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.
Over on the usradioguy.com blog, Carl Reinemann has highlighted a very impressive remote off-grid radio satellite image receiver setup by Manuel Lausmann (DO3MLA). The setup consists of two Raspberry Pi's, two RTL-SDRs and a QFH satellite antenna connected to an antenna splitter and bias tee. It is able to receive APT and LRPT images from NOAA and Meteor satellites which transmit at 137 MHz. The received images are then uploaded to the internet via a mobile LTE router.
The system is located a remote part of Northern Norway and is powered by a dual solar and wind turbine system with battery storage. Being so remote with little interference, the system is able to receive very clean images, and with the location being so Northern, it can even glimpse the north pole.
Manuel has uploaded a YouTube video where he shows each part of the system. It is in narrated in German, however the YouTube caption auto translate feature can be used.
He notes that in the future he hopes to install a web SDR like KiwiSDR on the site too.
The SunFounder TS7-Pro 7-Inch Touch Display is a portable high resolution 1024x600 7-inch touch screen with space on the back for a Raspberry Pi 4 to be mounted. It is also possible to mount an optional 2.5" SSD and 'PiPower' battery mount. The price of the TS7-Pro is currently reduced to $79.99 on Amazon and $89.99 in their direct store.
Last year in October we reviewed the 'RasPad 3.0' another SunFounder product that is a portable tablet enclosure for the Raspberry Pi 4. The RasPad is a more complete setup offering a full enclosure and built in battery. We reviewed the RasPad as we were curious to see how easy it would be to integrate a RTL-SDR on the inside. With some minor modifications we were able to successfully do this and create a portable RTL-SDR station. The RasPad 3.0 is a more costly device at US$259 on Amazon and $219 on their direct store.
This year SunFounder reached out to us again and asked if we wanted to test their TS7-Pro display, and see if it is possible to integrate an RTL-SDR.
Unboxing and General Assembly
The TS7-Pro comes packed well with foam. Inside is the manual, acrylic cover, 2x HDMI and 2x USB cables, 2x USB-USB bridge adapter (one for the Pi 4 and one for the Pi 3), 2x Micro-HDMI to HDMI bridge (one for the Pi 4 and one for the Pi 3), various M3 screws, a screwdriver and the LCD screen itself. The cables are designed for people who want to use the screen as a suppletory PC screen, so we did not end up using them.
The rear of the LCD screen contains all the LCD driver circuity as well as speaker and mounting points for the Raspberry Pi to connect it's GPIO header. The required HDMI and USB connections between the Raspberry Pi and LCD screen are handled by small bridge connectors.
The assembly process is very simple. Just mount the Raspberry Pi on the back, connect up the HDMI and USB bridge adapters, and screw on the acrylic backing plate.
There is also a very useful metal kickstand on the back which allows the screen to sit almost upright for easy viewing when placed on a surface.
The acrylic backing plate is designed to be able to mount a 2.5" SSD and/or a 'PiPower' battery module. Instead of using these accessories we decided to see if we could instead fit an RTL-SDR Blog V3 and our own USB battery pack on the back.
The acrylic plate has several screw and venting holes which we made use of to simply zip tie the RTL-SDR onto the back. We then used a short USB extension cable with a right angle connector between the RTL-SDR and Pi 4. There is plenty of space on the inside between the PCB and acrylic plate, so the RTL-SDR can be hidden away with the antenna port still easily accessible.
The USB battery pack is a bit larger, so fits on the outside of the enclosure also via zip ties.
After tightening down the zip ties, and hiding away the excess cabling, the whole construction is stable and not likely to fall apart easily.
Operating and Testing
Both the LCD screen and Pi 4 need to be powered separately. So you will need a battery pack that can support at least two outputs, and one that can support the required power draw of the Raspberry Pi whilst also powering the LCD screen.
We also initially connected a simple whip antenna to the RTL-SDR, but had to change that later as we will discuss.
