The XTRX: An Embedded SDR

Alasdair Allan
3 min readDec 15, 2017

Most people getting started with Software Defined Radios (SDRs) will pick up a cheap RTL2832U and R820T2 based RTL-SDR USB stick on Amazon for under $20. There are literally dozens of free and open-source software packages that support these ubiquitous cheap radios sticks making SDRs more accessible than they’ve ever been before.

The Fairwaves XTRX, now on Crowd Supply, is not one of these sticks. It’s something rather different because, as the creators put it “…if you’ve never used an SDR before, XTRX might be a bit overwhelming for you.”

The Fairwaves XTRX (📹: Fairwaves)

The XTRX is a compact Mini PCIe card SDR based around the Lime Microsystems LMS7002M FPRF. It has 2× 2 MIMO and has a tuning range of 10 MHz — 3.7 GHz, down to 100 kHz with some degradation, with a sample rate of up to 120 MSPS. It has a built-in GPSDO and an onboard FPGA, a Xilinx Artix 7 35T, which can be used to accelerate DSP tasks.

The XTRX board. (📷: Fairwaves)

The XTRX is part of a growing trend right now of productization of maker hardware. We’ve seen this before with things like the Raspberry Pi Compute Module.

This is an SDR designed to be a component, a black box to be slotted into a bigger build, rather than a build itself. LTE modems and GPS receivers are commodity parts, but integrating them together takes time. If the SDR isn’t the point of your project (or your product) but something that enables it, why take the time, when you can buy it off the shelf, and if a single XTRX can’t cover enough bandwidth?

The XTRX top (left) and bottom (right). (📷: Fairwaves)

Also available is XTRX PCIe Octopack, a full sized PCIe card loaded with eight XTRX boards, and a special board for synchronising all eight XTRX boards.

Bottom view of the XTRX PCIe Octopack. (📷: Fairwaves)

With synchronized clocks, multiple XTRX boards can collectively monitor very large chunks of the RF spectrum—eight synchronised XTRX boards can monitor nearly a full 1 GHz of bandwidth.

The basic XTRX board starts at $199, with free shipping inside the United States and an extra $10 for the rest of the world. However this does not include any cables, antennas, or adaptor boards. A set of antennas and cables— including four RF antennas (95 mm, 2 dBi, SMA male, GSM/3G/LTE 880–960 MHz, 1710–1990 MHz), one GPS antenna, and five cables— adds an additional $59. However if you’re thinking about picking up an XTRX PCIe Octopack? Things get a bit more expensive, that weighs in at $2,900.

The XTRX was successfully funded on Crowd Supply, and is expected to ship towards the end of May 2018.