RF Shorts for Aug. 9, 2013
Ofcom Engineer Creates Software-Defined DAB Radio System
I'm sure many readers have built their own low-power AM and FM transmitters and some have probably even built analog TV transmitters for use on the amateur radio bands. As analog modulation is disappearing in favor of more complex digital modulation technology, experimenters are using software instead of solder to construct digital radios. Ian Burrell describes one example of this in his article The squawking seagulls that could transform the radio industry--Engineer recorded birds to show DAB broadcasting could be done on shoestring - with software he downloaded for free
on the Independent.co.uk website.
“Mustapha, 38, is a spectrum engineer at Ofcom and the broadcasting regulator has published his work on Software Defined Radios (SDR) in an official paper which has been causing excitement among broadcasting industry executives and radio buffs this week.”
Mustapha constructed a DAB multiplex using free open source software and a Raspberry Pi computer and was able to broadcast it from Sussex Heights, a 102 meter tower block overlooking the English Channel.
Mustpha told The Independent, “This challenge had been bugging me for a while. It was difficult for me to accept that small local radio stations could never get a foothold on the digital platform. And there was frustration that the radio industry had not really done any work in the area.”
His experiment was “privately funded” with Mustpha spending about £3,000 of his own money in pursuing the project.
The Ofcom Report The potential for lower-cost transmitting stations in support of DAB rollout
provides detail on the software and hardware used in the testing. The description of the trade-offs involved should be useful for transmission formats beyond DAB.
Metamaterials Technology Explained
Lee Billings covers state-of-the-art metamaterial research in his article Exotic optics: Metamaterial world--Engineered structures with bizarre optical properties are set to migrate out of the laboratory and into the marketplace
on Nature.com. One of the technologies discussed is the Kymeta Ka-band satellite antenna that's built with metamaterials on a flat circuit board.
Billings writes, “At the heart of the antenna--the details of which are confidential--is a flat circuit board containing thousands of electronic metamaterial elements, each of which can have its properties changed in an instant by the device's internal software. This allows the antenna to track a satellite across the sky without having to maintain a specific orientation towards it, the way a standard dish antenna does. Instead, the antenna remains still while the software constantly adjusts the electrical properties of each individual metamaterial element. When this is done correctly, waves emitted from the elements will reinforce one another and propagate skywards only in the direction of the satellite; waves emitted in any other direction will cancel one another out and go nowhere. At the same time--and for much the same reason--the array will most readily pick up signals if they are coming from the satellite.”
He noted that “Kymeta has shared so few details of its antenna that researchers say it is hard to offer an evaluation” but adds physicist David Smith, director of metamaterials commercialization at Intellectual Ventures, is highly regarded in the field.
Billings also discusses metamaterial applications for optics, including very thin lenses for smartphones in his interesting article.
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