For software we installed the Pi64 version of DragonOS, which is a ready to use Pi 4 image that has many RTL-SDR compatible programs built into it. A reminder that any software issues we discuss are unrelated to the SunFounder hardware.
The touchscreen works as expected, however we did notice that there is an initial bug on boot where the onscreen keyboard won't work unless you try to log in once with an empty password first. However, as we discovered in the RasPad review, most SDR programs like SDR++ are not very well suited to touch screens, so in the end we ended up connecting a wireless keyboard for ease of use.
Using a keyboard ended up also being a requirement in our tests, because the way we mounted the RTL-SDR meant that the screen was upside down. Using the screen in this 'upside down' orientation was preferred as the kickstand makes it sit a bit more upright and keeps the antenna more vertical. To get around the upside down screen we had to flip the screen in Ubuntu settings. Unfortunately flipping the screen does not also flip the touch screen inputs, so our touch inputs became inversed. There seem to be ways to fix this but we did not look further into the issue.
One other minor annoyance is that we found that the LCD screen would not get recognized by the Pi 4 when the keyboard's USB dongle was connected at boot. This may just be a Pi 4 issue, or an issue with our power pack unable to provide enough current at boot, as we have encountered similar issues in the past with Pi 4's used in other projects. Once the first text appears on the screen, connecting the keyboard USB dongle is possible.
With a keyboard connected, SDR++ opened and ran smoothly, and looks great on the 7 inch screen. We note that we did have to apply a small configuration fix in the Ubuntu sound settings in order to get the built in speakers to work. The fix is the same one used in the RasPad review, so please see that review for more information.
With it's somewhat open back, cooling doesn't seem to be an issue and we never noticed the Pi 4 throttling, or the RTL-SDR overheating.
LCD Screen Interference
Again as we noted in the RasPad review, LCD screens are known to be big sources of RF interference and having the dongle and antenna this close to the screen electronics is not ideal. The image below shows what interference from the LCD screen looks like on the spectrum. Interference on the TS7 screen appears to be more pronounced when compared to the RasPad, possibly due to a different driver PCB with more exposed ribbon cables.
This interference is not present on all bands, and once an external antenna is used with a few meters of coax distance away from the LCD the problem reduces, but it doesn't go away fully. With an antenna disconnected there is almost no interference seen at full gain, so most of the interference appears to come through the coax cable and antenna. So we recommend using high quality shielded coax, as well as getting the antenna away from the LCD screen too.
The SunFounder TS7 Pro is a nice and low cost product that allows you to easily connect a Raspberry Pi 4 to a touchscreen. Unlike the RasPad it does not come with a battery or enclosure, but this allows for a smaller form factor. The LCD screen itself is high quality, bright and with good viewing angles.
Hacking an RTL-SDR and battery pack onto the back of the SunFounder TS7 LCD display is easily possible and does result in a very nice portable form factor. However, there are still wires hanging out the sides which make it a little less neat to carry around and store away, although all the connections seem secure. Mounting the assembly into a 3D printed enclosure could help neaten things up.
LCD interference remains an issue, but by using an external antenna with a few meters of good quality shielded coax the problem can be managed.
Overall we think the product is an excellent starting point for any RTL-SDR Pi 4 project that requires a screen.
Disclaimer: We do not receive any compensation for this review apart from a free TS7 Pro.
Over on YouTube the Society of Amateur Radio Astronomers have recently uploaded talks from their SARA 2022 online conference. Two of the talks we've seen focus on describing results produced by small and cheap WiFi Grid RTL-SDR radio telescopes.
In the SARA conference we've seen two talks expanding on the use of WiFi grids for radio astronomy. In the first talk Alex Pettit discusses how he's used a WiFi grid attached to an equatorial telescope mount, and a custom modified feed in his setup. In his talk he explains how to use the IF average plugin, and how he uses a MATLAB script to process and plot the saved data.
