A Portable RTL-SDR and Raspberry Pi Based ADS-B Alarm for Drone Pilots

Pilots of RC planes and drones need to be aware of the area they are flying in, to make sure that they stay well out of the path of manned aircraft. However, this can sometimes be difficult with aircraft like police helicopters that could rapidly show up anywhere. Drones typically do not have ADS-B transmitters due to size/weight and price, but it is still possible for drone pilots to use ADS-B receivers to make their flying safer.

Over on YouTube user xjet has come up with a solution involving the use of a portable ADS-B alarm for drone pilots. The ADS-B receiver consists of a 3D printed enclosure containing a Raspberry Pi Zero 2W, LCD screen and an RTL-SDR dongle connected to an ADS-B whip antenna. xjet notes that when his code and 3D enclosure are finalized, he will release the design for free as open source over on http://www.rcmodelreviews.com.

The idea behind the ADS-B alarm appears to be that drone pilots will receive an alarm when they are within the vicinity of an aircraft. Assuming the drone is not too far away from the pilot (as rules specify drones must be flown within visible distance) the alarm being next to the drone pilot should be sufficient. xjet notes that we cannot rely on live ADS-B aggregation websites like FlightRadar24 due to their censorship of certain aircraft like police, military and some private jets, or due to possible lack of coverage, so a local receiver will be a better solution.

After more than two years of development and testing the ADSB alarm for RC plane and drone flyers is almost ready to go. I will be posting the full build details including an SD-Card image, source code, wiring diagrams and STL/DWG files for the case to the RCModelReviews website in the next week or so. This is a totally open-source project which I give freely to the hobby community so as to increase the levels of safety associated with our activities.

It is through the use of this technology that we can show how taking practical steps towards ensuring safety is every bit as important (if not more so) than blindly following regulations written by those who have probably never even flown an RC plane or drone themselves.

This changes everything (I'm not kidding!)

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Guglielmo FM and DAB Receiver Software Updated to Version 0.5

Thank you to Marco, the programmer of Guglielmo for letting us know that his software has recently been updated to Version 0.5.

Guglielmo is a Linux, Windows (and in this recent update x86 MacOS) based RTL-SDR FM and DAB tuner software that supports SDRs including the RTL-SDR, Airspy, SDRplay, HackRF and LimeSDR. It is designed to be an easy to use program designed for media users, rather than hobbyist technical users.

Regarding the release of Version 0.5, Marco writes:

This release sports full mac (x86 only, sorry) and windows installers, DAB and FM scans and a preset editor.

Guglielmo: Screenshot of the DAB Interface
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Tech Minds: Building A Low Cost RF Power Sensor

Over on the Tech Minds YouTube channel Matt has recently showed us his build of DL5NEG's super simple diode based RF power sensor. The device is designed to detect and measure RF power, using a DC voltage meter and a calibration curve which converts the voltage detected by the diode into dBm. The simple diode based design is remarkably accurate, and could be a useful tool for testing or calibrating SDRs.

Matt's first build uses a simple copper PCB board, and although it is low precision the results he achieved match up pretty nicely with the calibration curves. In Matt's second implementation he created a proper PCB design using KiCad and PCBWay. After soldering the components with hot air, he found that the results were just as good when he tested the power output of his AntSDR E200.

Matt intends to use this sensor along with a simple ADC connected to a Raspberry Pi to measure the power going into his QO-100 setup via a -40 dBm coupler.

This story was also shown Hackaday. 

A Low Cost High Performance RF Power Sensor

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A GNU Radio DCF77 Time Signal Decoder

DCF77 is a long wave time keeping signal transmitting at 77.5 kHz from Frankfurt, Germany. It has been active since 1 January 1959. Using simple amplitude modulation, the signal encodes the current time and date, which is used by some devices like railway station clocks in Germany. Because it's a long wave signal transmitting at 50kW, it's possible to receive the signal across Europe, and sometimes even further away if propagation conditions are good.

Recently a DCF77 receiver and decoder program based on Python and GNU Radio has been uploaded to GitHub by henningM1r. It includes a simulator written in Python so you can simulate your own DCF77 signal for testing the receiver too.

Currently the decoder has been tested to work with an Airspy HF+ Discovery SDR, but it should work with any SDR capable of receiver 77.5 kHz if the GNU Radio source block is changed out.

DCF77 GNU Radio Decoder
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PySDR Guide on DOA & Beamforming

PySDR is a free online textbook created by Dr. Marc Lichtman which explains many digital signal processing (DSP) and software defined radio (SDR) concepts in a clear, concise and easy to understand way. The guide includes multiple images and animations, as well as Python code examples.

In a recent update, Dr. Lichtman has begun adding a new chapter on Direction of Arrival (DOA) and Beamforming which are core concepts for coherent radio direction finding devices like our KrakenSDR. As with the other chapters the guide is made easy to understand with many images and animations.

