Not too long ago we posted about Jacek Lipkowski (SQ5BPF)'s project called "Etherify" which seeks to use unintentional RF radiation from Ethernet hardware/cables to transmit arbitrary signals such as morse code and FSK. During his earlier experiments he noted how he felt that the Raspberry Pi 4 had an unusually strong radiated Ethernet signal. In his recent post Jacek investigates this further.
On Wednesday Nov 11 Noon Pacific time, Hackaday will hold a hack chat (group text chat session) with Marc Lictman, author of the free online book "PySDR: A Guide to SDR and DSP using Python". We posted about the release of this book last month, noting that it is probably one of the best books in terms of explaining DSP fundamental concepts in an easy to understand way. Hackaday write:
“Revolution” is a term thrown about with a lot less care than it probably should be, especially in fields like electronics. It’s understandable, though — the changes to society that have resulted from the “Transistor Revolution” or the “PC Revolution” or more recently, the “AI Revolution” have been transformative, often for good and sometimes for ill. The common thread, though, is that once these revolutions came about, nothing was ever the same afterward.
Such is the case with software-defined radio (SDR) and digital signal processing (DSP). These two related fields may not seem as transformative as some of the other electronic revolutions, but when you think about it, they really have transformed the world of radio communications. SDR means that complex radio transmitters and receivers, no longer have to be implemented strictly in hardware as a collection of filters, mixers, detectors, and amplifiers; instead, they can be reduced to a series of algorithms running on a computer.
Teamed with DSP, SDR has resulted in massive shifts in the RF field, with powerful, high-bandwidth radio links being built into devices almost as an afterthought. But the concepts can be difficult to wrap one’s head around, at least when digging beyond the basics and really trying to learn how SDR and DSP work. Thankfully, Dr. Marc Lichtman, an Adjunct Professor at the University of Maryland, literally wrote the book on the subject. “PySDR: A Guide to SDR and DSP using Python” is a fantastic introduction to SDR and DSP that’s geared toward those looking to learn how to put SDR and DSP to work in practical systems. Dr. Lichtman will stop by the Hack Chat to talk about his textbook, to answer your questions on how best to learn about SDR and DSP, and to discuss what the next steps are once you conquer the basics.
Over on his channel popular electronics YouTuber Andrea Spiess has uploaded a tutorial video showing how to properly use a NanoVNA V2. The NanoVNA V2 is a vector network analyzer which can be used to measure and tune things like antennas, filters and cables. In the video Andreas aims to explain the differences between the VNA, Spectrum Analyzer and VSWR meter, what you can measure with a VNA, how to read the VNA results, the limitations of cheap VNAs, why and how to calibrate, and a review of the overall quality.
Andreas explains these concepts in a very easy to understand way, so this video is a great start if you've ordered a NanoVNA.
How to properly use a NanoVNA V2 Vector Network Analyzer (Tutorial)
Thank you to a few readers for suggesting a post about the "tinySA". The tinySA is a low cost standalone spectrum analyzer which was made recently available from Chinese manufacturer "Hugen" who was the manufacturer that popularized the original NanoVNA. It can be found on Aliexpress for about $49 shipped worldwide. R&L also have US based stock available. The official specs from tinysa.org/wiki read:
Spectrum Analyzer with two inputs, high quality MF/HF/VHF input for 0.1MHZ-350MHz, lesser quality UHF input for 240MHz-960MHz.
Switchable resolution bandpass filters for both ranges between 2.6kHz and 640kHz
Color display showing 290 scan points covering up to the full low or high frequency range.
Input Step attenuator from 0dB to 31dB for the MF/HF/VHF input.
When not used as Spectrum Analyzer it can be used as Signal Generator, MF/HF/VHF sinus output between 0.1MHZ-350MHz, UHF square wave output between 240MHz-960MHz.
A built-in calibration signal generator that is used for automatic self test and low input calibration.
Connected to a PC via USB it becomes a PC controlled Spectrum Analyzer
Rechargeable battery allowing a minimum of at least 2 hours portable use
A spectrum analyzer allows you to view a defined slice of the frequency spectrum on a graph. It does not allow for demodulation of signals. We note that SDRs like the RTL-SDR could be used as a spectrum analyzer too with software like QSpectrumAnalzyer and Spektrum, however the advantage of the tinySA is that it is a standalone package with it's own screen that can easily be used in the field. Unlike an SDR extra computing devices like a computer or smartphone are not required.
