Tagged: l-band

Turning an old Radiosonde into an Active L-Band Antenna

VK5QI's Radiosonde Collection
VK5QI's Radiosonde Collection

Over on his blog VK5QI has shown how he has was able to re-purpose an old radiosonde into a wideband active L-band antenna. Radiosondes are small packages sent up with weather balloons. They contains weather sensors, GPS and altitude meters and use an antenna and radio transmitter to transmit the telemetry data back down to a ground station. With a simple radio such as an RTL-SDR and the right software, these radiosondes can be tracked and the weather data downloaded in real time. Some hobbyists such as VK5QI go further and actually chase down the weather balloons and radiosondes as they return to earth, collecting the radiosonde as a prize.

VK5QI and his friend Will decided to put some of his radiosonde collection to good use by modifying one of his RS92 radiosondes into a cheap active L-band antenna. They did this by first opening and removing unnecessary components that may interfere such as the main CPU, GPS receiver, 16 MHz oscillator, SAW filters and balun. They left the battery, LDO's, LNA's and Quadrifilar Helix GPS antenna which is tuned to the GPS L-band frequency. Finally they soldered on a coax connector to a tap point on the PCB and it was ready to use.

They then connected the new antenna to a RTL-SDR V3 and fired up GQRX. They write that their results were quite promising with several Inmarsat and Iridium signals being visible in the spectrum. VK5QI also used gr-iridium with the antenna as was able to decode some Iridium signals.

Modified Radiosonde L-Band Antenna connected to a RTL-SDR V3.
Modified Radiosonde L-Band Antenna connected to a RTL-SDR V3.

Airspy HF+ Can Receive L-Band 1.2 GHz to 1.67 GHz

The Airspy HF+ is a much anticipated and recently released software defined radio that specializes in HF and VHF reception. However, one little known and not often advertised feature is that it can actually be used for L-band reception between 1.2 and 1.67 GHz as well. This means that it could be used for signals such as AERO, STD-C, Iridium, the 23cm amateur radio band and more.

Over on YouTube Adam 9A4QV has uploaded a video that tests the HF+ with Alphasat AERO signals at about 1.545 GHz. He notes that the sensitivity is quite good as it is able to receive the satellite signals directly with only the antenna connected and no external LNA used. Of course adding in an external low noise figure LNA and filter would improve the signal even further. Adam notes that reception on the 23cm amateur band (1240 MHz to 1300 MHz) is also quite good with sensitivity reaching about -130 dBm.

Scytale-C: A New Inmarsat STD-C Decoder + Tekmanoid STD-C Decoder Updates

Over on the BitBucket code repository a new open source decoder for Inmarsat STD-C called Scytale-C has been released. The software is available for Windows, and a ready to use binary .exe file can be downloaded from the downloads section of the BitBucket repo.

Inmarsat STD-C is an L-band geosynchronous satellite signal that transmits at 1.541450 GHz. This means that the signal can be received with a simple patch antenna, LNA and RTL-SDR dongle. The satellite is geosynchronous (stationary in the sky), so no tracking is required. On the STD-C channel you'll see messages mainly for mariners at sea such as weather updates, military operational warnings, pirate sightings/reports, submarine activity, search and rescue messages and more. If you are interested we have a tutorial based on other software packages available here which also shows some STD-C message examples. The tutorial can easily be adapted for use with Scytale-C instead.

We've also seen on Twitter that Scytale-C beta tester @otti has noted that a SDR# plugin based on Scytale-C seems to be in the works.

Scytale-C Screenshot
Scytale-C Screenshot

An Important Note on the Coding Ethics of Scytale-C + Tekmanoid Decoder Updates

We feel that it is responsible to make a note on coding and licencing ethics about this software. Originally the software was illegally decompiled by 'microp11' from the closed source Tekmanoid STD-C decoder written by Alex and re-released in a different programming language with a different GUI as the 'open source' B4000Hz software. After Alex took action and micrcop11 realized what he did was wrong he took B4000Hz down. Since then microp11 notes that he has written Scytale-C fully from scratch without the closed source code knowledge. But to be unquestionably legal a full two man clean-room rewrite would probably need to be done as once knowledge of source code is acquired it can be difficult to think of a separate implementation (a somewhat related post discussing this on StackExchange).

