Category: Applications

Using a LimeNET Micro to Implement an Amateur Radio DMR Tier III Trunked Radio Base Station

Thank you to Adrian Musceac (author of QRadioLink) for submitting his article about how he implemented an amateur radio DMR Tier III Trunked Radio Base Station with a LimeNet-Micro software-defined radio. DMR Tier III is a digital voice trunked radio system that employs Time Division Multiple Access (TDMA) technology. Tier III is largely based on Tier II, but adds trunking abilities which enable efficient channel access and resource allocation.

The LimeNET Micro is a software defined radio based on the LimeSDR, but it has some upgraded specifications such as an embedded Raspberry Pi Compute Module 3+ that make it easier to deploy as a base station.

Adrian writes:

The Tier III extension (trunked radio) to the DMR standard is defined and specified by the European Telecommunications Standards Insititute (ETSI) in the TS 102 361-4 document.

The project uses LimeNet-Micro, LimeSDR-mini or Ettus USRP hardware to set up  such a base station for experimental and amateur radio digital voice communications purposes. The core components of this project are MMDVM, MMDVMHost (both under the form of forks supporting communication via ZeroMQ and pseudo-TTY), GNU Radio, DMRGateway, QRadioLink and the DMR trunked radio controller GUI.

Since DMR trunked radio is not very well known and used in the amateur radio world, I hope this will bring some new information to amateurs interested in these digital voice communication technologies. All code used is available as free and open source software (FOSS). A demo of the project used with real world amateur radio communications can be found on the page.

DMR Tier III system software architecture
DMR Tier III system software architecture

Discovery Dish April Manufacturing Update

This was posted over on our Discovery Dish Crowd Supply updates page and we are cross-posting here too.

It’s been over a month since our last update so we thought we’d share some of the recent progress. As mentioned in our last update, during the month of February all manufacturing was shut down due to the Chinese New Year holiday. In early March, staff returned to the factories and began making progress on finishing Discovery Dish.

We have a snazzy new logo, and we are working on obtaining some stickers to include with the feeds.

 

Dish Manufacturing Progress

The molds for the dish stamping machine were successfully created in March and the test stamps have come out great. The manufacturer is still tweaking the secondary mold that stamps the mounting and connecting holes, but we expect that to be completed shortly. Once that is done and tested, we can begin stamping the dish segments en masse.

The Dish mounting system was also finalized and we added 45-degree markers to it, which can help with aligning skew.

We are still awaiting the results of the anodizing tests, but they should be completed by the end of this month. Anodizing the dish is important as the dish must be a dark non-reflective matte color, so that it does not focus hot sunlight onto the feed point plastic head.

Feed Manufacturing Progress

PCB Upgrades

While waiting for the manufacturers to finish up with the molds, we’ve been further refining the PCB feed. Our final version of the PCB has now moved to a PTFE substrate with significantly lower loss at higher frequencies. This has yielded an over 1 dB increase in SNR at the GOES 1.69 MHz frequency.

The change to PTFE was not without problems. An interesting RF engineering problem occurred with the move to PTFE that we wanted to share. When moving to PTFE the only changes to the board layout are PCB trace width changes to keep the impedances matched. Other than that, the boards and layout are essentially identical. However, we discovered that the dual LNA design started oscillating when we moved the PTFE substrate. Oscillations can occur with LNAs when RF essentially bounces back and forth between the two LNAs, which causes undefined behavior in the LNA, such as poor gain, multiple spikes in the spectrum, and unexpected current draw values.

We found this quite odd because oscillations were not occurring in the original FR4 PCB, and the QPL9547 LNA is advertised as ‘unconditionally stable’ which means that it should never oscillate. However, we found that unconditionally stable guarantees may not apply to two-stage designs. In the end, the fix was simple, we just needed to add a damping resistor to one of the inductors on the circuit which reduces its Q-value. It seems that the change from FR4 to PTFE effectively increased the Q-value of this inductor so much, which in turn induced an oscillation in the circuit.

