Over on the SWLing post, Thomas has shared an interesting video showing aircraft scatter reception in action. Alps DX [FR] shows on his YouTube channel a broadcast FM signal coming in clearly as a plane passes by, then fading away to nothing as it leaves. This effect is due to the scattering of radio waves that occurs when radio waves reflect off aircraft.
In order to predict when the scattering occurs he uses the free AirScout software which allows you to do the following:
Calculate a propagation path as a cross circle path between two QSO – partners
Calculate a path profile between both QSO – partners using a Digital Elevation Model
(DEM)
Calculate the mutual visibility of an aircraft from both QSO – partners for each point on the path using their elevation and any possible obstruction between them
Calculate a “hot area” in which an aircraft is mutually visible from both QSO –
partners where a reflection is theoretically possible
Show calculated path and aircrafts in real time on a map
Predict Aircraft Scatter potential for each single aircraft according to position, track and altitude
Outernet's moRFeus is a signal generator and frequency mixer that can be controlled either by it's built in LCD screen, or via software on a Windows or Linux PC. It can generate a clean low phase noise tone anywhere between 85 to 5400 MHz. Because it can be computer controlled it is possible to use moRFeus as a tracking generator for characterizing filters and measuring antenna SWR. A tracking generator is just a signal generator that can be set to output at the same frequency that the measurement receiver is tuned to.
In the past we've posted about some software developed by Ohan Smit, which allows a moRFeus to be controlled on a Windows/Linux PC via a nice GUI. Recently he's updated the software and it can now draw power (dbFS) graphs for characterizing filters when combined with an Airspy and TCP comms to GQRX. Ohan writes:
So when you press sweep, it detects if there is any TCP servers on port 7356 and if so tunes the radio and gets a power measurement and after the sweep is done, morfeusqt renders a graph on the fly.
It now also supports multiple devices, no configurations required. It just opens another window for the second device.
These features thus far work on both Windows 10 and Ubuntu 18.04.1, these are my two testing environments with GQRX and the Airspy.
Ohan also notes that he's working on several new features such as the ability to plot VSWR, remote control of the moRFeus via TCP, support for multiple SDR TCP protocols such as rtl_tcp, soapytcp etc, threading and progress bars, as well as possibly support for cheap Osmo-FL2K devices as a tracking generator.
You can follow his developments live on the Outernet forums.
moRFeus used as a tracking generator with an Airspy with the morfeusQT software
A while ago we posted about Osmo-FL2K which is a Steve M Osmocom project that allows you to use a cheap $10 USB to VGA adapter as an HF - 1.7 GHz transmitting SDR. Now another similar project by Ted Yapo has been released which allows the use of a low cost FT232RL based USB to Serial Port adapter as a transmit capable SDR. It appears that the FT232RL via harmonics is able to transmit up to at least 27 MHz, and possibly higher.
A USB To Serial Port adapter being used as a transmitting SDR
The basic implementation is similar to the idea used by RPiTX - that is to modulate the square wave output of a TX pin to generate an arbitrary signal at a desired frequency. Of course this results in numerous harmonics which must be heavily filtered if ever actually transmitting with some power or high gain antenna.
In his hackaday.io project log, Ted shows that he's been able to transmit AM audio at 1 MHz, and has also been able to control an RC toy at 27 MHz. For the RC toy controller he's also created a simple BPF in order to reduce the harmonics. In addition to the FT232RL chip, he's also tried other serial chips like the CP2102N but found that the signal produced was not as clean.
Othernet (previously known as Outernet) are currently having a 50% off sale on all their products. This means that you can snag a discounted Dreamcatcher at only US$75, and a moRFeus at US$99. The sale expires midnight on the 26th.
The sale is exclusive to RTL-SDR Blog readers (although feel free to share the coupon) and the coupon code to use at checkout is rtlsdrblog83759.
Dreamcatcher and Othernet Data Signal Information
If you weren't already aware, the Othernet project aims to bring live data such as news, weather, video, books, Wikipedia articles and audio broadcasts to the world via a free satellite service and cheap receivers. Although an internet connection provides the same data, Othernet's satellite broadcast is receivable in remote areas, will continue working in disasters, and costs nothing to continually receive roughly 200MB of data a day. The trade off is that the service is downlink only, so the data that you get is only what is curated by the Othernet team.
Othernet can provide this service for free because they are funded by private customers whom they provide private data/audio satellite channels to. One such private customer is attempting to implement an Othernet based Tsunami early warning system in Vanuatu which would work even when the cell phone system fails in a disaster. Each siren is equipped with an Othernet receiver and LNB that receives the Othernet signal. The goal is to allow for any village to be able to set up their own low cost warning system. At the same time the Othernet Tsunami warning receiver is made use of in normal circumstances as it receives a satellite radio broadcast which is then re-transmitted to the village over regular FM radio.
Currently the public service is in a test period and is only available in North America, but public service for the EU and possibly Oceania is planned to begin in Q1 2019. The rest of the world should eventually follow after. Some more information about the data service can be found on our previous post.
Alternatively, if you have no interest in the data service then your Dreamcatcher could also be used as a TX/RX capable LoRa radio. In a previous post we had some fun with two Dreamcatchers and a LoRa chat application.
Othernet Dreamcatcher
moRFeus Information
The moRFeus is a low cost signal generator. It's capable of generating a tone anywhere from 85 MHz to 5400 MHz, and it can also be used as a frequency mixer component for implementing things like homebrew upconverters and downconverters.
