Many people with an RTL-SDR have had fun receiving NOAA and METEOR low earth orbit (LEO) weather satellite images. However, a step up in difficulty is to try and receive the geostationary orbit (GEO) weather satellites like GOES. These satellites are locked to a fixed position in the sky meaning there is no need to do tracking, however since they are much further away than LEO satellites, they require a 1m+ satellite dish or high gain directional antenna to have a chance at receiving the weak signal. The GOES satellites transmit very nice high resolution full disk images of the earth, as well as lots of other weather data. For more information see this previous post where we showed devnulling’s GOES reception results, and this post where we showed @usa_satcom’s presentation on GOES and other satellites.
The nice thing about Lucas’ post is that he documents his entire journey, including the failures. For example after discovering that he couldn’t find a 1.2m offset satellite dish which was recommended by the experts on #hearsat (starchat), he went with an alternative 1.5m prime focus dish. Then after several failed attempts at using a helix antenna feed, he discovered that his problem was related to poor illumination of the dish, which meant that in effect only a small portion of the dish was actually being utilized by the helix. He then tried a “cantenna”, with a linear feed inside and that worked much better. Lucas also discovered that he was seeing huge amounts of noise from the GSM band at 1800 MHz. Adding a filter solved this problem. For the LNA he uses an LNA4ALL.
To position the antenna Lucas used the Satellite AR app on his phone. This app overlays the position of the satellite on the phone camera making it easy to point the satellite dish correctly. He also notes that to improve performance you should experiment with the linear feeds rotation, and the distance from the dish. His post of full of tips like this which is very useful for those trying to receive GOES for the first time.
In future posts Lucas hopes to show the demodulation and decoding process.
Over on YouTube well known SDR tester Leif (SM5BSZ) has uploaded a video that compares the performance of several HF receivers with two tone tests and real antennas. He compares a Perseus, Airspy + SpyVerter, BladeRF + B200, BladeRF with direct ADC input, Soft66RTL and finally a ham-it-up + RTLSDR. The Perseus is a $900 USD high end HF receiver, whilst the other receivers are more affordable multi purpose SDRs.
If you are interested in only the discussion and results then you can skip to the following points:
24:06 – Two tone test @ 20 kHz. These test for dynamic range. The ranking from best to worst is Perseus, Airspy + SpyVerter, Ham-it-up + RTLSDR, Soft66RTL, BladeRF ADC, BladeRF + B200. The Perseus is shown to be significantly better than all the other radios in terms of dynamic range. However Leif notes that dynamic range on HF is no longer as important as it once was in the past, as 1) the average noise floor is now about 10dB higher due to many modern electronic interferers, and 2) there has been a reduction in the number of very strong transmitters due to reduced interest in HF. Thus even though the Perseus is significantly better, the other receivers are still not useless as dynamic range requirements have reduced by about 20dB overall.
33:30 – Two tone test @ 200 kHz. Now the ranking is Perseus, Airspy + SpyVerter, Soft66RTL, BladeRF+B200, Ham-it-up + RTLSDR, BladeRF ADC.
38:30 – Two tone test @ 1 MHz. The ranking is Perseus, Airspy + SpyVerter, BladeRF + B200, ham-it-up + RTLSDR, Soft66RTL, bladeRF ADC.
50:40 – Real antenna night time SNR test @ 14 MHz. Since the Perseus is know to be the best, here Leif uses it as the reference and compares it against the other receivers. The ranking from best to worst is Airspy + SpyVerter, ham-it-up + RTLSDR, BladeRF B200, Soft66RTL, BladeRF ADC. The top three units have similar performance. Leif notes that the upconverter in the Soft66RTL seems to saturate easily in the presence of strong signals.
1:13:30 – Real antenna SNR ranking for Day and Night tests @ 14 MHz. Again with the Perseus as the reference. Ranking is the same as in 3).
Earlier this month we posted about “cURLy bOi”’s release of his Windows port of telive. Telive is a popular TETRA decoder created by SQ5BPF which until recently only ran on Linux systems. TETRA is a digital voice radio system used in many countries other than the USA.
Now cURLy bOi has just updated his software adding new Windows GUI features and simplifying the install process. The software and text install instructions can be downloaded from his web server, and the code can be found on GitHub.
In order to show the new features and how to use the software cURLy bOi has also created a tutorial video up on YouTube, which is shown below.
