Category: Applications

AntRunner: Testing A Low Cost Satellite Antenna Rotator

Weather satellites that transmit HRPT give you high resolution uncompressed images of the earth. With an SDR, L-band feed, 60 cm or larger satellite dish and LNA+filter these images can be received by anyone. Derek OK9SGC has the definitive HRPT reception tutorial available here. However, as these are low earth orbit satellites, the user is required to find a way to track the satellite as it moves across the sky. With some skill and experience, hand tracking can work, but a motorized solution is really what is desired. Other applications such as ham satellite communications as well as radio astronomy projects may also benefit from motorized tracking .

Antenna rotators that rotate in azimuth and elevation can be used to track satellites moving across the sky. The problem is that antenna rotators are typically very expensive, or are a major task to DIY, involving circuit construction and 3D printing of parts.

Recently on Tindie we came across the "AntRunner" which is a relatively low cost portable antenna rotator from China coming in at US$325 with free shipping to most countries (VAT is added for the EU as $50 in shipping fees).

AntRunner is based on two geared stepper motors, a motor controller PCB and an open frame. AntRunners code is open source, as well as some partial hardware schematics.

It can be interfaced via a USB serial connection or through WiFi via it's onboard ESP32 chip, and it relies on the Hamlib 'rotctl' software library running on either the controlling PC, or another intermediary device like a Raspberry Pi. Once setup, software like Gpredict on the PC or Look4Sat on Android devices can be used to control the rotator.

The AntRunner: Low cost antenna rotator
The AntRunner: Low cost antenna rotator

AntRunner Tests

We ordered an AntRunner for testing with our own funds. Our setup involved a USB connection from the AntRunner to a Raspberry Pi, 12V plug pack and a 60cm dish. We installed hamlib on the Raspberry Pi, and used Gpredict (PC) and Look4Sat (Android) on networked devices to send the desired elevation and azimuth commands to hamlib on the Raspberry Pi for particular satellites.

(Note that if you are installing hamlib for the AntRunner, you should do so from source as the packages in Ubuntu 22.04 appear to be out of date. And the older version of hamlib installed via Ubuntu does not support the AntRunner).

Overall the AntRunner works as expected and was easily able to follow HRPT satellites across the sky. It was also great for easily pointing and switching between geostationary satellites like GOES and GK-2A. It easily held and moved a 60cm dish and feed which weighs about 3 kg. The specs of the AntRunner indicate 5 kg max load (although the GitHub specs note 10kg), so it should be able to hold larger diameter dishes as well.  

However we did have an issue with the advertised WiFi connection which is an alternative to the USB serial connection. When connected to WiFi the connection would always drop after a single movement command was sent, and it would never reconnect unless rebooted twice. For this reason we abandoned WiFi and only used the USB serial connection, and communicated wirelessly via the Raspberry Pi. There is also a WiFi web interface available for testing movement commands and setting up the WiFi connection, but it is only in Chinese.

It's possible that RF noise from the motors was causing the WiFi disconnection, but on the frequencies that L-band satellites operate at, we did not notice any motor interference.

The AntRunner is advertised as a portable rotator, so that means it is not suitable for use in poor weather as it has no cover to protect the motor circuit board and motors themselves from rain. However, it is certainly small and light enough to be portable. You just need a portable 12V power supply as well. 

Another issue is that when power is lost, the motors will spin freely, resulting in the antenna coming crashing down fast. So care must be taken when powering down with someone there to hold the antenna. The user is also required to physically hold the antenna level at 0 degrees elevation before powering up the AntRunner, so that it will reference 0 degrees elevation. Once powered the antenna holds in place.

There are also no limit switches on the device, so if an erroneous command is sent, it could send the motors into a position that could damage something.

AntRunner (Image from Tindie)
AntRunner (Image from Tindie) (NOTE: The tripod stand is not included)

Conclusion

Overall if you want something cheap and pretty much ready to use out of the box for tracking HRPT or other LEO satellites, the AntRunner is a good budget choice if you intend to only setup temporary stations. It is not suitable for permanent satellite receiver setups, at least not without some modifications.