Discovery Dish Feed Head Enclosure

We’ve also refined the entire feed assembly. The feed arm pipe now has a ruler laser etched onto it so that mounting it at the correct distance is easy. A skew angle guide has also been added around the neck. A thumbscrew locking mechanism has been added to the feed head neck too, so that skew can easily be adjusted without the need for a screw driver or Allen wrench to loosen the set screw.

The PCB enclosure has been slightly refined and the injection molding die is currently in production and due to be completed in mid-May. While waiting for the die to be made, we’ve been testing different plastic mixes for the head enclosure to make sure that they are UV stable. The plastic mix has certain strict requirements and choosing the correct mix is crucial. It has to be RF-transparent with a low relative permittivity value, it has to endure direct sun, UV damage, and freezing weather, as well as be water-proof too.

S-Band Feed

Previously as noted in prior updates we were testing an S-band feed with the FR4 substrate. But we found that there was too much loss and the SNR values we got were not great. The move to PTFE substrate means that our experimental S-band feed is now working very well. We will be releasing this in the near future as an additional feed product that can be used with Discovery Dish. This feed will have a frequency range of 2.2 GHz - 2.3 GHz. This covers the main S-band weather satellites, other satellites like Coriolios and JASON as well as the many dump-only S-band satellites that transmit signals only over certain regions.

As requested by most people interested in an S-band feed, the S-band feed will not include a downconverter, so to use it you will either need an SDR like the HackRF which is capable of tuning to the S-band, or a third-party downconverter product.

Discovery Dish Outdoor Metal Enclosure Progress

Our enclosure set is now complete, and the final packing has almost been completed. The user manual can be found here Discovery Dish Outdoor Enclosure User Manual.pdf.

The final set consists of:

  • 1x Metal Enclosure
  • 3x Custom metal cable glands
  • 1x Vent
  • 1x Electronics mounting board
  • 1x Pole mounting set (with hose clamps)
  • 1x Wall/DIN mounting set
  • 1x 10 mm x 10 mm x 8 mm thermal pad (to be placed under the electronics mounting board)
  • 1x 10 mm x 10 mm x 3 mm thermal pad (to be placed under electronics on top of the mounting board)
  • 1x Set of various screws and washers

(Note that there will be some minor changes from this image in sets going out of customers - the hose clamp will be shorter, and the mounting rails will be longer)

Meteor M2-4 Launch

We mentioned in our last update that a new weather satellite Meteor M2-4 was due to launch. The launch was successful and the satellite is now in orbit. The satellite was briefly turned on after launch, and we were able to receive HRPT images from it in the L-band. However, now it is currently in a testing phase so the transmitters are often turned off. We don’t know how much longer it will be in testing, but we assume it won’t be more than a few more months.

GOES-U / GOES-19 Launch Updates

We’ve been keeping an eye on the expected launch date for the next GOES satellite. Currently, it has been delayed from April 30, 2024, to the new date of June 25, 2024, when it will be launched on a Falcon Heavy from Kennedy Space Center, Florida.

Elektro-L4 Updates

In the last update, we mentioned that we were having some problems getting SatDump to receive Elektro L4 properly on computing devices that used ARM processors. After some investigation, we determined that this was a problem with buffer size settings in SatDump and we were able to suggest a fix in https://github.com/SatDump/SatDump/pull/616 which was implemented. New versions of SatDump have this problem fixed.

Driver Tweaks

We have been looking at the RTL-SDR drivers and have found a few tweaks that can improve performance at L-band frequencies. We’ve put a modified version of the librtlsdr/librtlsdr fork up our the rtlsdrblog GitHub at https://github.com/rtlsdrblog/librtlsdr. With this fork and the PTFE feed upgrades, we now get around 5-6 dB of SNR on GOES-18.

Antenna Rotator

The low-cost antenna rotator is finishing up with prototype testing, and we are now working on improving the design’s manufacturability.

