This is the first blog post of my RoadTest review of the Ettus USRP B205mini-i Software Defined Radio platform: Digilent 1x1 USB Software-Defined Radio Platform

1. Introduction


As a engineer and hobbyist I was always interested in Wireless Communication. In my projects I experimented with technologies like WiFi, BLE (Bluetooth Low Energy), GSM/3G/4G, GPS, LoRa, LoraWAN, SigFox and others.

 

Wireless communication for known technologies / protocols is usually implemented with specialized hardware (IC-s) implementing a specific wireless technology or protocol.

 

Software Defined Radio (SDR) on the other hand is a radio communication systems which supports receiving / transmitting on a wide range of frequencies using different radio protocols.

 

I got into Software Defined Radio just a couple of months ago, using a HackRF One (actually one of the AliExpress clones).

 

The plan for this RoadTest to compare the HackRF One with the Ettus USRP B205mini-i by building some RF applications.

 

2. The Ettus USRP B205mini-i

The USRP B205mini-i is a Software Defined Radio (SDR) device designed by Ettus Research, and apparently distributed by Digilent.

 

Before applying to this road test I knew little about Ettus Research, so I was a bit surprised when the device came in a generic National Instruments (NI) labeled box:

It turns out that Ettus Research is a National Instruments subsidiary, and since I last checked Digilent was also acquired by National Instruments.

 

The B205mini-i comes in some anti-static packaging, along with a USB 3.0 Type-A to Micro-B Cable and safety / getting started instructions:

The kit comes with no antennas, so we need to have some antennas with SMA connectors to get started. Fortunately, I got a set of antennas with the HackRF One kit I purchased.

 

In terms of specification the B205mini-i features:

  • a Frequency range: 70 MHz – 6 GHz
  • up to 56 MHz of instantaneous Bandwidth
  • Full Duplex operation
  • an user programmable Xilinx Spartan-6 XC6SLX150 FPGA
  • USB 3.0 connectivity

 

Here is a quick comparison between the USRP B205mini-i  and the HackRF One:

 

USRP B205mini-i

HackRF One

Frequency Range70 MHz - 6 GHz30 MHz - 6 GHz
Bandwidth56 MHz20 MHz

Sample size / rate

(ADC/ DAC)

12 bits / 61.44 Msps

8 bits @ 20 Msps

DuplexFull DuplexHalf Duplex
Programmable Logic Device

FPGA

Xilinx Spartan-6 XC6SLX150

(147K logic cells, 1,355 KB RAM, 180 DSP slices, etc.)

CPLD:

Xilinx XC2C64A-7VQG100C

(4 logic block, 64 macro-cells, 1500 gates)

Interface

USB 3.0

(5 Gbps)

USB 2.0 High Speed

(480 Mbps)

Cost~ 800 USD~ 150-300 USD

 

3. A First Application: FM Radio Receiver


To work with SDR devices we can use the GNU Radio the open-source radio platform.

On Linux is GNU Radio and appropriate drivers are fairly simple to install. We just need to run:

$ sudo apt-get install gnuradio
$ sudo /usr/lib/uhd/utils/uhd_images_downloader.py
$ sudo apt-get install hackrf libgnuradio-osmosdr0.2.0

 

and both the B205mini-i and the HackRF One should be ready to be used.

 

To create RF Applications we can use GNU Radio Companion app.

 

The GNU Radio Companion is a fairly simple graphical user interface (GUI) that allows building RF applications from a wide set of predefined components:

The above screenshot shows a simple FM Radio Receiver application:

  • in the first "row" we have a couple of variables (samp_rate, freq, gain, etc.) defined either as simple variables or as QT based UI controls
  • USRP Source component is used to interact with the Ettus B205mini-i and other devices from Ettus's USRP family
    • the frequency, gain, sample rate and bandwidth are tied to the variables defined above
  • the input signal from the B205mini-i goes to two components
    • QT GUI Frequency Sink is used to plot the input signal
    • a Rational Re-sampler is used to down-sample the signal from 1.92M to 192k
  • the FM Demodulation is the block that de-modulates the input signal, thus recovering the original base-band signal. It also band pass filtering and outputs an audio signal
    (source: Wikipedia)
  • a Multiply Const block is used to implement volume control based on a Volume UI control
  • finally the audio signal is fed into a Audio Sink responsible for playback

 

After connecting an antenna to the B205mini-i's RX2 port we should be able to run or application.

 

The antenna used bellow a generic antenna good from 48 MHz to 860 MHz:

 

The resulting RF Application looks like this:

Here is a quick video on how it works:

 

 

The same application ca be implemented on the HackRF One too. For this the USRP Source needs to be replaced with a Osmocom Source:

This is what it looks like with the HackRF One:

(note: osmocom source offers multiple gain adjustments. The Gain control from the UI controls the RF Gain)

 

In the next blog post I plan to do more experiments exploring different Wireless Protocols like the 434 & 868 MHz band protocols,  2.4 GHz protocols (BLE, WiFi), 5 GHz WiFi, etc.

 

Stay tuned!