rtl_fm / rx_fm: Allows you to decode and listen to FM/AM/SSB radio. rtl_sdr / rx_sdr: Allows you to record raw samples for future processing. rtl_power / rx_power: Allows you to do wideband scans over arbitrarily wide swaths of bandwidth by hopping over and recording signal power levels over multiple chunks of spectrum.
rx_tools is based on SoapySDR which is an SDR abstraction layer. If software is developed with SoapySDR, then the software can be more easily used with any SDR, assuming a Soapy plugin for that particular SDR is written. This stops the need for software to be re-written many times for different SDR’s as instead the plugin only needs to be written once.
Nuand is the company responsible for the bladeRF software defined radio. The bladeRF x40 is a SDR that usually costs $420. It uses a LimeMicro LMS6002D chip, which has a 12-bit ADC and a tuning range of 300MHz – 3.8GHz.
For one day only they have released a special price for the bladeRF x40 of $199 USD, for the first 50 customers only. At the time of this post the deal still seems to be active, and the coupon code of “MHZ” is still working. Of note is that the recently successfully crowdfunded LimeSDR uses the newer and better LimeMicro LMS7002M chip, so Nuand may be testing the waters for a lower price point on their bladeRF. However, one thing to note is that the bladeRF is proven hardware with active software applications, whereas the LimeSDR is not yet proven.
Nuand also recently released an update which saw the source released for an ADS-B decoder that can be run on the bladeRF’s onboard FPGA, and also an update which allows the bladeRF to display up to 124 MHz of bandwidth at any one time. The large bandwidth display appears to work in a similar way to rtl_power or SpectrumSpy for the Airspy, by quickly switching between multiple chunks of frequency. The difference is that the bladeRF can do this by using onboard HDL accelerators which allow it retune extremely fast at several thousand times a second.
To reverse engineer the drones wireless communications system the teams used software defined radios like the HackRF and BladeRF, and also an alternative method involving just using an Arduino and nRF24L01+ receiver chip. Once the signal was received, they used GNU Radio to decode the signal into packets of data. After analyzing the data they found that the data bytes were easily reverse engineered and then were able to transmit their own data packets to control the drone. The post goes into further detail on the specifics of the reverse engineering.
Last month we posted about an experimenter who showed us a tutorial on how to use an RTL-SDR and rtl_entropy to generate random passwords. Now another experimenter, Sean Cassidy has used a BladeRF to generate entropy and used it to seed /dev/random. In the post Sean explains what /dev/random is, and how important it is to provide a good entropy source in Linux, or risk having encryption keys discovered.
He writes that Linux usually gets entropy from activity such as mouse movements, network activity or even hardware random number generators that are available on some Intel CPUs. However, he mentions that hardware random number generators are likely to be back doored by the government for spying purposes and so cannot be trusted. To get around this Sean decided to use his BladeRF as a hardware random number generator, but he also writes that the RTL-SDR will also work.
The set up simply involves installing the software brf_entropy, or rtl_entropy for the RTL-SDR, and then using the “rngd” command to sample randomness for /dev/random from the BladeRF’s output.
The programmer of Linrad (aka Leif sm5bsz) has uploaded a video to YouTube that compares several software defined radios on dynamic range and compression performance in the presence of strong nearby signals. In the video Leif tests the Airspy, BladeRF with B200, FDM-S1, Funcube Pro+, rtlsdr/E4000, rtlsdr/FC0013, rtlsdr/R820T, SDR-14 and SDRplay.
The main test works by tuning to a broadcast band FM frequency and then injecting a strong carrier signal at distances of 500 kHz, 1 MHz, 2 MHz and 5 MHz from the center frequency. The carrier signal strength is slowly increased until the SDR shows signs of complete degradation of reception of the FM signal. Better SDRs will tolerate stronger nearby signals without degradation.
The results are summarized at 34:20, 1:21:38 and 1:48:30. We have also taken screencaps of the results at 1:21:38 and 1:48:30 and they are shown below. The first column is when a higher gain is used, and the second column is when a lower but still barely copyable gain level is used. In the Levels for loss of performance columns smaller numbers are better and in the Dynamic range columns larger numbers are better. Finally, at the end of the video starting at 1:45:55 Leif also tests the spur performance of the SDRs.
Using an RTL-SDR Clayton Smith was able to reverse engineer his remote controlled ceiling fan. To do this he first used his BladeRF to determine that the remote control was transmitting a signal at 303.747 MHz. He then used a simple GNU Radio flow graph with the RTL-SDR to plot the amplitude of the signal over time which suggested that the signal was using on-off keying. From the plot he was then able to visually determine the bit pattern sent from each button on the ceiling fan remote.
Next he used his bladeRF and another GNU Radio flowgraph to replicate and transmit the the bit pattern which was able to control the ceiling fan from the PC.
Clayton notes that all this reverse engineering was done in half an hour, demonstrating the power of software defined radio.
The newer Linux kernels have DVB-T support for the RTL2832U chip, so the latest version of Ubuntu 13.10 will be able to recognize the RTL-SDR stick as a DVB-T receiver easily. Clayton used VLC in Ubuntu 13.10 to receive the DVB-T signal transmitted by the BladeRF which was tested on the 70cm, 33cm and 23cm bands.
The HackRF, BladeRF and USRP are all high end SDRs which range in cost from $300 (HackRF) to $1100 USD (USRP B210). They differ from the RTL-SDR in that each is specifically designed for the purpose of software defined radio, and they all have large bandwidths and transmit capabilities.