Timeline

The ramping of progress from the Chinese New Year holidays to now has been a little slower than expected, but if everything goes perfectly to plan, we will be on time for shipping by the end of June. However, this is currently a best-case scenario. There are still a few manufacturing stages to get through like the final mass production, CE testing and sea freight shipping. Unfortunately, from prior manufacturing experience, there are always setbacks along the way that slow progress, so we are conservatively pushing our advertised timeline back by about 1-2 months. We apologize for any potential delays, but we are working hard to get the product out to you ASAP!

Customer Questions

We have had a few more customer questions over email which we’d like the answer publicly below:

Would it be practical to use this kit indoors to do hydrogen-line astronomy? I ask because I live in a flat in a block of retirement flats, and wouldn’t be able to place an aerial or dish outside, but could find space for a Discovery dish + rotation gear inside.

Unfortunately, indoor Hydrogen line astronomy is out of the question. The hydrogen line signal is just too weak to be seen indoors, and there would most likely be too much interference indoors as well.

What all do i need to purchase and get for the Discovery Dish for Radio Astronomy?

You’ll need these two components from the Discovery Dish Crowd Supply store:

  • Discovery Dish (Dish & Mount Only)
  • Hydrogen Line Discovery Feed

You will also need a software defined radio, such as an RTL-SDR Blog V3/V4 which can be purchased separately, a computer and somewhere to mount your dish (e.g. a mast/tripod etc).

Have you tested this for C-Band / Aero downlink reception?

Currently, we do not have a C-band feed, so we have not tested it for this purpose. Generally, a larger 1.2 m+ dish is required for C-band AERO, so the 70 cm Discovery Dish may not be suitable. We may test this with Discovery Dish in the near future just in case however.

I want to purchase a hydrogen antenna. Where should I buy it? Also, please tell me what is needed to observe seti radio waves.

The Discovery Dish (Dish & Mount) and Hydrogen Line Discovery Feed can be pre-ordered from the Discovery Dish Crowd Supply store. I’m not sure exactly what you are referring to with SETI radio waves. An alien signal could in theory be on any frequency, but the 1.42 GHz Hydrogen line frequency could be a good bet as it’s a universal frequency of interest that any technological civilization would be observing. Realistically the Discovery Dish would be too small to detect potential alien signals unless they were very strong.

I’ve seen a small home made 3D-printed dish called a ‘heliocone dish’ being used for HRPT. How is Discovery Dish different?

The heliocone 3D printer design going around is a great DIY solution for L-Band polar orbiting HRPT satellites. But it has some limitations as it cannot receive the weaker geostationary satellites due to its smaller size and use of a circular polarized feed. It also cannot receive satellites using the opposite circular polarization. It also cannot receive satellites on different frequencies or the Hydrogen Line without designing a new helical feed and using a different LNA+filter combo. Discovery Dish is a more of a general purpose ‘does-it-all’ and ‘ready to use’ out-of-the-box dish. With our dish and feeds you can receive the L-Band polar orbiting HRPT satellites as well as the geostationary satellites. You can quickly swap out the feed for a different feed that covers a different band as well.

 

WarDragon: Testing EMEye/TempestSDR with Wyze Cam Pan V2 Cameras and a USRP B210

Last week we posted about University researchers who found that it was possible to recover live video images from the EM leakage emanating from various IoT security cameras. The 'EMEye' software to do this was released as open-source on GitHub.

Recently Aaron, who created DragonOS and WarDragon, has uploaded a video showing EMEye working on WarDragon. In the video, Aaron shows how to install and use the EMEye software on WarDragon, and demonstrates it working with a Wyze Cam Pan V2 that he purchased for this test.

In this video, I guide you through a practical demonstration of Tempest-based camera eavesdropping attack research. I'll be focusing on the EM Eye project, a tool derived from TempestSDR with some added features.

