and power integrity problems due to impedance variations caused by switching problems or overheating. The good news: the limited functionality required from embedded systems permits these to be designed for much more efficient performance.