A similar product is the SATRAN MK3 which was a 3D printed kit costing 175 Euros + shipping, but unfortunately this product appears to no longer be sold.

The ultimate in low cost rotators is probably the SatNOGS V3 rotator, but as mentioned this is a DIY project that requires a significant time commitment as it involves 3D printing multiple parts, sourcing components, building PCBs and constructing everything together. We have found one company offering a SatNOGs hardware kit, containing all of the parts required for US$445.

A commercial option might be the Yaesu G-5500DC which goes for US$759.95 on HRO, however you also need the GS-232 Rotator Computer Controller for computer control which is an additional US$589.95. Update: We've been informed that there are also cheaper third party computer controllers for Yaesu rotators, such as the CSN Technologies S.A.T Rotator Controller which sells for US$278.

Tech Minds: Testing a Radiosonde Decoder Plugin for SDR++

In one of his latest YouTube videos, Matt who runs the Tech Minds YouTube channels has posted a demonstration of the Radiosonde decoder plugin for SDR++ called sdrpp_radionsonde.

SDR++ is a software defined radio receiver program that is compatible with almost every SDR, including the RTL-SDR. Like other SDR programs, is has plugin capability, allowing third parties to develop additional features like decoders.

In the video Matt first shows how to install the plugin, demonstrates it being used with an example RS-41 radiosonde, and then shows how to use the log file outputs like the GPX track file on a free GPX map plotting website.

Radiosonde Decoder Plugin for SDR++

A radiosonde is a small sensor and radio package normally attached to a weather balloon. Meteorological agencies around the world typically launch two balloons a day from several locations to gather data for weather prediction. With an RTL-SDR, appropriate antenna and decoding software it is possible to decode the telemetry signal and gather the weather data yourself. You can also use the GPS data to chase and collect the fallen radiosonde package. We have an alternative tutorial on setting up a basic radiosonde decoder in Windows here.

Real Time Speech to Text from Radio Speech via DragonOS, SDR4Space, Mosquitto and WhisperCPP

Real time high quality speech to text is now possible with OpenAI's WhisperCPP, a high-performance and open source automatic speech recognition model.

In his latest video on YouTube, Aaron demonstrates how to use his latest DragonOS image to transcribe audio from a radio voice channel that is received with an RTL-SDR. He makes use of SDR4Space as the command line receiver, WhisperCPP as the AI transcriber and Mosquitto for monitoring WhisperCPP outputs and displaying the text to the terminal.

Here's a short video showing exactly how to setup and run SDR4space in such a way that real time IQ captures are demodulated and feed to WhisperCPP (High-performance inference of OpenAI's Whisper automatic speech recognition (ASR) model) for transcribing.

The latest DragonOS FocalX R28 comes w/ everything needed to do exactly what I show in this video, to include a sample tiny model.

You'll noticed in the video that jobs are placed in a queue for continued captures and results are also sent over to Mosquitto MQTT where a client can see messages as they are created.

I chose to use an RTLSDR v3 dongle for the capture, but it's possible to configure SDR4space to use a variety of soapy supported SDRs.

In his first video Aaron shows how to get setup with the system on DragonOS. Shortly after uploading his first tutorial, Aaron noticed that recompiling WhisperCPP on the local system yielded a significant decrease in the processing time of the AI. After recompiling locally the transcribing then became near real time. In the second video Aaron briefly demonstrates the real time transcription. 

DragonOS FocalX Capture and Transcribe IQ w/ SDR4space/WhisperCPP/Mosquitto (RTLSDR, OpenAI)

DragonOS FocalX Captured IQ to Text Faster w/ SDR4space/WhisperCPP/Mosquitto (RTLSDR)

In the past we posted a similar project that was based on the Amazon Transcribe cloud service. However WhisperCPP runs on a local machine, is open source and seems to be at least as good as Amazon Transcribe. So this appears to be a significant leap in transcribing ability and we could see it being used to automatically create text logs and alerts based on various radio channels.