I'll show you how to construct the EM Eye project, step by step, and how to use it to tune into the EMI emitted by the Wyze Cam Pan v2 using an Ettus B210. By processing this EMI/RF signal, we're able to reconstruct the video stream using the algorithms provided by EM Eye and TempestSDR.

Additionally, I'll demonstrate how DragonOS FocalX and the WarDragon kit offer a cost-effective alternative by including a prebuilt version of TempestSDR that works with the Airspy R2. This allows for similar functionality at a lower cost.

If you're interested we reviewed WarDragon in a recent post as well.

WarDragon EMEye/TempestSDR Camera Eavesdropping Attack Research (B210, Airspy R2, Wzye Cam Pan v2)

The Latest Talks from the Society of Amateur Radio Astronomers

Over on YouTube a bunch of new talks from the Society of Amateur Radio Astronomers (SARA) have recently been uploaded from their recent SARA Western Conference that was held in April 2024. The talks typically involve small home-based radio astronomy setups that use small satellite or WiFi dishes and RTL-SDR or similar low-priced SDRs in their setup. Some of the latest talks include:

  • Nathan Butts: A Novice's Guide to Radio Astronomy (Link)
  • Dr Andrew Thornett: Detecting Cosmic Rays & Building your own version of the Large Hadron Collider (Link)
  • Dr Andrew Thornett M6THO: Lichfield Radio Observatory - Mapping Milky Way at 1420.405 MHz (Hydrogen) (Link)
  • Bruce Randall: IBT Eclipse and other Radio astronomy Failures (Link)
  • Felicia Lin: Mapping the Milky Way by Cross Section Data (Link)
  • Kent Britain WA5VJB: Antennas for Radio Astronomy (Link)
  • Charles Osborne: Eclipse Detection using a VLF Receiver (Link)
  • Rob Lucas - Eclipse Research (Link)
  • Dr Wolfgang Herrmann: Lunar Occultation Observation of Radio Sources (Link)
  • Keynote: Dr Linsay King - Gravitational Lensing (Link)

We note that the last talk was uploaded only a few hours ago at the time of this post, so we're not sure if more talks are yet to be uploaded. So please keep an eye on the SARA YouTube videos page.

Nathan Butts: A Novice's Guide to Radio Astronomy

Testing a WiFi Grid Antenna for L-Band Satellites

Over on YouTube dereksgc has uploaded a video where he tests out a 2.4 GHz WiFi Grid antenna for L-band weather satellite reception. WiFi grid antennas are typically repurposed in the SDR community for L-Band weather satellite reception because they are cheap and mostly work out of the box. They can also be used for hydrogen line radio astronomy. TV dish antennas are an alternative but with them, a custom feed needs to be built. 

In his video, dereksgc tests the WiFi dish on receiving various polar-orbiting L-band satellites including Metop, and Meteor M2. With the polar orbiting satellites the dish needs to point at the satellite as it passes over the sky and so dereksgc recommends using a mount if hand tracking them.

Later in the video he tests some geostationary satellites but finds that the dish is not tuned well enough to receive Elektro-LN3 properly without modifications. He was however able to receive a noisy image from FengYun-2H successfully.

We note that we also currently have our Discovery Dish product available for pre-order, which is similar to the WiFi grid dish, but smaller and lighter weight with a built-in optimized active feed.

I finally got a WiFi grid antenna for satellites

PhantomSDR: WebSDR Software for the RX888 MKII and Other SDRs

Recently Reddit user magicint1337 brought attention in a post to PhantomSDR, a web SDR program for the RX888 MKII SDR. PhantomSDR is not new, having been first uploaded to GitHub two years ago, but it appears that it hasn't gained much attention so far. Web SDR software allows an SDR to be accessed publically or privately remotely over an internet connection. He writes:

PhantomSDR is a Web SDR Software that can sample the whole HF Band using the RX888 MK II, it utilizes the GPU to do so efficiently, the CPU can also be used but has to be strong enough to handle it.