Over on YouTube user Petr Horký has uploaded a helpful tutorial video showing how to install GNU Radio on Windows 10. Petr goes through the steps from installing Python, pip and other dependencies like numpy and pyqt, to installing GNU Radio itself and then ensuring that the system PATH is set correctly.
GNU Radio is a block based programming language for building digital signal processing applications (e.g. demodulators/decoders). It is very useful for experimenting with more advanced SDR concepts, and there are also many RTL-SDR compatible applications built with GNU Radio as well. GNU Radio is typically run on Linux, but can also run on Windows now too, although perhaps not every program will be compatible.
How to install GNU Radio Companion on Windows 10 (pip, environment variables)
Recently JJ wrote in and wanted to share his multi-feature living room radio that he's created with a Raspberry Pi, RTL-SDR, and various software packages installed on the Pi. Previously we posted about his cute LegoPi radio, and this living room radio is an iteration on that.
The radio is able to tune into live broadcast FM via an RTL-SDR and the NGSoftFM software, and also can be remotely access with SpyServer. It can also tune into internet radio, or play MP3 files. He's also installed Google Assistant and Alexa onto the Pi, so it can work as a digital assistant too. The features and software he uses are noted below:
FM / DAB+ / Internet radio with random mode / MP3 player / Google assistant / Amazon Alexa / SPYserver (SDRsharp), all controlled with a USB keypad or a Bluetooth remote control.
Internet radio VLC (https://www.videolan.org/vlc/index.html) The random internet radio part is a lot of fun to use. You can do random by genre or just random everything. Reminds me when turning the MW dial at night when I was a kid and not knowing what was coming next! It is just a python script that fetch the icecast directory then populate a small SQL database on the pi. I used this (https://github.com/ksc91u/icecast_play) as a starting point.
MP3 player VLC. I used a 16GB SD card on the pi (good compromise between speed of boot versus capacity). The whole system takes a little bit less than 5GB, which means I have 10GB+ for MP3 files.
SPYserver More a gadget than a serious tool because I'm using a wire for antenna (on the last radio) but has proven to be usefull to help position the wire for optimum FM / DAB+ reception by looking at the spectrum and play with the dongle gain in SDRsharp (https://airspy.com/spy-servers/).
Bluetooth remote control I used a PlayStation 3 (PS3) bluetooth remote since the pi 3 has bluetooth built-in. Easily available in used video game stores and very cheap, the remote works very well but it took me a while to get it going. This page helped: https://www.mythtv.org/wiki/Sony_PS3_BD_Remote
Last but not least, the radio is a complete Linux environment so I can connect to it from my Win10 box via SSH (https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html) and play with all the RTL-SDR goodies, even GNU Radio :-) providing you install a desktop environment (for ex. PIXEL) on top of Raspbian Stretch Lite.
For a while now researchers at MIT and several other universities have been investigating methods for using frequencies in the WiFi bands to see through walls using a form of low power radar. The basic concept is to track and process the reflections of these signals from peoples bodies.
Recently researchers at MIT have taken this idea a step further, combining the radar results with machine learning in a project they call RF-Pose. The result is the ability to recreate and track full human post information through walls. The abstract from their paper reads:
This paper demonstrates accurate human pose estimation through walls and occlusions. We leverage the fact that wireless signals in the WiFi frequencies traverse walls and reflect off the human body. We introduce a deep neural network approach that parses such radio signals to estimate 2D poses. Since humans cannot annotate radio signals, we use state-of-the-art vision model to provide cross-modal supervision.
Specifically, during training the system uses synchronized wireless and visual inputs, extracts pose information from the visual stream, and uses it to guide the training process. Once trained, the network uses only the wireless signal for pose estimation. We show that, when tested on visible scenes, the radio-based system is almost as accurate as the vision-based system used to train it. Yet, unlike vision-based pose estimation, the radio-based system can estimate 2D poses through walls despite never trained on such scenarios.
The hope is that this technology could one day be used as a replacement for camera based computer vision. It would be a non-intrusive method for applications like gaming, monitoring the elderly for falls, motion capture during film making without the need for suits and of course for gathering data on peoples movements.
It is not mentioned in the paper, but it is likely that they are using some sort of SDR like a USRP for receiving the signals. It's possible that a lower resolution system could be set up cheaply with a HackRF and some passive radar software.
RF Pose Estimating Human Pose Behind walls using RF signals in the WiFi frequencies.Multiple people tracked with RF-Pose
Over on YouTube the Ham Radio 2.0 channel has recently uploaded a talk that Scotty Cowling (WA2DFI) did at the 2018 TAPR digital communications conference. His talk centers around single board computers and his findings on the nine best single board computers (SBC) for ham radio SDR setups.
Scotty's talk begins by discussing why you'd want to use SBCs in your ham radio SDR setup, and explains why you might want to place them with the SDR close to the antenna, and then distribute the data over ethernet cable. He then reviews 9 boards listed below:
Hardkernel Odroid C1
Raspberry Pi 3B
Hardkernel Odroid XU4
ASUS Tinker S
FriendlyElec NanoPC-T4
Pine64 RockPro64
96 Boards Mediatek X20
96 Boards HiKey 960
UDOO X86 Ultra
The boards are compared against CPU clock speeds, architecture, cache, debut year, RAM, boot ROM, bus speeds, OS support, and more. Scotty also discusses the need for low latency operation, but is yet to compare this on the boards. The best value for money boards that Scotty recommends end up being the Odroid XU4, Tinkerboard, NanoPC-T4 and the RockPro64.
Ham Radio 2.0: Episode 151 - Evaluating 9 of the Best Single Board Computers for Modern SDR Systems
