Over on the Thought Emporium YouTube channel the team have uploaded two videos that may be of interest to radio hobbyists. The first video shows a nice overview about receiving NOAA weather satellite images. They explain everything from scratch for complete novice, so the videos are great for almost anyone to watch and learn about radio and SDR concepts. The blurb of the first video reads:
Over the past 2 months, me and my friend Artem have been building antennas to receive signals from weather satellites as they pass overhead. This video chronicles our progress through this project and goes through some of the science involved in working with radio and receiving transmissions. We explore how dipoles work and how to build them, and how we built our final double cross antenna. We used an SDR (software defined radio) called a HackRF to do the work of interpreting the received signals and then decoded them with some special software. We pulled images from 4 satellites: NOAA 15, 18 and 19 as well as METEOR M2. The satellites broadcast immediately as they take the images and no images are stored, so we’re likely the only ones on earth with these images.
The second video is about building a radio telescope. Like the NOAA video, they explain all concepts in a simple and easy to understand way, so that anyone even without any radio knowledge can understand what the project is about. In the video they also show how they use a 3D printer to create a tracking mount which can point a satellite dish. They then use the dish to create a satellite heat map. The blurb reads:
Over the last 2 months me and my friend Artem (you met him in the last video) built our first radio telescope. It was built mostly out of off the shelf components, like a satellite dish and Ku band LNB, as well as some parts we 3d printed. When all was said and done we had a system that could not only take images of the sky in radio frequencies (in this case 10-12ghz), but could also be used to track satellites. With it, we were able to see the ring of satellites in geosynchronous orbit, over 35,000km away, This is only the first of what I suspect will be many more telescopes like this. Next time we’ll be building ones that are far larger and can see things like the hydrogen lines so we can image the milky way.
Over on his blog Adam 9A4QV (seller of various RTL-SDR related goods including the LNA4ALL) has just made a post detailing a build of a high performance super simple NOAA/Meteor M2 weather satellite antenna. Most antenna designs for polar orbiting weather spacecraft are based on circularly polarized turnstile or QFH designs. However, Adams antenna is based on a very simple linearly polarized dipole, which makes construction almost trivial.
The idea is that by arranging a dipole into a horizontal ‘V’ shape, the radiation pattern will be directed skywards in a figure 0 (zero) pattern. This will be optimal for satellites travelling in front, above and behind the antenna. Since polar orbiting satellites always travel North to South or vice versa, we can take advantage of this fact simply by orienting the antenna North/South.
There is also another advantage to Adams design. Since the antenna is horizontally polarized, all vertically polarized terrestrial signals will be reduced by 20 dB. Most terrestrial signals are broadcast in vertical polarization, so this can help significantly reduce interference and overloading on your RTL-SDR. Overloading is a big problem for many trying to receive weather satellites as they transmit at 137 MHz, which is close to the very powerful FM broadcast band, air band, pagers and business radio. In contrast a circularly polarized antenna like a QFH or turnstile only reduces vertically polarized terrestrial signals by 3 dB.
As the satellites broadcast in circular polarization there will be a 3 dB loss in Adams design from using a linear polarized antenna. But this can be considered as almost negligible. Adam also argues that the home construction of a QFH can never be perfect, so there will always be at least a ~1dB loss from inaccurate construction of these antennas anyway.
The final advantage to Adams design is that construction is extremely simple. Just connect one element to the center coax conductor, and the other to the shield, and spread apart by 120 degrees.
Adam has tested the antenna and has gotten excellent results. If you want more information about the antenna design, Adam has also uploaded a pdf with a more indepth description of the design and his thoughts.
Over on his blog author Manuel a.k.a ‘Tysonpower’ has written about a DIY Carbon Fibre Yagi antenna that he’s built for only 20€. The antenna is very lightweight thanks to a 12mm diameter carbon fibre pipe which is used as the main boom. It also uses 3D printed parts that clamp onto the carbon fibre pipe and hold the metal elements in place. The advantage of the carbon fibre pipe over a PVC one is not only is it lightweight and much easier to hold, but it also stronger, and much less bendy and floppy. The metal elements are welding rods which he found on eBay, and the carbon fibre pipe was sourced cheaply from China with Aliexpress.
A Yagi is a directional antenna with high gain towards the direction it is pointing. You’ll need to hand point the Yagi in the general direction of the satellite as it passes over, but you can expect much higher SNR readings compared to something like a QFH or Turnstile.
