Software Defined Radio (SDR) and Field-Programmable Gate Arrays (FPGA) — A Free Radio Scanner

When I was grow­ing up, one of my favourite birth­day presents was a Uniden UBC3000XLT radio scan­ner. I enjoyed find­ing and lis­ten­ing to var­i­ous radio trans­mis­sions, and I had some suc­cess decod­ing data trans­mis­sions and morse code using my PC and Sound Blaster soundcard.

Uniden UBC-3000XLT Radio Scanner
Uniden UBC-3000XLT Radio Scanner

I was inter­est­ed to read about a tech­nique called Soft­ware Defined Radio (SDR), which can sam­ple the entire short­wave spec­trum, and use the pro­cess­ing pow­er of a com­put­er to vir­tu­al­ly ‘tune’ in to transmissions.

A home-built SDR board oper­at­ing at the Uni­ver­si­ty of Twente in the Nether­lands (pic­tured below) and a receiv­ing ele­ment around 5cm x 10cm is capa­ble of receiv­ing a fre­quen­cy range of 0 — 29.160 MHz.

It uses a Spar­tan XC3S500E Field-Pro­gram­ma­ble Gate Array. FPGAs can be pro­grammed using a hard­ware descrip­tion lan­guage, and arrays of pro­gram­ma­ble log­ic blocks which can be vir­tu­al­ly inter-wired. The most impor­tant advan­tage over a micro­con­troller like a Atmel/Arduino, is these oper­a­tions can hap­pen in par­al­lel, which is crit­i­cal to cre­at­ing a soft­ware defined radio, as a typ­i­cal AVR micro­proces­sor sim­ply does­n’t have the nec­es­sary clock speed. The sam­ple rate must be at least twice the max­i­mum fre­quen­cy of the sig­nal (Nyquist theorem).

PA3FWM Software Defined Radio
Soft­ware Defined Radio at the Uni­ver­si­ty of Twente

Tak­ing this a step fur­ther, Soft­ware Defined Radio can allow mul­ti­ple users to share the same receiv­er. At time of writ­ing, 184 users are lis­ten­ing to dif­fer­ent fre­quen­cies using the receiv­er at the University.

You can lis­ten for your­self at the Wide-band Web­S­DR at Uni­ver­si­ty of Twente. It’s essen­tial­ly a free radio scan­ner any­one can access for free. You might enjoy stum­bling upon a vari­ety of trans­mis­sions from all over the world, and you may have suc­cess using tools like Sor­cer­er to decode data trans­mis­sions, weath­er fax trans­mis­sions, and morse code.

With the ever-con­tin­u­ing advances in data stor­age capac­i­ties and scal­able clouds, one day it may be a triv­ial mat­ter to archive the entire radio fre­quen­cy spectrum.