If you didn't know already Bitcoin is the top cryptocurrency which in 2017 has begun gaining traction with the general public and skyrocketing to a value of over $19,000 US per coin at one point. In addition to providing secure digital transactions, cryptocurrencies like Bitcoin are intended to help fight and avoid censorship. But despite this there is no real protection from the Bitcoin internet protocol being simply blocked and censored by governments with firewalls or by large ISP/telecoms companies.
One idea recently discussed by Nick Szabo and Elaine Ou at the "Scaling Bitcoin 2017" conference held at Stanford University is to use the something similar to WSPR (Weak Signal Propagation Reporting Network) to broadcast the Bitcoin network, thus helping to avoid internet censorship regimes. To test their ideas they set up a HackRF One as a transmitter and RTL-SDR and used GNU Radio to create a test system.
Over on his YouTube channel Kris Occhipinti has uploaded some videos where he shows how he is able to send text data over FM radio frequencies by using an MP3 audio file that encodes the text data, an FM transmitter connected to an Android phone or MP3 player to transmit the file and an RTL-SDR on the receiving side to receive the FM signal from the FM transmitter. The software used to encode the text into an MP3 is Minimodem, and on the receiving side Minimodem is also used which can easily decode the received audio. Minimodem is a command line program which can generate FSK modem tones from data.
These two videos are part of a series that Kris has been working on that includes many videos about using Minimodem to transfer data like text, files and images between computers via radio.
12 Minimodem an FM Transmitter and a USB SDR Dongle
HolyPager Art Installation. HackRF One, Antenna and Raspberry Pi seen under the shelf.
For a long time now it has been known that pager data is sent in the clear and in plain text over a strong and easily received RF signal. The signal can easily be intercepted with a standard scanner radio or more recently with an SDR such as the RTL-SDR. Software such as PDW can then be used to decode the signal into plain text. We have a tutorial on this available here.
In these more modern days of cell phones and secure text messaging very few people still use pagers. But one heavy user of pagers is the medical community who still prefer them as they are already widely implemented in hospitals and are very reliable. The lower frequencies and high transmission powers used by pager systems allows for better reception especially in areas prone to poor cellphone reception such as in big buildings like hospitals with many walls underground areas. They are also very reliable as they receive messages instantly, whereas text messages can be delayed in times of high network traffic which is obviously a problem when a doctor is needed urgently. Finally, another advantage is that most pagers only receive, so there are no local transmissions that could interfere with sensitive medical machines. A major downside however is that pager use means that a lot of very private patient data can be easily intercepted by anyone anywhere in the same city as the hospital.
Back in October artist and programmer Brannon Dorsey displayed an art installation at the Radical Networks conference in Brooklyn which he calls Holypager. The idea is to bring attention to the breach of privacy. The installation simply prints out the pager messages as they are sent in real time, accumulating patient data that any visitor can pick up and read. He doesn't mention it on his page, but in one of the photos we see a HackRF One, antenna and Raspberry Pi hiding underneath the installation which is how the pager messages are received. A simple RTL-SDR could also be used as the receiver. Brannon writes:
Holypager is an art installation that intercepts all POCSAG pager messages in the city it resides and forwards them to one (holy) pager. The installation anonymizes all messages and forwards them randomly to one of three pagers on display. Each message is also printed on a contiguous role of receipt paper amassing a large pile of captured pages for gallery goers to peruse.
Pagers use an outdated protocol that requires all messages to be broadcast unencrypted to each pager in the area. It is the role of the individual pager to filter and display only the messages intended for its specific address. The pagers below have been reprogrammed to ignore this filter and receive every message in the city in real time. Today, these devices are primarily used in hospitals to communicate highly sensitive information between doctors and hospital staff.
Given the severity of the HIPPA Privacy Act, one would assume that appropriate measures would be taken to prevent this information from being publicly accessible to the general public. This project serves as a reminder that as the complexity and proliferation of digital systems increase the cultural and technological literacy needed to understand the safe and appropriate use of these systems often do not.
Thanks to Dr. Celalettin Uçar from Turkey for submitting a video of the work done by a PhD student who as part of his research created an RTL-SDR based ground penetrating radar simulation and metal detector. He writes:
This apparatus (YAĞRIN) was created with rtlsdr in a phd work. We achieved detecting a metal gasoline tube from the depth of aproximately 1 meters. Furthermore, we created the time domain signal and ploted the reflaction from the metal with using the matlab (simulink) model.