The Software itself supports nearly all Devices, as they are passed from another program like rx_sdr to PhantomSDR. It features high quality Waterfall Zoom efficiently, it can handle hundreds if not thousands of users depending on the Hardware and is open source. There is also a sdr-list linked below.

It's a good alternative to OpenWebRX or WebSDR as it's easy to set up and can handle higher bandwidths and more users than the other alternatives i named. Decoders will also come and run in WebAssembly on the Client, so the Server has no Usage and can handle many Users. It can also handle higher bands, for example VHF.

It is developed further and further because it's open-source and everybody can help develop it further!

List: https://sdr-list.xyz
Software: https://github.com/PhantomSDR/PhantomSDR

The author of PhantomSDR also chimes in on the comments noting:

Author of PhantomSDR here, wondering where all the traffic to the github repo came from and discovered someone has posted it here.

This is started off as project to publish a self-made direct sampling SDR to the internet. Then it grew to became a learning project about SDR and DSP. I picked RX888 as the SDR to put in the screenshot due to it being easily available as compared to the one I built myself. This wasn't really meant to be much apart from a fun learning exercise!

I wanted to open source this because I think others might find it useful also to host higher bandwidth SDRs, or just have a different user interface.

sdr-list.xyz is made by a contributor to the project, but I would prefer to have more infrastructure under the PhantomSDR domain. This will happen once I get a suitable domain name and the server code up. And yes it will be https and the server will be open source.

Currently, there appears to be one publicly hosted server that can be accessed via the list at sdr-list.xyz. 

This web SDR software is reminiscent of the University of Twente WebSDR software which is currently closed source. It is also similar to KiwiSDR and OpenWebRX which is also an online web-based SDR system.

We note that there has been controversy over the RX888 SDR in the past as developers of popular software in the SDR community such as SatDump and SDR++ have frowned on it due to its poor driver support, the lack of any developer support from the manufacturer, and poor overall RF design.

UPDATE: Jie Feng, the author of the software would like to add that the official server list is at https://phantomsdr.github.io/servers. sdr-list.xyz is a third party list set up by a fan, and Jie is working out how to integrate it with his official list. Jie also notes that PhantomSDR also supports many other SDR's like RTL-SDR, HackRF, SDRplay RSP etc. 

Jie has also provided a follow-up Reddit post here

PhantomSDR Screenshot
PhantomSDR Screenshot

Saveitforparts: Receiving and Decoding L-Band Weather Satellites

Over on his YouTube channel 'saveitforparts' has uploaded a new video showing how he has been successful at receiving and decoding L-band weather satellites using his setup made from scavenged parts. He uses a custom-built helical feed on a scavenged dish, and an automatic pan-tilt rotator built from an old security camera mount. With this setup combined with an RTL-SDR and LNA and filter he is able to receive polar orbiting L-band weather satellites. 

In the video, he shows how his system works and what his software setup looks like. He uses SDR++ to record the pass initially, then SatDump to decode the data into images. We note that SatDump can be used to decode the images live, and can also record the raw radio files too, so SDR++ is not required.

How To Receive And Decode L-Band Weather Satellites

Flipper Zero Starts a Petition To Fight Canada Ban

Back in early February we reported about how the Canadian government is making plans to completely ban the Flipper Zero, and popular pentesting tool. The wording from Dominic LeBlanc, Canada's Minister of Public Safety, also implies that software defined radio devices could also be banned.

The reason for the ban is because the Canadian government claims that Flipper Zero and 'consumer hacking devices' are commonly being used as tools for high tech vehicle theft. However, as mentioned in the previous post, this has been debunked.

The team behind Flipper Zero have recently started a petition on change.org to stop the ban. At the time of this post the petition has already reached over 8,000 signature. The team have also penned a comprehensive "Response to the Canadian government" blog post, explaining why the ban makes no sense. In the post they debunk the myth of Flipper Zero being used for car theft, and show the real way high tech car theft is being done.