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  • Writer's pictureNick Lansley

Radio Signals Are Beautiful: SDR and FM

As a radio ham I have recently become interested in a new branch of the hobby called Software Defined Radio (SDR). SDR is a radio system where the classic components of a radio receiver or transmitter has been replaced by a computer program,

It’s only in recent times that domestic computers have become powerful enough – and basic radio hardware cheap enough – to make this a reality. The magic of SDR is that, by replacing hardware components with software algorithms, fantastic new radio technologies are possible.

In my 10 year old Yaesu Ft-840 shortwave radio transceiver, hardware components do their best to allow me to receive the wanted radio signal and remove unwanted interference. In the world of amateur radios, often the most interesting, distant signals are the faintest. In global radio competitions such as Islands On The Air (IOTA), radio amateurs travel to distant islands with access using only low-powered equipment and less efficient radio antennas. Picking them us is a challenge due to their faintness amongst the cacophony of stronger signals. Often I fail to tune out interference because I can’t cut out the unwanted signals precisely using the hardware analogue filters in the radio.

In digital radio, I can use all kinds of computer processing power like a Swiss-army knife to precisely cut out interference and tune in the faint signal I want. Indeed, mathematicians are taking over from radio electronics circuit engineers in bring precision to radio in this way. Even better is that software-define radio returns radio engineering back into the hands of the hobbyist (admittedly one who can program!) to carry the frontiers forward. Compare that to the almost untouchable circuits deep in the heart of my (admittedly lovely) Yaesu FT-840 which I fiddle about with at my peril!

For us amateur radio enthusiasts it’s exciting times and I, for one, am engaging greatly with this new aspect of our hobby,

Yaesu FT-840 shortwave amateur radio transceiver

Above is the radio receiver dongle I use, based on the RTL2832+ R820T chipset. The antenna plugs into the side of the black USB stick which is a basic radio receiver insomuch as it receives a wide chunk of radio spectrum (without interpreting what it is picking up) and sends it straight into the computer.

In the image above, SDR software ‘SDRSharp’ receives and decodes (demodulates) BBC Radio 4 on 93.5 FM stereo in London from the USB stick shown above. It is this software doing the radio work (tuning to the radio signal, displaying it, decoding/demodulating it and sending the resulting audio to the PC speakers). In this case not only do I hear stereo sound, I also read the Radio Data Service (RDS) digital text giving the station name and the name of the show currently being broadcast or music track being played (depending on the station.

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