Before this update, to automate the reception and decoding of APT and LRPT satellites a Windows PC, and a huge stack of various decoding and tracking programs and SDR# plugins are required, some of which are now even abandonware.
For APT a typical chain was SDR# -> DDETracker -> Orbitron -> WXtoIMG and for LRPT a typical chain is SDR# -> DDETracker -> Orbitron -> LRPT Demodulator -> LRPT Decoder -> SmoothMeteor -> MeteorGIS. Setting this chain of programs up can obviously be a lot of hard work.
The latest version of SatDump adds automation features which means these two entire chains can be replaced with just one program - SatDump. SatDump is available for Windows, Linux and Mac, so it can even run on something like a Raspberry Pi 5 or Orange Pi 5.
We decided to develop Discovery Dish because we were disappointed by the lack of ready-to-use, low-cost, lightweight dish antennas on the market that are suitable for software-defined radio projects like receiving L-Band geostationary and polar-orbiting weather satellites, as well as for 1.5 GHz Inmarsat reception and 1.42 GHz hydrogen line radio astronomy. With excellent open source weather satellite decoding software, like SatDump, now available, it’s time for a complementary, easy-to-use hardware solution.
Through testing over several years, we chose 65 cm as the diameter, as we found that 60 cm is close to the minimum diameter required for perfect GOES weather satellite reception at 24° elevation, so this size should be suitable for most of the world that has GOES reception available. For LRPT satellites like GK-2A, and HRPT polar-orbiting satellites, it is more than large enough. We combined the dish with a carefully tuned feed that has a built-in low-noise amplifier (LNA) and dual filtering, which means there is no loss from feed to LNA. This also means we can use thinner and less stiff coax cable, which is a lot easier to handle and route. Finally we ensured that the entire dish and feed system is waterproof.
The only other ready-to-use dish offering we found is based on a modified 2.4 GHz grid Wi-Fi dish, which is still in our opinion too big and heavy. Size and weight is especially the important if you want to be able to use a low-cost, light-duty antenna rotator, which typically can only handle less than 1 kg in weight. We found that the grid Wi-Fi dish offering also has no solution for waterproofing the LNA, so the LNA needs to be placed indoors and very thick and unwieldy coax is used to avoid feed to LNA losses.
Other ways to receive these weather satellites and carry out hydrogen line experiments typically involve modifying a 2.4 GHz Wi-Fi grid antenna, or an old satellite TV dish. But these modifications can be time-consuming and difficult to get right, and even 60 cm satellite TV dishes are too heavy for light-duty antenna rotators.
Finally, we developed Discovery Dish with an eye toward it being used with a low-cost antenna rotator, and we are in the process of prototyping our own rotator design. Our antenna rotator is not ready for crowdfunding yet, as there are still some things to work out and long-term stress testing to be done, but please keep an eye out for it in 2024! An antenna rotator is a great addition if you want to use a dish antenna to decode images from the polar-orbiting HRPT weather satellites.
Note that you don’t need an antenna rotator to receive geostationary satellites like GOES, or to do drift hydrogen line observations. For polar-orbiting HRPT satellites, the lightweight nature of Discovery Dish also makes tracking the satellites by hand a much easier prospect.
SatDump is a popular program that is used with RTL-SDRs and other SDRs for decoding transmissions from a wide array of weather satellites and their various imagers and sensors. Recently SatDump's author @aang254 has been working on improving the way projections work. Projections are essentially when the weather satellite image is stretched and skewed to fit correctly over the curved earth.
This means now that city markings and border lines should show up in the correct placed in any images received from SatDump.
If you're interested @aang254 has uploaded blog post on the SatDump website explaining the math, algorithms and problems he found when trying to get projections done right.
In one of his latest YouTube videos, Manuel Lausmann has been testing the RTL-SDR Blog V4 on SDRuno. SDRuno is the official software for SDRplay RSP devices, however, they provide an ExtIO interface which allows it to be used with an SDR that has an ExtIO driver.
In the video Manuel shows how to download and copy over the ExtIO dll, and how to select it in SDRuno. He then goes on to show it in action receiving some HF signals. Note that Manuel's video is narrated in German, but you can use YouTubes auto-caption and auto-translate features to get English subtitles.
In addition to the last Hydrogen Line radio astronomy post from a few minutes ago, we've also recently seen a post on Hackaday about a research paper (PDF) that describes a Hydrogen Line Radio Telescope made from a cooking Wok, LNA and RTL-SDR dongle.
In the paper Leo W.H. Fung et al of Hong Kong University of Science and Technology uses a 61cm cooking Wok with a custom made dipole feed at the calculated focal point. A filtered LNA sits after the feed, and is connected to an RTL-SDR Blog V3 dongle enclosed within a metal cookie box for additional shielding.
The results show that the Hydrogen Line was indeed detected, and measurements of the galactic rotational velocity were possible.