Tech Minds: Running the SDR++ Multiplatform Server on MacOS, Windows and Raspberry Pi

SDR++ is an open source receiver program compatible with most software defined radios including the RTL-SDR that has been going through rapid development making it now one of the top software choices. In runs on almost every platform, including Windows, Linux, MacOS and Android.

One feature that SDR++ has is it's remote server. This is similar to applications like rtl_tcp which allow an SDR on a remote device like a Raspberry Pi to be accessed over a network.

Over on YouTube, Matt from Tech Minds has uploaded a video showing how to run the SDR++ Server on MacOS, Windows and Raspberry Pi platforms.

SDR++ Multi-Platform SERVER

Watch Duty: California Wildfire Watch Driven by RTL-SDRs

Over on Hackaday we've seen an interesting post about the non-profit "Watch Duty" wildfire reporting smart phone app for Californians. Several populated regions of California are extremely prone to wildfires, and it's important that residents get timely notifications about nearby wildfires so they can evacuate early and/or prepare their defensible spaces.

Often by the time official notifications have gone out, it is too late. To solve this, the approach Watch Duty takes is to have volunteers monitoring public safety radio channels, and ADS-B aircraft positions in order to gather information in real time. Once critical information is established, the watch duty volunteer can push out a notification via the smart phone app. 

The volunteers make use of receiver stations that consist of multiple RTL-SDR dongles with each dongle monitoring a different EMS radio system, and one additional RTL-SDR is used for ADS-B aircraft monitoring of helicopters and fire fighting aircraft. The stations appear to uplink radio data to the volunteers via a cellular modem or Starlink.

Earlier in the year Popular Science and Wired reported on Watch Duty as well, but did not mention the use of RTL-SDRs.

A Watch Duty monitoring station with multiple RTL-SDR Blog V3 dongles.
A Watch Duty monitoring station with multiple RTL-SDR Blog V3 dongles.

KrakenSDR Locates a Repeater Jammer in 1 Hour

Over on YouTubem channel NotaRubicon Productions has uploaded a video describing how a KrakenSDR was used to find the location of a person jamming a repeater site. Amateur radio enthusiasts can utilize VHF or UHF repeater towers, which receive signals from lower power handheld or other radios, and retransmit that signal at high power on a slightly different frequency over a much wider area. Unfortunately malicious people can jam these repeaters by transmitting at the same time as other users, effectively denying use of the repeater by legitimate users.

If you weren't already aware, KrakenSDR is our 5-channel coherent radio based on RTL-SDRs, and it can be used for applications like radio direction finding. We successfully crowd funded the device on Crowd Supply, and the device is currently available for sale on Crowd Supply, Mouser and direct from our website krakenrf.com.

In this video I read the story of how we caught the jammer that had been jamming our GMRS repeater for months, and how by using the KrakenSDR Radio Direction Finder (RF locator), we were at his house in 1 hour.

The KrakenSDR can track a signal being transmitted from 100Mhz to 1Ghz - so I can track ham repeater jammers, GMRS repeater jammers, ham-radio transmitters, GMRS radios - pretty much any transmitter with a signal strong enough for you to receive.

How The KrakenSDR Located Our Repeater Jammer In 1 Hour. Overview of the KrakenRF Inc. RF Locator

uSDR Updated to Version 1.6.0

Thank you to Viol for submitting news about the latest update of his uSDR software. uSDR (aka microSDR) is a lightweight general purpose multimode program for Windows that supports the RTL-SDR, Airspy, BladeRF, HackRF and LimeSDR radios. Viol highlights the latest features in the new update below: 

  • Airspy HF+ Discovery frontend support
  • ExtIO*.dll interface support. Copy ExtIO*.dll and all dependencies to the root folder and have a fun
  • ExtIO_USRP.dll and all dependencies for USRP B210 included. Just install Zadig libusb driver and go
  • LimeSDR multiple frontends switch fixed
  • FM demodulator with inverted audio spectrum
  • DCS decoder
  • additional C/C++ source examples for remote IQ passband processing TCP client
  • advanced IQ file playback options
  • display hold peak spectrum mode, zoomable and panable plot, customized colors

As always all descriptions, screenshots and binaries could be found on 

https://sourceforge.net/projects/u-sdr/

uSDR aka microSDR. A lightweight SDR receiver program for Windows.