Over on YouTube IMSAI Guy has been uploading a few videos reviewing the tinySA. From his videos he found a few issues including a slow update rate, harmonics and high phase noise. However, later he finds that most of the harmonic issues disappear as long as the input signal level is kept below -30dBm. In some more recent videos he also finds a fault with the attenuator chip on one of his tinySA units and repairs it by replacing the chip.
Evariste (F5OEO) has just announced the release of an update to RPiTX which allows it to now be used on a Raspberry Pi 4. If you are unfamiliar with it, RPiTX is a program for Raspberry Pi single board computers that allows you to transmit almost any type of signal on frequencies between 5 KHz up to 1500 MHz with nothing more than a piece of wire connected to a GPIO pin. Evariste also notes that the new version is compatible with the beta 64-bit version of Raspbian.
Some examples of signals you can transmit with RPiTX include a simple carrier, chirp, a spectrum waterfall image, broadcast FM with RDS, SSB, SSTV, Pocsag, Freedv and Opera. You can also use an RTL-SDR to record a signal, and replay the IQ file with RPiTX. However, please remember that transmitting with RPiTX you must ensure that your transmission is legal, and appropriately filtered.
Numbers Stations are mysterious radio broadcasts that typically consist of a voice speaking a seemingly random string of numbers. It is mostly accepted that these stations are a way for spy agencies to communicate to intelligence operators stationed overseas.
However, recently Simon Roses wrote in and wanted to share his project where he created his own numbers station at home. The idea is to use a Raspberry Pi and the Pi-FM-RDS software to transmit a simulated numbers station. If you didn't already know, a Raspberry Pi can be used as a somewhat useful RF transmitter by using software like Pi-FM-RDS which manipulates a GPIO pin connected to a piece of wire acting as an antenna.
In his write up, Simon notes that he uses a program called PiNumberStation which is a text to speech program that passes the generated voice to Pi-FM-RDS. Pi-FM-RDS then transmits the signal, allowing a nearby FM radio to pick up and play the audio.
If you wanted to try this as a prank or joke, please remember that transmitting in the FM bands over a certain power level may be illegal in some countries, and the Raspberry Pi TX capabilities are known to require filtering to prevent interference occurring on other frequencies. Transmitting incorrectly could have dire consequences, so please make sure you do your research first.
In the past we've posted about the Dictator Alert project a few times, as it makes use of ADS-B data contributed to ADS-B Exchange via volunteers who typically run an RTL-SDR as part of their ADS-B reception hardware. The project aims to track the movements of Dictators around the world via their use of private jets that can be tracked via ADS-B logging.
Over on Reddit the leader of the project Emmanuel has posted asking for donations. If you think this is a worthy project, please consider donating.
I'm raising some funds for our www.dictatoralert.org project which tracks aircrafts used by dictatorships all over the world (using SDR!). You can see all of the tracking for free on the website and several twitter bots (London, Paris, Geneva, EuroAirport).
Dr. Marc Lichtman has recently released his free online PySDR guide to Digital Signal Processing (DSP) explained with the help of software defined radio and Python code. Over the years we've seen numerous SDR & DSP courses come out, some requiring payment and some free. We note that this guide is completely free, and appears to be one of the better if not the best guide in terms of explaining DSP fundamental concepts in an easy to understand way. A lot of visualizations and animations are used which really help anyone new to the subject.
While the explanations are very good, please note that this is still a technical University level guide intended for Computer Science or Engineering students, so prerequisite knowledge is required. Dr. Marc recommends it for someone who is:
Interested in using SDRs to do cool stuff
Good with Python
Relatively new to DSP, wireless communications, and SDR
A visual learner, preferring animations over equations
Better at understanding equations after learning the concepts
Looking for concise explanations, not a 1000 page textbook
The SDR hardware used in the book examples is the PlutoSDR which is a fairly low cost SDR intended for use by students. However, the PlutoSDR isn't required as most of the code examples use generated data.