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.
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.
I've published a summary on how I received the analog TV broadcast via a Russian military satellite using an SDR, as well as the short story leading up to it.— derek (@dereksgc) March 27, 2022
Check it out if you're interested!https://t.co/mgCScsDEgP pic.twitter.com/1Oeokg3MYB
Recently on Twitter @arvedviehweger (Arved) has tweeted that he has successfully received images from the Russian Arctic monitoring satellite known as ARKTIKA-M1, via it's X-band downlink at 7865 MHz. We've reached out to Arved and he's provided the following information on his setup and how he's receiving and decoding the images.
My first good picture from the ARKTIKA-M1 satellite on 7865 MHz!— Arved - DK5AV/MØKDS (@arvedviehweger) January 1, 2022
It appears that the satellite downlink is a lot stronger now which allows me to finally get a clean decode. I really hope it will stay that way! pic.twitter.com/qy7HDA2uAP
The Arktika-M1 satellite is a Russian weather satellite which operates in a HEO orbit. It was launched in February 2021 and has downlinks on multiple bands. The main payload downlink for the imagery is on 7865 MHz (which is also known as the lower X-Band). The satellite only transmits imagery on the X-Band at the moment, it is currently unknown whether it will ever transmit any image data on L-Band.
For Amateur reception that means having access to X-Band RF gear. It usually consists of a low noise pre-amplifier and a downconverter to convert 7865 MHz down to a lower frequency for easier reception with a high bandwidth SDR such as the LimeSDR, a USRP etc.
In my personal setup I use a surplus pre-amplifier made by MITEQ (around 36dB of gain, 1dB NF), my own self-made DK5AV compact X-Band downconverter and a LimeSDR-USB.
My L-Band gear is now mounted on top of my X-Band gear which allows me to do both at the same time 🙂 I will probably try that on FY3B in the future. pic.twitter.com/SFdy04EwuT— Arved - DK5AV/MØKDS (@arvedviehweger) July 27, 2021
The L-Band gear is mounted on top (helix and the pre-amp behind it) and the X-Band gear is right below. From left to right you can see the feed, the downconverter (silver box) and the LNA (mounted to a heatsink and a fan). Recording is done with a LimeSDR-USB running at a sample rate of 50 MSPS. The satellite transmits every 15 minutes once it reaches its apogee, each transmission including the idle period lasts for about 10 minutes. Some pictures of the idle transmission and the actual data transmission can be found in this Tweet, [noting that Idle = more spikes, actual data looks weaker]:
Some FFT screenshots of the actual signal! pic.twitter.com/TDHHDRchDF— Arved - DK5AV/MØKDS (@arvedviehweger) January 1, 2022
Depending on the geographical location a rather large satellite dish is also required for Arktika-M1. Reception reports all over Europe clearly show that the satellite has a beamed antenna (similar to ELEKTRO-L2).
In my setup I can get away with a 2.4m prime focus dish (made by Channel Master) in North Eastern Germany. It produces around 9 - 10 dB of SNR in the demod of @aang254’s excellent SatDump software. Anything above 5dB will usually result in a decode but since the satellite does not have any FEC you will need more than that for a clean picture. (Image of SNR in Satdump)
Over on his blog Derek (OK9SGC) has recently uploaded a very comprehensive beginners guide to receiving HRPT weather satellite images. HRPT reception can be a little daunting as it requires a good L-Band dish setup which involves choosing and building a feed, and importantly, a way to track the satellite with the dish as it moves across the sky. Tracking can be achieved manually by hand, but that can be very difficult and so a motorized tracking mount is recommended.
This is unlike the much easier to receive NOAA APT or Meteor LRPT satellite signals in the VHF band which can be received by a V-dipole antenna, or the geostationary GOES HRIT satellites that can be received with a WiFi grid dish and LNA. Both of which do not require tracking.
The advantage of HRPT however, is that you end up with high resolution, close-up, and uncompressed images of the earth. For example Derek notes that NOAA APT gives 4km/px resolution, and Meteor LRPT gives much better 1km/px resolution but it is heavily compressed. Whereas HRPT gives peak resolutions of 1km/px uncompressed. There are also nine satellites in operation sending HRPT, so there are more opportunities to receive.
Derek has created a very comprehensive beginners guide that covers almost everything from purchasing and building the hardware, to finding and tracking the satellites, to setting up the software and decoding images. He notes that an RTL-SDR can be used as the receiver, and that a WiFi dish with GOES SAWBird LNA can work, although the difficult tracking requirements are still there so a smaller offset dish with custom helix feed might be preferred. Derek also provides useful tips, like the fact that the NOAA15 HRPT signal is quite a lot weaker than others.
SDRAngel is a general purpose software defined radio program that is compatible with most SDRs including the RTL-SDR. We've posted about it several times before on the blog, however we did not realize how much progress has occurred with developing various built in plugins and decoders for it.