Manuel designed his antenna for 2M satellites (NOAA, Meteor M2, ISS etc), and was able to achieve over 36 dB SNR with an RTL-SDR.com V3 receiver, FM Trap and LNA4ALL on NOAA 18 at a 34° max. pass. He writes that the design is easily modifiable for other frequencies too.
To show off the design, construction and performance of his antenna he’s uploaded two videos to YouTube which we show below. The speech is in German, but even for non-German speakers the video is easily followed
Over on YouTube Adam 9A4QV has uploaded a video showing how to build a DIY bandpass filter for 137 MHz. This can help improve the reception of NOAA and Meteor M weather satellites, by blocking strong out of band signals. Adams design is a 132 MHz – 142 MHz Butterworth bandpass filter which gives about 35 dB attenuation outside of the pass band. He’s also posted a write up documenting the filter design on his website.
Lucas Teske recently went ahead and built the 137 MHz filter suggested by Adam. Lucas didn’t have the correct capacitor values so he ended up cascading several in series. His results showed that the filter did improve his reception significantly.
A few days ago we reported that the Outernet L-band satellite service had just upgraded their software to make it available for receiving APRS and weather updates. Back then it wasn’t clear what the weather updates would entail. Today weather updates starting being transmitted. They are using NOAA data and displaying it on a live weather app (which can also be viewed online here).
The app can be used to view weather data such as wind vectors, temperatures, relative humidity, total precipitable water, total cloud water, mean sea level pressure and ocean currents. Outernet writes that the global weather data will be updated via their satellite system once per day, and that each update also provides 24h, 48h and 72h predictions.
We also see that grib files for mariners are now coming in as well as several Wikipedia articles and regular APRS broadcasts from the ISS.
It looks like the Outernet service is becoming more and more useful over time. If you are interested in receiving Outernet with an RTL-SDR see our tutorial post here.
Over on Reddit user merg_flerg has uploaded an imgur post that carefully details a step by step guide for building a double cross antenna. A double cross antenna is great for reception of satellites like NOAA and Meteor since it has a sky oriented radiation pattern with very few nulls. This means that it can receive satellite signals coming from the sky well. Alternative antennas for NOAA/Meteor include turnstiles and QFH antennas, although the double cross antenna seems to have the least nulls, meaning that the signal is less likely to fade in and out as the satellite moves across the sky.
merg_flerg’s design is also modified from the standard design slightly, allowing it to become easily disassembled and carried within a backpack. At the end of his tutorial he writes that he gets much better reception with his double cross antenna than he does with his QFH.
In the post he demonstrates the final constructed antenna decoding a NOAA APT weather satellite image with an RTL-SDR and the WXtoIMG software. See our tutorial for information on decoding NOAA weather satellite images.
It is well known that the NOAA satellites broadcast weather satellite images which can be received and displayed with an RTL-SDR and computer. What is less known is that there is a telemetry beacon that is also transmitted by the same satellites. The telemetry not only contains data such as the current spacecraft time, day and ID, but also contains scientific data from on board instruments such as:
The HIRS/3 and HIRS/4 instruments which is a high resolution infrared sounder which can be used to create a low resolution multi-spectral scan of the earth. (more info)
The Space Environment Monitor (SEM-2) which has a Medium Energy Proton and Electron Detector (MEPED), and a Total Energy Detector (TED). This experiment is used to measure the effect of the sun on satellite communications. (more info)
The experimental DCS/2 transmitter which retransmits signals from 401.65 MHz sea buoys, arctic fox collars, sea ice monitors, weather balloons and more. (more info pdf)
The ARGOS Advanced Data Collection System (ADCS) which amongst other uses is used in research for tracking animal GPS collars around the world.
According to various reports the Russian Meteor M-N2 satellite appears to be active again once more. The Meteor M N-2 is a polar orbiting Russian weather satellite that was launched in July 2014. It transmits with the LRPT protocol which allows us to receive weather satellite images with an RTL-SDR that are of a much higher resolution than the NOAA APT satellites.
Unfortunately late last year Meteor M N-2 had some problems and LRPT transmissions were turned off for the time being. During this downtime the Russian space agency switched the LRPT transmitter on the older Meteor M N-1 satellite back on, even though the satellite was tumbling in orbit. Currently people are not reporting any signal from Meteor M N-1, so this may have been turned off, perhaps temporarily.
Now however, it seems that Meteor M N-2 has been switched back on again and various people have already successfully received its signal. If you want to receive these Meteor M N-2 weather images with an RTL-SDR dongle or other SDR then you can view the tutorial written by Happysat here.