Tagged: satellite

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you are installing hamlib for the AntRunner, you should do so from source as the packages in Ubuntu 22.04 appear to be out of date.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.

Detecting Starlink Satellites with a Portable Raspberry Pi + RTL-SDR

Over on his YouTube channel "saveitforparts" has in the past created a portable homemade 'tricorder' which was a boxed up Raspberry Pi with multiple sensors including an RTL-SDR. One new application he's found for the tricorder is the ability to detect the beacons from Starlink satellites using the RTL-SDR and an LNB.

Starlink beacons typically transmit at around 11.325 GHz, so to receive them with an RTL-SDR a downconverter and antenna such as an LNB is required.

In the video he demonstrates the hardware in use, and shows some of the beacons being received on the spectrum, via the tricorders built in LCD screen.

Detecting Starlink Satellites With DIY Tricorder

SatDump ReWork Release with Significant Feature and GUI Updates

SatDump is a popular piece of software that can be used with RTL-SDRs and other software defined radios for decoding images from a wide array of weather imaging satellites including GOES, GK-2A, NOAA HRPT, FengYun, Electro-L and Meteor M2 LRPT + HRPT, and many others (note: there is no APT support at the moment, but it is planned for the future). It is compatible with Windows, Linux and even has an Android APK available.

Recently author @aang23 has updated the software, noting that he's done an almost full rewrite, including major updates to the GUI. The SatDump blog post goes into greater detail about he updates, but as a summary some of the biggest updates include:

  • A reworking and tidy up of the GUI with improved FFT view
  • A viewer which allows you to view output image products, and create RGB composites
  • A projection tool on the viewer, allowing you to project images onto OpenStreetMap.
  • Upgrades to the plugins system, allowing developers to more easily add support for new satellites / missions and SDRs.
  • The addition of 'products' metadata, allowing users to separate raw channel data
  • The addition of demodulators like DVB-S2, GOES-R GRB, HimawariCast, DVB-S
  • Support for additional SDRs like BladeRF, SDRplay RSP Duo, PlutoSDR and MiriSDRs.
  • Updates to the CLI interface
  • Updated less buggy Android App
SatDump new Live Decoding / Recorder Interface

SATRAN MK3 Antenna Rotator Hardware Kit Released

Back in January 2021 we posted about the release of the SATRAN product, which is a low cost automatic motorized satellite antenna rotator kit. The rotator is deigned to be used for pointing high gain directional antennas such as a Yagi or satellite dish at low earth orbit satellites which can move across the sky quickly. They also supply an Android App for easily controlling the rotator.

Recently SATRAN MK3 (version 3) has been released a few days ago and costs € 175,00 for the kit, but does not include the plastic parts which need to be 3D printed. Unfortunately the kit appears to already be sold out, but we suspect they are working on getting more kits soon. Also of note is that they are based in Sweden and cannot ship to the US or Canada.

The email announcement reads:

"There's a new Satran in town!"

I'm glad to announce the newest Satran MK3 Rotator which is now available in the shop. The former cast aluminum version has been abandoned since the production was way too time-consuming and expensive.

The new MK3 has taken all the advantages of both older versions and returned to a more open source and 3D-printable design. This cuts the price by two thirds, while still getting a really user-friendly, compact and able device.

...and there's a new app!

Some users have reported issues with their Android app crashing, so today a new version of the app (2.3) has been finished and will be available in a day or two. If you don't get an update notification automatically in your app, visit Google Play to check for the latest version. 

The app also have a more extensive list of satellites and the possibility to search for a satellite by its Norad ID. 

SATRAN MK3 Antenna Rotator
SATRAN MK3 plastic parts that need to be 3D printed.

Open-Weather: A Browser Based NOAA APT Satellite Image Decoder

Thank you to Sasha Engelmann for letting us know about the release of the Open-Weather community's web browser based NOAA APT decoder. The decoder allows for easy NOAA satellite decoding by allowing you to upload a wav file recording of a NOAA satellite pass, and it will decode it into an image within the browser. 

The project emerged from a desire to understand the process of decoding APT audio recordings into NOAA satellite images, and a need for an accessible browser-based decoder for new practitioners during open-weather DIY Satellite Ground Station workshops.

While we were inspired by Thatcher's APT 3000, we felt accessibility, documentation and features could be expanded and improved. open-weather apt allows you to select an audio file on your computer, choose a demodulation method, add histogram equalisation and download images. The website does not store your personal data, including your location or any files you upload.

Documentation of the decoder is available on Public Lab here: https://publiclab.org/notes/sashae/05-03-2022/an-accessible-browser-based-decoder-for-noaa-images

open-weather apt is forked from Thatcher's APT 3000. It is a collaboration between open-weather, Bill Liles NQ6Z and Grayson Earle.
Open-weather web based APT decoder

APT_COLOR: Add False Color to Black and White NOAA APT Images

Thank you to Sasha for submitting news about the release of their latest application called "apt_color". The most popular application for decoding APT weather satellite images from NOAA polar orbiting satellites is WXtoIMG. However, WXtoIMG is closed source and is abandonware. There are APT decoder alternatives, however unlike WXtoIMG most other open source APT decoders only provide black and white images, and do not have a false color feature.

The apt_color application can be used to turn black and white APT images received from NOAA satellites into false color images. Sasha writes:

I am working on an APT false color application here. The application is still in the very, very, early stages but still seems to produce good results. It does not need to rely on any overlays, it simply works off the data you give it - the original decoded image data. I will attach some results. NOAA-18 seems to be the best suited spacecraft for this program.

apt_color: Turn black and white NOAA images into false color
apt_color: Examples

Lon.TV Demonstrates Decoding Various Digital Signals with RTL-SDR

Tech YouTuber Lon.TV has recently uploaded a video demonstrating how to identify and decode various digital transmissions with an RTL-SDR dongle. In the video he explains how to use VB Cable to pipe audio from SDR# into various decoders, and then goes on to show DMR, APRS, POCSAG, L-Band AERO, FT8, and JS8/JS8CALL all being decoded via an RTL-SDR Blog V3 dongle.

Software Defined Radio Part 2 - Decoding Digital Transmissions with an RTL-SDR USB Radio

Receiving Analog TV from Turkmenistan Unintentionally Bouncing off a Russian Military Satellite

Over on Twitter @dereksgc has been monitoring the 'Meridian' communications satellites, which are Russian owned and used for civilian and military purposes. The satellites are simple unsecure repeaters, meaning that actually anyone with the hardware can transmit to them, and have their signal automatically rebroadcast over a wide area. This has been taken advantage of recently by anti-Russian invasion war activists who have been trolling the satellite with SSTV images of the Ukrainian flag, as well as audio.  

Apart from intentional abuse, a side effect of being an open repeater is that sometimes the satellite can pick up powerful terrestrial signals unintentionally, such as analogue broadcast TV from Turkmenistan. Over on his blog, @dereksgc has written up an excellent post documenting the background behind this finding, his entire setup involving the hardware he's using and how he's aligning with the satellite, and what software he is using to decode the TV signal. In his hardware setup he notes that he uses a HackRF, but that a RTL-SDR would suffice.