Alex Pettit SARA 2022 Eastern Conference
In the second talk Charles Osborne describes his "Scope-In-A-Box" which consists of the WiFi Grid, LNA, Filter and RTL-SDR combination and compare the setup versus the same hardware used on a larger 3.7m dish.
Charles Osborne SARA 2022 Eastern Conference
If you were interested in those talks, you might also want to check out the other talks from the conference, many of which also involve the use of software defined radios in the receive chain for various amateur radio astronomy experiments.
STD-C is a marine satellite service that broadcasts messages that typically contain text information such as search and rescue (SAR) and coast guard messages as well as news, weather and incident reports. With the right software, an RTL-SDR and an appropriate L-Band satellite antenna like our 'Active L-Band 1525 - 1660 Inmarsat to Iridium Patch Antenna Set' these signals can be received and decoded.
The stdcdec software provides a way for command line only systems to receive and view STD-C data. In his video Aaron shows an example setup that uses SigDigger to determine the audio frequency offset, and receive the audio which is then passed to the stdcdec software. We note that SigDigger is a GUI based program but could probably be replaced with another CLI based program, in order to run on a headless system (as long as the tuning and audio center freq is determined before hand). Aaron is hoping to explore solutions for this in the future.
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.
In a normal setup, weather satellite images from NOAA LEO weather satellites can be received with an RTL-SDR, computing device and an appropriate outdoor mounted antenna that has a good view of the sky. If the antenna is not suited for satellite reception, and/or is mounted indoors, at best only poor quality very noisy images can be received.
The researchers demonstrate that it is possible to combine noisy images received over time, and from different satellites in order to generate a higher quality image. The challenge is that the different satellites and different receiving times will all produce different images, because the satellites will be at a different location in the sky each pass. They note that simply transforming the images in the image domain would not work very well for highly noisy images, so instead they have devised a method to transform the images in the RF domain. The RF signals are then coherently combined before being demodulated into an image.
The results show that 10 noisy satellite images from the indoor system are comparable to one from a comparison outdoor system. However, they note some limitations in that the system assumes unchanging cloud cover during passes. In the future they hope to extend the system to cover other modulation schemes used by other low earth orbit satellites in order to increase the number of usable satellites.
Over the past few years our company has been targeted by counterfeiters who copy our RTL-SDR Blog V3 logos and put it on inferior or old RTL-SDR designs. Up until now determining a fake from an original unit has been possible due to obvious differences in the enclosure.
However, we've now recently seen new counterfeit products appearing on marketplaces with enclosures that look almost exactly like our originals. The counterfeit units copy our logos on the front and back, and text exactly. They also now use rounded enclosures, green PCBs and two screws on the side panels. The only real defining features of the more sophisticated clones are that the side panel screws are not diagonally offset, and that there is no NSY QC sticker on the back noting the batch date.
Again, we want to reiterate that anyone can manufacture and sell RTL-SDRs in general as there is no owner of the RTL-SDR idea itself. However we do have our own specific circuit design and trademarked branding that has become popular over the years due to the features and improvements that we designed and implemented whilst still maintaining a reasonable cost. Other manufacturers/sellers should not trick people into thinking they are ordering an RTL-SDR Blog V3 and they should obviously create their own PCB design and branding.
If you want to ensure that you purchase an original RTL-SDR Blog V3 unit, please use the links on our store page to our official global marketplace listings, or the links to our official local resellers (also on the store page), or order direct from our store if your region is supported. Please note that we cannot provide email support or the two year warranty for counterfeit units.
We are doing our best to enforce our trademark and logos on marketplace sites, but it is a never ending task as once one listing is removed, 10 more appear. If you find that you were tricked by a marketplace listing and received a counterfeit, please be sure to report that store and try to get a refund.
Thanks to all our customers and blog readers for your support over the years! We still have a lot of ideas for new products, tutorials and posts and your support helps us keep this all going!