Thanks to Jon for writing in and sharing with us a demonstration video that the SDRAngel team have released on their YouTube channel. From the video we can see that SDRAngel now comes stock with a whole host of built in decoders and apps for various radio applications making it close to an all-in-one SDR platform. The built in applications include:
- ADS-B Decoder: Decodes aircraft ADS-B data and plots aircraft positions on a map
- NOAA APT Decoder: Decodes NOAA weather satellite images (in black and white only)
- DVB-S: Decodes and plays Digital TV DVB-S and DVB-S2 video
- AIS: Decodes marine AIS data and plots vessel positions on a map
- VOR: Decodes VOR aircraft navigational beacons, and plots bearing lines on a map, allowing you to determine your receivers position.
- DAB+: Decodes and plays DAB digital audio signals
- Radio Astronomy Hydrogen Line: With an appropriate radio telescope connected to the SDR, integrates and displays the Hydrogen Line FFT with various settings, and a map of the galaxy showing where your dish is pointing. Can also control a dish rotator.
- Radio Astronomy Solar Observations: Similar to the Hydrogen line app, allows you to make solar measurements.
- Broadcast FM: Decoding and playback. Includes RDS decoding.
- Noise Figure Measurements: Together with a noise source you can measure the noise figure of a SDR.
- Airband Voice: Receive multiple Airband channels simultaneously
- Graves Radar Tracker: For Europeans, track a satellite and watch for reflections in the spectrum from the French Graves space radar.
- Radio Clocks: Receive and decode accurate time from radio clocks such as MSF, DCF77, TDF and WWVB.
- APRS: Decode APRS data, and plot APRS locations and moving APRS enabled vehicles on a map with speed plot.
- Pagers: Decode POCSAG pagers
- APRS/AX.25 Satellite: Decode APRS messages from the ISS and NO-84 satellites, via the built in decoder and satellite tracker.
- Channel Analyzer: Analyze signals in the frequency and time domains
- QSO Digital and Analog Voice: Decode digital and analog voice. Digital voice handled by the built in DSD demodulator, and includes DMR, dPMR and D-Star.
- Beacons: Monitor propagation via amateur radio beacons, and plot them on a map.
We note that the video doesn't show the following additional features such as an analog TV decoder, the SDRAngel "ChirpChat" text mode, a FreeDV decoder and several other features.
A few weeks ago we posted about Reddit member u/OlegKutkov who used his HackRF supercluster to receive Starlink beacons, but details on the HackRF supercluster project itself were a little sparse. Now Oleg has posted a full description about the HackRF supercluster, noting that the 8 HackRF's in the system can provide up to 160 MHz of live monitoring bandwidth.
Oleg shows how each of the boards are connected to the same GPS disciplined 10 MHz clock source, how it uses an RF splitter with LNA and how it requires 8 separate host controllers connected to individual PCIe lines in his computer system to overcome the USB2.0 data bandwidth limits. He also shows the GNU Radio script he's created that combines the 8 sources into one.
Oleg writes how he's using the HackRF supercluster together with a TV Ku-Band LNB and satellite dish for wideband satellite monitoring.
Derek OK9SGC has recently posted a write-up of how they’ve been able to receive the Ku-band beacon signals from the Starlink constellation of communication satellites continually launched by SpaceX since 2015. While we recently covered Starlink Beacons being captured with a HackRF Supercluster Derek has noted that receiving the beacons requires little more than an LNB, a low-cost SDR such as the RTL-SDR V3 and a power injector to provide 12V DC to the LNB. Derek notes that a dish is not even required as the beacons transmit with high power.
Due to the low earth orbit and thus high speed of travel of the Starlink constellation you’ll notice strong Doppler effect drifts in your received signal. Derek notes that it may be interesting to perform Doppler analysis on the satellites with the satellite tracking toolkit for radio observations (strf) software. He also noted that in the 30 minutes he was receiving for, there was almost no point in time where a beacon was not being received, indicating that the Starlink constellation is close to achieving 100% sky coverage.
Derek has made the process easy to understand and illustrates just how easy it is to listen to these beacon signals. Of course we note that these are just the beacons, and they carry no data. Still they are fun signal to receive, and doppler analysis could reveal interesting information about orbits.
Over on Reddit u/Xerbot has posted about the release of his new software called "LeanHRPT". When combined with a software defined radio, this software can be used to decode and view HRPT weather satellite images received from satellites such as NOAA, Meteor, MetOp and FengYun. We note that unlike APT and LRPT weather satellite signals which transmit in the VHF bands, HRPT signals are generally at ~1.70 GHz and require a motorized or hand tracked satellite dish to receive. u/Xerbot writes:
LeanHRPT is a flexible, easy to use and powerful set of tools for the manipulation of HRPT data (maybe I could be convinced to add LRPT support).
When used properly LeanHRPT Decode can generate (almost) L1B data usable in actual land/weather observation, or just pretty images :)
You can get it here: https://github.com/Xerbo/LeanHRPT-Decode
The LeanHRPT project also contains LeanHRPT Demod, as you probably guessed, a HRPT demodulator. It features an incredibly high sensitivity as well as being able to do both realtime (through SoapySDR) and offline demodulation (baseband).
You can get it here: https://github.com/Xerbo/LeanHRPT-Demod