Again we note that we will soon by crowdfunding for a product called the 'Discovery Dish' that will be fairly similar in size and shape. It is designed for receiving L-band weather satellites, but can also be used as a Hydrogen Line telescope too.
In one of his videos from a few days ago Matt from the Tech Minds YouTube channel tests out OpenWebRX+, an unofficial fork of OpenWebRX. OpenWebRX is open source software which enables users to put software defined radios like RTL-SDRs on the internet, allowing people from all over the world to access the receiver if desired, or just letting yourself access it remotely if you want to keep it private.
OpenWebRX+ adds several additional decoders and features on top of the official version. In the video Matt demonstrates OpenWebRX+ running on a Raspberry Pi 4, with an SDRPlay RSPdx. He demonstrates the web GUI in action and shows decoding examples of the various decoders that OpenWebRX+ comes with.
Back in 2020 we released a tutorial about how to use a 2.4 GHz WiFi Grid Dish antenna as a radio telescope which can detect and measure the Hydrogen line emissions in our Milky Way galaxy.
Recently matt from the TechMinds channel has uploaded a video showing this same project but using the NooElec mesh antenna that has been slightly modified for improved performance on 1.7G and 1.4G.
In his video Matt sets up a drift sky scan, where the rotation of the earth drifts the Milky Way through the beamwidth of the dish. Matt uses Stellarium to virtually visualize the live sky map, SDR# and the IF average plugin to average the spectrum, and an Airspy software defined radio.
For the past few years we have been working on finding the best way to help beginners get started with L-band weather satellite reception and basic radio astronomy. We have now come up with a solution that we're calling the 'Discovery Dish' - a lightweight 65 cm diameter dish and active filtered feed set.
Discovery Dish: Simplified system for weather satellite reception and hydrogen line radio astronomy
Discovery Dish is a 65-cm diameter aluminum satellite dish and active filtered feed designed for receiving GOES HRIT, GK-2A LRIT, FengYun LRIT, NOAA HRPT, Metop HRPT, Meteor M2 HRPT and other weather satellites that operate around 1.69 GHz. The dish is designed to weigh under one kilogram, and it splits into three petals, making it easier to ship worldwide. The 1.69 GHz feed contains a built-in LNA right at the feed point, as well as filtering, which means that there is almost no noise figure loss from cables or connectors.
Note that the prototype images show an early non-petalized prototype with rough laser cut wind holes. The production version will obviously be a lot neater looking!
In testing the 65 cm diameter Discovery Dish with it's highly optimized feed has proven effective at receiving the GOES HRIT satellite signal with SatDump. We typically achieve SNR values of 3-4 dB to GOES-18 at 24 deg elevation, and with SatDump an SNR of 1 dB is about the minimum required to receive images so there is plenty of margin. It can also easily receive LRIT from GK-2A and Fengyun, and also when combined with an antenna rotator (or manual hand rotating) can receive HRPT weather satellites too.
The feed on the Discovery Dish consists of a tuned dipole feed with two 5V bias tee powered low noise figure LNAs, and two SAW filters (centered at 1680 MHz with 69 MHz Bandwidth). The feeds are also easily swapped out, and we will also be selling a 1.42 GHz Hydrogen Line feed for those who want to use the dish to get started with radio astronomy. Because the LNA's are right by the feed there is are no losses from feed to LNA, so we can use thinner and easier to handle cabling like RG58 without any loss issues.
In the past we've recommended and relied on 60 x 100 cm WiFi dish antennas for L-Band geosynchronous satellites and Hydrogen Line reception, but at 1.6kg these are too heavy, wide and exert too much torque for light duty antenna rotators to handle. At about half the weight of an equivalent WiFi Dish, the Discovery Dish is much easier to handle.
In the future we hope to be able to provide a low cost light duty antenna rotator that compliments the Discovery Dish. Currently we have tested the Discovery Dish with the AntRunner antenna rotator and found it to be light enough for that rotator to handle, versus a WiFi dish which is far too heavy for it.
Also when compared to a WiFi dish, the Discovery Dish is much easier to optimally set the offset skew as you can simply rotate the feed, versus having to rotate the entire dish at 45 degree increments.
We will also be offering an outdoor electronics enclosure that can be used to house a Raspberry Pi, RTL-SDR and other components like POE splitters. In our tests we have been running an RTL-SDR Blog V4, Orange Pi 5 and POE splitter in the enclosure, and running the SatDump GUI directly on the Orange Pi 5. This results in a neat contained system where only one Ethernet cable needs to be run out to the enclosure.
As we are in pre-launch, pricing is not yet confirmed, but we expect the Discovery Dish to sell for less than US$200 with reasonable worldwide shipping costs. It will be a similar cost to what you would pay if you purchased a WiFi dish, filtered LNA and cabling yourself. Obviously please check what satellites can be seen in your region.
