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Open source BeagleBone SDR cape taps Xilinx Artix-7 FPGA

Mar 25, 2016 — by Eric Brown — 1,790 views

ValentFX is Kickstartering an open source FPGA-based and Linux-driven “KiwiSDR” BeagleBone Cape, that does 10KHz to 30MHz software-defined radio processing.

ValentFX has surpassed the 75 percent mark on its way to raising $50,000 on Kickstarter for its $199 KiwiSDR cape, which is due to ship in October. The campaign is also offering a $299 kit due in November that includes a BeagleBone Green SBC, a magnetic mount GPS antenna, and pre-installed KiwiSDR software with microSD card backup. The software-defined radio (SDR) system includes a Xilinx Artix-7 A35 FPGA, an ADC, and a 12-channel software-defined GPS receiver and front-end.

KiwiSDR BeagleBone cape
(click image to enlarge)

A BeagleBone Black is supported as well. However, the SBC’s mini-HDMI port, which is missing on the cheaper BeagleBone Green clone, can’t be used during SDR duty, as it causes interference.

Two more views of the KiwiSDR BeagleBone cape
(click images to enlarge)

ValentFX Logi-Pi

ValentFX knows its way around a BeagleBone — and an FPGA — as it proved with its Logi-Bone BeagleBone cape aimed at robotics and other applications that could benefit from the cape’s built-in Spartan-6 LX9 FPGA. The Newark Element14-distributed product line also includes a similar Logi-Pi add-on built around the Raspberry Pi and an FPGA education focused Logi-Edu.

SDR technology is used to process wireless communications tasks within software, offering easier reprogramming and reduced hardware expenditures in a world of quickly multiplying and changing wireless standards. ValentFX acknowledges that “the world doesn’t really need another SDR.” But then again, maybe it does. The company found a gap between low end “RTL-SDR USB dongle-style, or fixed DDC chip devices” with 8-12 bit ADC and limited bandwidth on the one hand and “full 16-bit SDRs” costing between $700 and $3500 on the other.

Even with the $299 KiwiSDR kit, which requires that you buy your own radio antenna and 5V power supply, this still adds up to considerably less than professional SDR gear. At the same time, the KiwiSDR cape delivers “better wide-band, web-enabled capabilities than the more expensive SDRs,” claims ValentFX.

With the KiwiSDR, an HTML5-capable browser can tune into a public KiwiSDR from anywhere in the world. The KiwiSDR supports a 10 kHz to 30 MHz frequency range, covering shortwave, longwave, narrow-band FM, AM, various utility stations, and amateur radio transmissions. Three prototypes are currently set up and casting away in Sweden, Canada, and of course, as befits a Kiwi, New Zealand.

The KiwiSDR offers a browser-based interface that enables up to four simultaneous user web connections per device with continuously adjustable bandwidths. Each connection can tune an independent receiver channel over the entire spectrum. The firmware is touted for tis waterfall display, which tunes independently of audio and includes zooming and panning. Other features include automatic frequency calibration via GPS timing.

KiwiSDR waveforms
(click image to enlarge)

The device is envisioned as a testbed for developing new applications that “utilize a significant number of programmable, web-accessible SDRs world-wide,” says ValentFX. The device’s GPS timing capabilities would enable direction finding, which the company calls “one of the great under-solved problems of shortwave listening, particularly for utility stations.” KiwiSDR might be used to solve this via time-of-arrival techniques, for example.

Another potential application would be a simple, streamlined data decoder built into the KiwiSDR web interface. The company has already prototyped a WSPR decoder using the device.

KiwiSDR block diagram
(click image to enlarge)

The “100% Open Source / Open Hardware / Open PCB” KiwiSDR cape features a multi-channel, parallel DDC design with bit-width optimized CIC filters, says ValentFX. The key hardware components are as follows:
  • Linear Technology 14-bit, 65MHz ADC
  • Xilinx Artix-7 A35 FPGA, programmed from the BeagleBone
  • 12-channel software-defined GPS receiver based on Andrew Holme’s Homemade GPS Receiver
  • Skyworks SE4150L GPS front-end

The open source firmware, with source code on Github, is based on the Linux-driven OpenWebRX stack. The server-side BeagleBone app is written in C/C++, with JavaScript on the browser and Verilog running the FPGA. The firmware is said to include ADPCM audio and waterfall compression to minimize required network bandwidth.

SDR is listed as a possible application for many, mostly FPGA-driven Linux gizmos we covered in recent years. Some SDR-specific devices that run Linux include Avnet’s $1,095 computer-on-module, as well as $1,800 PicoZed SDR Development Kit and Zedboard-based AD9361 SDR Evaluation Kit , which features an ADI transceiver module.

More expensive SDR devices include the $4,500 and up  Matchstiq Z1 from Epiq Solutions. Last year Epiq announced a still unpriced, handheld Matchstiq S10 model due to ship in the second quarter of 2016.

Further information

The KiwiSDR is available on Kickstarter through Apr. 16 for $199 for the BeagleBone cape alone or $299 with a BeagleBone Green, an enclosure, and a GPS antenna. More information may be found at the KiwiSDR product page, and more may eventually appear at the ValentFX website.

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