A video on YouTube is linked which we display at the end of the post. They write that the system consists of a 12V DC supply, step down voltage regulator, ADF 4350 programmable signal generator, 25W power amplifier (470 MHz, 45 dBm signal power), Philips omnidirectional antennas (RX,TX), a 64 dB low noise amplifer and an RTL-SDR and computer to display the output. The software he uses is SDR# which appears to simply listen for a tone and detect any changes that occur when something metal moves near it. The PC also runs a MATLAB Simulink model which we believe helps detect metal signatures by plotting the reflection.
In the past we posted about a similar but simpler metal detector implementation by Ancient Discoveries.
RTL-SDR BASED GPR (Simulation) & METAL DETECTOR (YAĞRIN) - Dr. Celalettin UÇAR
Many homes in the US and elsewhere no longer require meter reader personnel to come onto the property to read a physical meter at the back of the house. Instead the meter transmits wireless data in the 900 MHz ISM band about electricity usage, and all the meter reader has to do is turn up outside the house and take a reading from the street.
These electricity usage signals are unencrypted and can easily be decoded and displayed with an RTL-SDR and a ready to use program called rtl_amr. The signals even travel quite far, and there have been reports of receiving neighbours signals up to 600m away. K-roy took his RTL-SDR and rtl_amr and wrote on top of it a program that creates a JSON output of the data for easy processing, a PHP, SQLite3 and JQuery based database system for storing the data, and an HTML5 based page for graphing and displaying the data.
Over on Hackaday.io we've come across a project by "Tom" who has created a small tracking device which is located using an RTL-SDR dongle and directional Yagi antenna. The tracking device itself is a simple fingernail sized low power UHF transmitter that transmits short pulses about every second or so in the 915 MHz ISM band. Tom writes that the range is about 400m (line of sight) and with a small button cell battery the device lasts a couple of days with its 180 uA current draw. Presumably longer operation could be achieved by significantly reducing the pulse rate of the circuit.
To receive the tracking device an RTL-SDR is combined with a high gain directional Yagi antenna, a three level 10 - 30 dB attenuator and an Android phone running the RF Analyzer app. The idea is to simply use the attenuator and directional Yagi antenna to determine the direction in which the signal is strongest. That direction with the strongest signal will indicate where the transmitter is. Tom's video below shows an example of the transmitter and RTL-SDR based tracking setup.
Recently the SDR# team have updated the algorithm on the noise reduction plugins used in SDR#. It appears that both the IF and Audio noise reduction plugins were updated with a better smoothing algorithm. We briefly tested the new algorithm and compared it against an older version. The new algorithm has noticeably less hiss and is slightly clearer when compared at the same noise reduction level. We tested with the same threshold levels and using the speech profile.
At the same time we've also seen news that Simon of SDR-Console is working on another noise reduction algorithm based on deep neural networks in the latest private beta version. A video of it in action was posted by Paul J in the SDRplay users group (note that you will need a Facebook account and will probably need to be a member of the SDRplay group to view that video). The algorithm seems to be based on the RNNoise paper that was posted here. The SDR# algorithm was also tweaked based on information gained from that paper although it doesn't use neural networks directly.
If you are in the USA, you might recognize HD Radio (aka NRSC-5) signals as the rectangular looking bars on the frequency spectrum that surround common broadcast FM radio signals. These signals only exist in the USA and they carry digital audio data which can be received by special HD Radio receivers. Earlier in the year in June a breakthrough in HD Radio decoding for SDRs like the RTL-SDR was achieved by Theori when he was able to piece together a full HD Radio software audio decoder that works in real time.
It turns out that some of these HD Radio signals run by iHeartRadio also contain other data streams such as live weather and traffic data that is consumed by HD Radio based car GPS receivers or audio head units in US vehicles. HDRadio.com also write that they can embed other data such as sports scores and emergency messages into the data stream as well.
KYDronePilot's Python script utilizes Theori's decoder to save all received weather and traffic data maps for a folder. Below is an example of traffic and weather data that he received.
HD Radio Received Traffic DataHD Radio Received Weather Data