The LimeSDR is a RX/TX capable SDR with a 100 kHz – 3.8 GHz frequency range, 12-bit ADC and 61.44 MHz bandwidth. Back in June 2016 they reached their $500,000 goal on the crowdfunding site crowdsupply. They are now gearing up to enter mass production the final product. Recently they released a production update which is quoted below.
Since the successful close of our funding campaign, We’ve been incredibly busy preparing to deliver LimeSDRs to all our backers. Just as we worked hard during the campaign – internally, with key partners, and with our fantastic beta testers in the community — creating a series of exciting demos, we continue to work to ensure backers will have a first-class experience upon receiving their hardware. In this update, we’ll review the state of the production schedule, hardware design, testing setup, documentation, app store, and more.
To be upfront, our production schedule has slipped, but not by a lot. We discovered that some of the parts used in the original LimeSDR design have since entered end-of-life status, so we redesigned the board with replacement parts. In addition, we are still waiting on manufacturers for a few key components, such as the high-precision oscillators. We are in close contact with those manufacturers and our best guess right now is we will have all components by mid-November.
Once we have the components, our manufacturing partner in Taiwan can very quickly produce the entire lot of LimeSDRs. The assembled boards will then be sent to the UK for final quality assurance and packaging before heading off to Crowd Supply’s warehouse for delivery to all backers.
Given all this, we expect all LimeSDRs, including the Aluminum Kit version, to be delivered in December. Of course, we will update everyone as soon as have more information. In any case, we will post an update at least once a week between now and delivery.
Update Your Shipping Address
You will know your order has shipped when you receive a shipping confirmation email from Crowd Supply. The shipping confirmation email will contain a tracking number. If you need to change your shipping address, you can do so by logging into your Crowd Supply account. If you didn’t already have a Crowd Supply account, one was automatically created for you when you placed your order. We will post a separate update letting you know about the cutoff date for updating your shipping address.
Hardware and BoM
We have been contacting all the component suppliers and manufacturers and placing orders through our operation in Taiwan. As part of this work we wanted to make sure that no component will become end-of-life for at least 2 years. As a result, we have had to make minor changes to the board to replace some of the older parts. This was followed by another set of prototype runs to ensure that there is no impact on performance and manufacturability of the boards.
A rigorous testing programme is essential with an advanced technology platform such as the LimeSDR and this work has just been completed. The LMS7002 production test had already been verified and running on industry standard Teradyne testers with RF test configuration. The program for the LimeSDR boards runs on x86-based workstations and provides an optimised test time while exercising all the functions, including frequency and bandwidth sweep across the full range.
Driver and Software Updates
We have already shipped over 100 boards to our community of beta testers for their feedback, before, during, and after the campaign. This enabled us to provide so many truly exciting updates during the campaign and, more significantly, we have been getting excellent feedback from the community, who have been simply outstanding in sharing their ideas for improving the user experience. We are making significant updates to the driver and calibration algorithms as a result, these are largely complete and will be pushed to Github before the end of November.
We will continue to invest heavily in this area and see this as being key to demonstrating our steadfast commitment to the community. Giving you the best support begins with well structured documentation. Obviously, we rely here on your input and feedback. Making the process as smooth as possible is key, we have already started to publish data sheets and supporting documentation on the Myriad-RF Wiki, and will continue to do so as we gather your comments and suggestions.
LimeNET App Store
One of the key activities which we believe will set LimeSDR apart from other software-defined radio solutions is the concept of app-enabled SDR. With this, developers can provide their solution as a incredibly simple to install app, complete with all the various dependencies — with optional support and certification etc. — and publish it via the LimeNET app store. We envisage a rich ecosystem of many applications, resulting in a fantastic out-of-the-box user experience as the maturity and sophistication of the algorithms and software routines improves over time.
We are working very closely with Canonical (the organisation behind the immensely popular Ubuntu Linux distribution) to put in place the app store infrastructure and plan to have a basic service running and populated with a few initial apps by the time the first boards go out.
We are currently in the process of setting out the criteria for publishing an app in the LimeNET store, along with the associated terms and conditions. This is another area where we plan to seek input from you, our backers, to encourage the widest participation and cater for a variety of business and revenue models for developers. There will be numerous posts and updates on this topic, with plenty of opportunity for your input, comments, and feedback.
Last but not least, we shall be posting regular updates as we get closer to the deadline. This will be similar to during the campaign and with plenty of details, including things such as component delivery status, manufacturing progress, and delivery dates for the pledges made by you in all the different categories.
Thank you once again for your support and here’s to the exciting weeks ahead!