The introduction reads:

Direction-of-Arrival (DOA) within DSP/SDR refers to the process of using an array of antennas to estimate the DOA of one or more signals received by that array. Once we know the direction a signal of interest is arriving from, we can isolate it from other signals/interference/jamming.

It is just like isolating a signal in the frequency domain by filtering it, except we are now working in the spatial domain (you can certainly combine both!).

We typically refer to the antennas that make up an array as elements, and sometimes the array is called a “sensor” instead. These array elements are most often omnidirectional antennas, equally spaced in either a line or across two dimensions.

DOA is a subset of beamforming techniques, where as the receiver, we are trying to steer a beam (our receiver’s antenna beam) towards the direction of an emitter. We may also steer a beam blindly across a wide range (e.g., 0 to 360 degrees) to figure out what signals are being received and from what direction.

A visual example of what happens to two signals when the interelement spacing of a direction finding antenna array is reduced below half a wavelength.
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A Simulated Aircraft RADAR with Real Radar Scope Tube and ADS-B Data from an RTL-SDR

Over on YouTube we've found an interesting project by RingingResonance where he's created a simulated traditional radar scope using a real analog radar scope tube, and ADS-B data gathered from an RTL-SDR running dump1090 on a Raspberry Pi 3B.

The project uses a real radar scope tube which is controlled by SPI signals sent from the Raspberry Pi into a DAC, which is in turn connected to the analog radar scope. RingingResonance has uploaded the open source code to GitHub. He notes that the code currently pushes the Raspberry Pi 3 to it's limits, so the sweep speed is limited.

ADS-B Scope, My Real (Fake) RADAR Scope!

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Maverick-603 Project Suspended Indefinitely

Back in December 2022 we posted about the Maverick-603 which was at that stage Crowd Funding on Crowd Supply.

It was to be a US$149 FT8 receiver based on an open source RF chip design, capable of acquiring signals between 7 MHz and 70 MHz (technically 1 MHz to 100 MHz). Shipments were expected to begin in April 2023.

Unfortunately the Maverick team just released today that the project will be suspended indefinitely due to logistical issues. Backers of the project will receive a full refund.

The Maverick-603 project has been indefinitely suspended due to unforeseen logistical obstacles. No funds have yet been spent and all backers will receive full refunds. If you backed this project, your refund will be issued within the next week to the credit card you originally used. If your credit card is no longer valid, please contact Crowd Supply support before midnight UTC on Friday, April 28, 2023 to arrange your refund. If the Maverick-603 project is revived, we will post another update. Thank you for your support and patience.

The Maverick-603 FT8 Receiver
The Maverick-603 FT8 Receiver
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The RFNM: A Next Generation SDR with 10 MHz to 7200 MHz tuning range, 12-Bit ADCs and up to 612 MHz Bandwidth

The RFNM is an upcoming software defined radio that has some impressive high end specifications only seen in SDRs costing thousands, and at the same time the creator claims that it will be priced at a steal. While no pricing has been set, the creator noted in a Reddit post that pricing will be "closer to $500", bringing it's price similar to SDRs like the HackRF, bladeRF, LimeSDR, PlutoSDR.

The RFNM will have eight 12-bit ADCs on board, and provide up to 612 MHz of real time bandwidth for receiving. For transmitting it has two DACs, with up to 153 MHz of TX bandwidth. The tuning range will be from 10 MHz up to 7200 MHz. They note that their front end also has 13 preselection filters and six different LNAs and programmable attenuators.

Pushing 12-bit 612 MHz bandwidth of the device would be difficult, so to help with processing all that data, there will be an onboard VSPA DSP processor, as well as built in ARM CPU cores, and a 16 GFLOPS GPU. Connectivity will be either through USB 3.0, or Ethernet.

The main baseband chip on the SDR is the Layerscape® Access LA9310 chip sold by NXP which provides I/Q ADCs and DACs. Those signals are sent to the RFNM Daughterboard Interface, where they are upconverted to the frequency range of interest. This lets the end user choose a different daughterboard for different applications.

The Granita daughterboard has tuning capability from 600 MHz to 7200 MHz. To get frequencies down to 10 MHz the RFNM is making use of the RFFC2071A mixer. There will also be a cheaper 'lite' version that does not use a mixer, and hence only provides tuning from 600 MHz to 7200 MHz.

In addition, the website states that they are pursing a version of their board that will make use of the LimeSDR LMS7002 chip that will cover 10 MHz to 3500 MHz. They are also looking into boards that may break out more ADC lanes, an oscilloscope add-on, and breakout board.

You can join the RFNM email waiting list, and find more details about it at rfnm.io. At the time of this post they state that the waiting list is "53% full". As of right now the project appears to have nothing concrete to show off, but the lead creator Davide Cavion was behind the FPV Blue HD Video system, so he appears to have the experience to take this project forward.

A render of the RFNM software defined radio board.
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