However, Alex has noted microp11's passion, and microp11's remorse at the initial decompilation and release of B4000Hz, and has decided to take the higher road and not pursue any further DMCA complaints. Instead he has kindly decided to allow the software to exist, but with acknowledgement of Tekmanoid included. We're glad that the matter was resolved amicably, but still if you use the Scytale-C software we would urge you to still consider the free or paid version of the Tekmanoid STD-C decoder to support Alex

Recently Alex has updated his software to include a spectrum analyzer and more appealing method of displaying EGC messages. Alex writes regarding his Tekmanoid STD-C decoder:

This software [Tekmanoid STD-C Decoder] is closed source and has been since it was first released around 2009. At that time I made a choice to keep the source private but share the executable EGC app for free with the public, so that others could have some fun on the L-band!

The "pro" EGC-LES version was developed in parallel the same year but kept private, nobody even knew it existed. Although I recognized its potential financial value I didn't take "advantage" of it. Firstly because it was a personal hobby project (can't put a price on intellectual property) and second, because I didn't want to help to further expose people's private communications to the open public.

In February 2017 a raw clone of my de-compiled code was made public, to be later withdrawn with an apology. That is the moment I decided to release the PRO version as payware to the public. Many new features present in today's PRO version have been proposed by users and my aim is to satisfy everyone's wishes.

Recently another similar project was released from the same author, with lots of documents to support the code and only minute traces of the initial de-compilation. This time one could indeed claim to have built it "from scratch" - codewise at least. The fact still remains that *part* of the knowledge (not 'code' necessarily) required to put it together was obtained from this initial reverse engineering process.

Despite the negativity surrounding this case, I decided to withdraw my takedown request on the project in exchange for an acknowledgement to the original Tekmanoid decoder, as this person himself wished to include from the start anyway.

To end it with another positive note, I can only hope this newcomer will bring something new to the scene, and that we will see some interesting things!

Below is a video of the updated Tekmanoid decoder.

Update: Microp11 wrote to us after this post went out and wrote the following:

I just want to let you know that scytalec is not a re-write. It is another solution of solving the problem of decoding the Inmarsat-C. Written from scratch. Inadvertently any Inmarsat-C decoder in the 1.5GHz band will have the same the building blocks and they are now documented in detail in the bibliography published with my code. The information is hard to find. All the information is from publicly available sources only. Such that the code will be able to withstand the obstacles or remaining open source. The majority of the documentation is technical manuals, as they each in part reveal a piece of the puzzle, and collectively they contain an almost complete communication protocol. Some are books and they must be the specific revision mention within the bibliography. Moreover if any coder will read the documentation they will actually be able to write a better decoder as I found parts of it too late for a more elegant code writing. And this is the whole idea of scytalec, that anyone can do it if they put their mind to it. There is enough documentation to tackle the C-band as well. And giving enough time, I might be planning on doing that after the sdr# plugin I’m working at. Not alone, as I was and I am being helped by others to which I am grateful and their names were and will be mentioned within the code. Just so you will have an idea of how deep the documentation correctness went for this project, even if a code comment was incorrect, say I was referring to a frame as a “block” or “part” I would get an admonishing email on that. So yes, I have high reasons to stand by this code originality.

Building a 3D Printed LHCP Helical L-Band Feed for Inmarsat, AERO and HRPT

Thanks to Manuel a.k.a. Tysonpower for submitting his latest YouTube video tutorial about building an 1550 MHz L-band LHCP helical antenna for receiving satellite signals such as Inmarsat, AERO and HRPT.

Manuel's design is based on a 3D printed part which is used to accurately form the helical winding. The winding then mounts onto an aluminum plate and a satellite dish arm using a custom 3D printed adapter for the dish arm. In the video he uses the helical feed with an 80cm satellite dish and a standard 40mm LNB mount on the dish arm. Attached to the feed are two LNAs in series which help to lower the noise figure and reduce losses in the coax cable.

With this setup he writes that he was able to get very good AERO and Outernet reception from Alphasat (25E geostationary). He also writes that he's had good results using it for HRPT reception as well.

The 3D printing STL files and list of parts required are available on Thingiverse, and the companion video is shown below. Note that the video is narrated in German, but English subtitles are available.