Earlier this month Akos from the RTLSDR4Everyone blog reviewed a prototype of the latest ThumbNet N3 RTL-SDR. In this post we will also give a quick review of a prototype of their new unit which was kindly provided to us by ThumbNet. ThumbNet is a company that is hoping to provide low cost satellite deployments, and make use of volunteers around the world with RTL-SDR’s to help track them. The RTL-SDR’s and antenna kits are provided to schools and educational institutions for free by ThumbNet, in exchange for students setting up and monitoring a satellite tracking station.
To help with the needs of their project they have designed and manufactured the ThumbNet N3, which is a redesigned RTL-SDR dongle. As they must order in bulk, they are also selling surplus units to the RTL-SDR community with the hope that any profits will help fundraise for other related projects.
The ThumbNet N3 is a redesigned RTL-SDR with a focus on lowering the noise floor and spurs for optimal reception of their satellites. The N3 uses a 0.5 PPM TCXO for low frequency drift and a common mode USB choke for reduced USB noise. The PCB size is also increased allowing for better thermal dissipation. Since F-type is more common in the areas they intend to donate the units to, an F-type antenna connector is used on the dongle. A full list of the changes and improvements they’ve made can be found on their N3 details page.
One way in which they have reduced the noise is by disabling the internal switching voltage regulator within the dongle, and instead using a linear regulator. Linear regulators are much quieter than their switching counterparts, however they do draw significantly more power. The N3 draws 450mA of current, wheras a standard RTL-SDR draws closer to 270mA. Since many USB ports have a 500 mA limit this gets close to problematic to run directly from the USB port. To get around this, the N3 has an external power port, so it can be powered by an AC->DC power pack (like what you use for charging your phone), or more ideally with a quieter linear power supply or batteries. This has the added advantage of avoiding noisy USB power lines.
Review & Testing
The N3 feels very sturdy, and all the connectors are mounted strongly and are unlikely to break off. The top of the receiver shows the power port, the USB port, the shielding can and the F-type connector. The USB connector uses the older depreciated “USB mini” standard (which is different to USB micro found on most phones).
The bottom shows a few components as well as the two linear regulators. In order to power the unit we used an AC to DC 5V power supply (normally used for mobile phone charging) which we soldered on to the bottom of the PCB. Ideally we’d use a battery or linear power supply, but we’ll test that later with the actual production unit.
The standard N3 unit comes with no enclosure or RFI shielding cans (these are paid add-ons). Our prototype unit came with a shielding can covering the components which was enough to block most interfering signals. We did not see many unwanted signals being received with the antenna unplugged which is a good sign that the shielding can is doing its job.
We gave the unit a quick test on a noise floor scan. The results show that the noise floor has been significantly reduced. The clock spurs are still there but they are reduced in strength vs the standard RTL-SDR.
On L-band at around 1.5 GHz the standard RTL-SDR dongles tend to fail at receiving after they heat up a little. The ThumbNet N3 showed no problems in this region, probably thanks to its larger PCB with better heat dissipation.
Once the production model is released we intend to do a more in depth review, but as it stands right now the N3 is looking very good especially for those who use RTL-SDR’s in monitoring applications that can benefit from very low noise floors, or for those who like the idea of being able to externally power the unit.
The ThumbNet N3 can be bought from their store. It costs $25.75 (with no shielding can), $27.75 (with shielding can), $31.50 (with aluminum case and no shielding can) or $33.50 (with aluminum case and shielding can) + $4.50 worldwide shipping. ThumbNet write that initial demand for the N3 unit has been high, so if you are interested in the unit, you need to order early to ensure that you can get one. They are due to ship out by the end of October. We’ve received a note that the delivery date is rescheduled for no later than November 11.
Also in a recent email from ThumbNet they wrote:
First of all, let me thank you from the whole team, for your support of ThumbNet and helping to promote STEM education around the globe with your purchase. We have sold more of the surplus N3’s than we expected to at this point, so if you have friends that are hesitant, tell them that time is running out!
Secondly, I wanted to take a moment to update you on the status.
The production run testing of the N3 was completed on time, but testing found three small improvements we could put into effect immediately, to produce a better receiver. Those changes have been submitted to the manufacturer and we are currently waiting for a revised ship date.
We still anticipate that the N3 will ship in the month of October, but I will send a follow up email with a more accurate schedule, when I get one in a day or two, from the manufacturer.
I thank you all for your understanding and patience. All of our testing so far indicates that the N3 is performing very well, and we hope you’ll agree it was worth the wait, when it arrives.