DEF CON 30 RF Talks: Biohacking, Designing Antennas, Tracking Military Ghost Helicopters and More

DEF CON is a yearly conference with a focus on information security. At this years DEF CON 30 conference various talks on RF related topics were presented. In the past few weeks talks have been uploaded to YouTube for all to watch. Below we highlight a few we found interesting. The list of all main talks can be found on the Defcon YouTube channel, and talks from the RF Village can be found on the RF Hackers Sanctuary YouTube page. 

J9 - Biohacking Using SDR When You Don’t Know What You’re Doing

Security Researcher and BioHacker J9 presented an interesting and entertaining talk about how she used an SDR to listen in and decode a wireless pH sensor pill she ingested as part of a medical test.

What would you do if you were implanted with a medical device that broadcasts every 12 seconds?

Starting with loads of curiosity and very little knowledge about RF, how to use a software defined radio (SDR), and no knowledge of how to decode captured RF signals, I embarked on an adventure to teach myself something new. Jumping head first into the RF CTF helped greatly!

This presentation starts with cocaine and ketamine (in a controlled medical setting) and includes a near-death experience and new skills attained by building on the work of those who came before me. The end result of this adventure led me to the US Capitol to sit down with Senate staffers about the security and exploitability of medical devices.

DEF CON 30 RF Village - J9 - Biohacking Using SDR When You Don’t Know What You’re Doing

Erwin Karincic - Have a SDR? - Design and make your own antennas

In this talk Erwin Karincic explains how to design and make custom PCB antennas using home based or low cost techniques.

Most Software Defined Radios (SDRs) process a wide range of frequencies usually ranging from few MHz to multiple GHz where different antennas are used to pick up signals in a specific subset of that range. All applications using SDR require antennas to operate efficiently at very specific frequencies. Most inexpensive commercial antennas are designed either for wider ranges with lower gain over the entire range or very specific known frequencies with higher gain. The problem occurs when the researcher performs an assessment of a device and requires the use of specific frequency for which an antenna with high gain is not readily available. Most security researchers within wireless domain have outlined that their specific attack or exploit could be executed at higher range if antenna had better gain at that specific frequency. This talk focuses on bridging that gap by providing a way for researchers to create their own patch antennas without deep electrical engineering experience.

DEF CON 30 RF Village - Erwin Karincic - Have a SDR? - Design and make your own antennas

Andrew Logan - Tracking Military Ghost Helicopters over Washington DC

In this talk Andrew explains how ADS-B receivers, combined with ATC communications, public announcements and crowd sourced visual identification have helped track the activity of military helicopters operating over the Washington DC area.  

There's a running joke around Washington D.C. that the "State Bird" is the helicopter. Yet 96% of helicopter noise complaints from 2018-2021 went unattributed: D.C. Residents can not tell a news helicopter from a black hawk. Flight tracking sites remove flights as a paid service to aircraft owners and government agencies; even in the best case these sites do not receive tracking information from most military helicopters due to a Code of Federal Regulations exemption for "sensitive government mission for national defense, homeland security, intelligence or law enforcement." This makes an enormous amount of helicopter flights untraceable even for the FAA and leaves residents in the dark.

What if we could help residents identify helicopters? What if we could crowd source helicopter tracking? What if we could collect images to identify helicopters using computer vision? What if we could make aircraft radio as accessible as reading a map? What if we could make spotting helicopters a game that appeals to the competitive spirit of Washingtonians? And what if we could do all of this... on Twitter?

DEF CON 30 - Andrew Logan - Tracking Military Ghost Helicopters over Washington DC