Manuel's L-Band Helical Feed
Manuel's L-Band Helical Feed

Outernet Dreamcatcher Sale is a Steal: $39 USD RTL-SDR + Computing Board All-In-One

The Outernet Dreamcatcher has recently gone on sale and is now only $39 USD. Previously it was priced at $79 and $59 USD. The Dreamcatcher is an RTL-SDR and computing board all built onto the same PCB. It has two SMA inputs - one is an L-band filtered and amplified input and the other is a standard wideband port good for all frequencies covered by a standard R820T2 RTL-SDR. For $39 it appears that you get the board itself, and a WiFi dongle, but no antennas, cables or SD cards are supplied with the unit.

In you are interested in the Dreamcatcher then back in June we posted a comprehensive review of it as well as their ceramic L-band patch antenna. Since then we've found that the Dreamcatcher has become much more stable and is very useful for applications like setting up a dedicated ADS-B receiver/feeder. At this price the Dreamcatcher is even better value than using a Raspberry Pi 3 plus external RTL-SDR dongle which can end up costing over $60 USD.

According to Outernet stocks appear to be fairly limited so this price probably won't last for too long.

Note: We'd advise not purchasing this for use with the Outernet data signal as we're unsure if that signal is going to last for much longer. Purchase it as a general purpose radio/computer instead.

The Outernet Dreamcatcher Board
The Outernet Dreamcatcher Board

Testing the Prototype Outernet Patch Antenna with Built in RTL-SDR

A few months ago satellite data broadcasting company Outernet created a limited number of prototype receivers that combined an L-band satellite patch antenna, LNA and RTL-SDR into a signal unit. This was never produced in bulk as they found it to be too noisy having the RTL-SDR so close to the antenna, but nevertheless it still worked fairly well.

Over on YouTube max30max31 bought one of these prototype units and made a video about using it for receiving and decoding various L-band satellite signals. In the video he first shows an overview of the product and then shows it receiving and/or decoding some signals like Inmarsat STD-C, AERO and Inmarsat MFSK.

Outernet SDRx Clearance Sale $15: RTL-SDR with built in L-band LNA and Filter

Recently the Outernet project transitioned from using RTL-SDR dongles and C.H.I.P single board computers to using their Dreamcatcher board, which is an RTL-SDR and computing board all in one. In between the transition they also produced a number of ‘SDRx’ dongles. These were custom RTL-SDR dongles with a built in L-band LNA and filter. As they no longer need the SDRx they have them on clearance at their store.

The clearance price is $15 USD which is an excellent deal. Remember though, that the SDRx is limited in frequency range – it is designed for receiving L-band satellites between 1525 – 1559 MHz and the filter will cut off all other frequencies.

The Outernet SDRx on Clearance
The Outernet SDRx on Clearance

Just add a simple L-band tuned antenna to the port and you should be able to receive Inmarsat and a signal like STD-C, AERO or the Outernet signal. A suitable antenna might be a homebrew patch, helix, cooking pot antenna or even a small tuned V-dipole antenna can work for the stronger AERO signals.

We also see that the price of their L-band Outernet active ceramic patch antenna has been dropped down slightly to $25 USD. This antenna is bias tee powered and can be used with a V3 dongle or their Dreamcatcher hardware. The Dreamcatcher itself is also now reduced in price to $59 USD.

We have a review of the Dreamcatcher and active ceramic patch antenna available here.

Outernet Dreamcatcher and L-Band Active Ceramic Patch
Outernet Dreamcatcher and L-Band Active Ceramic Patch

We also now list Outernet products in our store. These are commission sales so we receive a little bit per purchase which supports the blog, and the items are shipped by Outernet within the USA.

If you were unaware, Outernet is a free L-band based satellite service that provides content such as news, weather data, APRS repeats and more. Currently you can get about 20MB of data a day. Outernet receivers are also all based around the RTL-SDR, allowing for very cheap receivers to be built

L-Band and 6GHz Tests with the ADALM-PLUTO SDR

Over on YouTube Adam 9A4QV has uploaded two videos that show his tests with the ADALM-PLUTO SDR on the L-band and up at 6 GHz. In his first video the L-band test shows that the receiver is quite sensitive in this region, managing to receive L-band satellites without any LNA. Although he also tests reception with an LNA4ALL in the receive chain, and this still does improve reception even more.

In the second video Adam confirms that reception is available up to 6 GHz using a PlutoSDR with frequency extension hack enabled.