Outernet is a satellite based file delivery service. Currently they’re beta testing their service and they are using RTL-SDR’s as the receiver. In previous posts we’ve seen that they’re now regularly transmitting weather updates, wikipedia files and more files like images and books. Over time the service is becoming more and more useful. If you’re interested in receiving their service we have a tutorial available here.
While most of the Outernet software is open sourced, the signal protocol itself is closed source, which ties you into needing to use the official Outernet software. Over on his blog, Daniel Estévez has been working on reverse engineering the Outernet signal with the goal of publishing the results and building a fully open source receiver.
So far he’s managed to fully reverse engineer the modulation, coding and framing. He’s also been able to build a GNU Radio program that receives the Outernet frames and a Python program called free-outernet which does the decoding. His post goes into greater details on how he reverse engineered the signal and what his finding are.
Coherent-receiver.com is a company which is a customer of our RTL-SDR V3 dongle and they have been working on creating a multi-channel coherent receiver product based on the RTL-SDR. An RTL-SDR multi-channel coherent receiver is at its most basic, two or more RTL-SDR dongles (multi-channel) that are running from a single clock source (coherent). A multi-channel coherent receiver allows signal samples from two different antennas to be synchronized against time, allowing for all sorts of interesting applications such as passive radar and direction finding.
The team at coherent-receiver.com have used the new expansion headers on our V3 dongles to create their product. In their receivers they attach a control board which has a buffered 0.1 PPM TCXO (buffered so it can power multiple RTL-SDR’s). They also added an 8-bit register and I2C connection capabilities which allows for control of future add-on boards. The I2C capability is useful because it means that several RTL-SDR dongles can be controlled and tuned from the same control signal. More information on the registers and build of the receiver control board can be seen on their technical support page.
One example application of a multi-channel coherent receiver is passive radar. Coincidentally, we’ve just seen the release of new GUI based Passive Radar software by Dr. Daniel Michał Kamiński in yesterdays post. Passive radar works by listening for strong signals bouncing off airborne objects such as planes and meteors, and performing calculations on the signals being received by two antennas connected to the multi-channel coherent receiver.
A second example is direction finding experiments. By setting up several antennas connected to a multichannel coherent receiver calculations can be made to determine the direction a signal is coming from. An interesting example of direction finding with three coherent RTL-SDRs can be seen in this previous post. A third example application is pulsar detection which we have seen in this previous post.
Coherent-receiver.com sent us a prototype unit that they made with four of our V3 dongles. In testing we found that the unit is solidly built and works perfectly. We tested it together with Dr. Kamiński’s passive radar software and it ran well, however we do not have the correct directional antennas required to actually use it as a passive radar yet. In the future we hope to obtain these antennas and test the coherent receiver and the software further.
Currently they do not have pricing for these models as it seems that they are first trying to gauge interest in the product. If you are interested in purchasing or learning more they suggest sending an email [email protected] It seems that they are also working on additional RTL-SDR ecosystem products such as filters, downconverters, antennas and LNAs.
We hope that the release of this product and Dr. Kamiński’s software will give a boost to the development of coherent multi-channel receivers as we have not seen much development in this area until recently.
Dr. Daniel Michał Kamiński, author of two SDR# plugins has recently released a new passive radar program for the RTL-SDR called “SDRDue”. Passive radar is a technique that makes use of signals from strong distant transmitters. The idea is that these signals can be reflected off the fuselage of aircraft or other flying objects, and the reflection can be observed by a passive radar receiver. By correlating data from two receivers and two antennas, more accurate positional data can be obtained.
For passive radar to work properly the receivers should be coherent, meaning that they run from the same clock and have synchronized samples. The RTL-SDR can be made coherent by connecting two dongles to a single clock source.
The software runs on multi-threaded C# code, and uses Microsoft XNA 4.0 for the graphical operations. It also supports GPU parallel calculations if you have OpenCL and an AMD graphics card.
Please note that we attempted to run the program, but it would not even open on our PC. We’ve contacted the author to ask if there is any known problems. If anyone gets it running please report back in the comments section of this post. EDIT: Daniel has updated the software and it appears to be functioning normally now. You will need to install it into a SDR# folder, and run SDR# first with both dongles before the software will recognise the dongles in SDRDue. We also had better luck with using the rtlsdr.dll_ file, rather than the default rtlsdr.dll file. Just delete the original rtlsdr.dll and rename rtlsdr.dll_ to rtlsdr.dll.
For more information on passive radar we recommend looking at this previous post where we showed the work of Juha Vierinen who used RTL-SDR’s to build a passive radar.