Where are all the new RF engineers? SDR to the rescueFollow article
Fifty years ago, amateur radio (a.k.a. ham radio) was a very popular entry point for youngsters to discover the magic of electronics. It went beyond the self-contained satisfaction to be had from building a guitar amp or a hi-fi system, because of the communication element. With radio, your finished project, however limited, provided endless fun chasing those elusive signals from around the world - where the state of the ionosphere, distance, frequency and time of day added to the technical challenges of the performance of the radio and antenna hardware. The impulse to constantly improve on the status quo was compulsive.
Forty years ago and the silicon chip was making an impact and the early home computers were starting to emerge. From then on, computing became more and more popular as an attractive techie hobby - suddenly there was software to write – this provided the challenge to achieve as much as possible with the processing power and memory limitations of the day. Winding forward in time; once the internet got going (culminating in Skype providing free global voice and picture communications), it appeared ham radio as a hobby had frozen in time, and was a thing of the past.
The result of this is that many of the people who really understand RF from a hands-on point of view, are an ageing bunch getting close to retirement. So how to revive interest in radio as a hobby?
Well, there is a growing recognition that maybe the internet isn’t as free and uncontrolled as it promised to be, and that wireless infrastructure has patchy coverage and can be fragile in times of emergency - so maybe it is becoming cool again to be able to ‘do your own thing’ with radio - but most powerful is the availability of low cost SDR (Software Defined Radio) technology - where your existing host computer can do all the hard work of demodulating and decoding the streams of data collected by this new breed of front-end radio receiver hardware.
The RTL-SDR Dongle
Recently, people have been using cheap ‘RTL-SDR’ dongles (designed originally so that PCs could decode digital TV transmissions) as SDR hardware. Freely available software such as ‘SDR#’, ‘HDSDR’ and ‘SDR Console’ together with a USB driver which can control the dongle and accept the stream of I/Q data are needed. It is then possible to tune across a wide range of frequencies (typically from 24MHz up to over 1GHz).
You can read more about RTL-SDR dongles here.
Which signals you select, and what you do with them is up to the user. Suddenly the software-savvy youngster with a PC can get into the driving seat of a universal radio for $20 of extra hardware! High resolution graphics allow them to visualise signals within a spectrum display, rather than having to know what frequency to choose.
Interestingly, once you have the ability to easily find and receive new and interesting frequencies, then you discover the fantastic work done by an ongoing core of dedicated hams and others. They have made accessible the demodulation, decode and computer interaction with every combination of analog and digital, data, voice and picture, satellite or terrestrial transmissions you could imagine. Affordable SDR is bridging those parallel universes of radio and computing and the result must be more innovation in the future.
However, SDRplay saw the potential of affordable SDR and decided to get involved. In particular they wanted to address these limitations:
- The dongles don’t cover below 24 MHz thereby missing out on short, medium and long wave reception
- The dongles use 8 bit ADC conversion technology which limits the dynamic range to around 45dB which is a lot worse than commercially available general coverage receivers.
- The dongles don’t include any front end filtering to help reduce ‘out of band’ interference.
The Radio Spectrum Processor – The RSP1
The RSP1 covers 10 kHz to 2 GHz, with simple ‘Antenna’ in and ‘USB’ out connectivity
The RSP1 uses 12 bit ADC technology from Mirics Ltd., who developed silicon capable of handling all global broadcast standards from Long Wave to L-Band. Because the chips were designed for use in cellular phones with serious power constraints and compromise antennas, the result is a radio which can perform as well as a traditional communications receiver, while allowing for up to 10 MHz bandwidth to be processed at a given time. 5th order Chebyshev filters ensure robust front-end filtering and reduce the effects of many out-of-band interferers.
The data sheet can be found here
As well as supporting popular 3rd party SDR software, SDRplay provide their own SDR programme called SDRuno which can be downloaded free of charge for use with the RSP1
SDRuno receiver software for Windows
SDRuno provides a rugged and flexible, high performance SDR receiver capability and boasts some excellent features:
- Multiple ‘Virtual Receivers’ which allow for simultaneous reception and demodulation of different types of signals within the same receiver bandwidth.
- A selectivity filter with an ultimate rejection greater than 140 dB.
- A unique distortion-free double stage AGC with fully adjustable parameters.
- Multiple notch filters with BW adjustable down to 1 Hz, Notch Lock feature.
- A unique synchronous AM mode with selectable/adjustable sidebands, dedicated PLL input filter, and selectable PLL time constants.
- SNR (stereo noise reduction), featuring a proprietary noise reduction algorithm for stereo broadcast.
- AFC for FM signals.
- Calibration for receiver frequency errors.
SDRplay also provide an open API so that developers can create completely new applications. As well as supporting Windows and MAC, there are versions for Android, Linux and Raspberry Pi 2/3.
Examples of decoding options (DRM, DSD+, Weather satellites, Dump1090, NBEMS, Wefax)
In the months since the RSP1 started volume production, SDRplay has seen a growing number of customers using the device for bespoke lab-based projects requiring an SDR radio – applications include anti-surveillance monitoring, remote wireless terminals, RFI detection, auto modulation-scheme detection, standards development, prototype IoT receiver chain design, satellite and weather balloon data gathering and various spectrum analysis applications. The compact design and ability to power over USB are particularly useful in portable set-ups.
At around $149, the RSP1 is perfect for undergraduate and research projects and a versatile and useful addition to any RF lab.