Over on YouTube the Scanner and Sdr Radio channel has uploaded a video comparing four different brands of HF wideband loop antennas using an SDRplay RSPduo. The loops he tested include the cheap Chinese MLA-30 (~$40), the Cross Country Wireless (CCW) loop ($70), Bonito ML200 (~$442) and the Wellbrook 1530LN (~$305).

The MLA-30 was slightly modified with the cheap coax removed and a BNC connector added. Each of the antennas used a wire loop with diameter of approximately 1.6m, except for the Wellbrook which has a fixed size solid loop of 1m.

The tests compare each loop against the Wellbrook which is used as the reference antenna. In each test he checks each HF band with real signals on the RSPduo and compares SNR between the two antennas.

The results show that the two expensive antennas, the Bonito and Wellbrook, do generally perform the best with the lowest noise floors, but surprisingly the MLA-30 actually performs very well for it's price point, even outperforming the Wellbrook reference on SNR in some bands. We note that some of the improvement may be due to the larger 1.6m loop size used on the MLA-30, compared to the 1m loop on the Wellbrook.

Also we note that it can be hard to compare antennas in single tests, because the differences in antenna radiation patterns could be favorable for some signals, and less so for others, depending on the location.

Thomas from the SWLing blog has been playing around with the recently announced SDRplay RSPdx and has come out with a comprehensive review of the unit. In the review he also provides some comparison videos on real signals between the RSPdx and other SDRs like the WinRadio Excalibur, and Airspy HF+ Discovery.

In the review Thomas notes that while having the advantage of being a wideband receiver, the predecessor to the SDRplay RSPdx (the SDRplay RSP2) was never able to compete with the similarly priced Airspy HF+ and Airspy HF+ Discovery units when it came to HF, MW and LW receiving performance.

But now with it's 0 to 2 MHz enhanced HDR mode activated, Thomas notes that the new RSPdx is majorly improved over the RSP2 in terms of sensitivity and selectivity on the medium wave bands. Thomas' tests also show substantial improvements in the shortwave bands.

Over on YouTube the TechMinds channel has uploaded a new video about decoding Differential GPS (DGPS) using an SDRplay RSPdx SDR. DGPS is a terrestrially transmitted long wave signal that is used to help correct and improve GPS position data calculations which may have timing errors due to atmospheric propagation delays. It works by broadcasting correction data calculated by the difference in received GPS location and the known location of the DGPS transmission site. DGPS is typically transmitted on longwave between 285 kHz and 315 kHz, but in Argentina there are two stations at 2570 and 2950 kHz.

In the video TechMinds explains how DGPS works, and some location around the world from where it is transmitted from. Later in the video he shows a DGPS signal being received by a SDRplay RSPdx SDR, and then show a demo of how it can be decoded with MultiPSK.

We note that there also various other DGPS decoders available including decoders for Android and iOS. A list of decoders can be found on the DGPS sigidwiki page.

One of the selling points of the recently released SDRplay RSPdx is it's special High Dynamic Range (HDR) mode which can be used to improve signal performance for frequencies below 2 MHz. This mode should be especially useful in RF environments where there are strong signals that can overload the SDR and desensitize reception on weaker stations.

Over on YouTube Ivan (aka icholakov) has uploaded a video showing comparisons of signals being received with HDR mode turned on and off. He tests it on weak NDB DX signals, and on medium wave broadcast AM. The results do appear to show that using HDR mode results in an improvement in signal strength.

Over on the SWLing post blog we've seen a post contributed by Mike Ladd who works with SDRplay. Mike has been comparing the new SDRplay RSPdx on medium wave and long wave reception against the Elad FDM-S2, Airspy HF+ Discovery and the Perseus. The RSPdx is SDRplay's latest product which sits at the top of their line as their highest performance single tuner receiver.

Each test consists of a video where he runs a comparison between the RSPdx and another receiver. All SDRs are run in SDRuno, the official application for SDRplay receivers. It is left for the listener to determine which SDR sounds better. From a listeners perspective, it appears that the RSPdx performs at least identically to the other SDRs.

SDRplay have recently released an update regarding third party software support and availability of their latest RSPdx receiver. They write:

Happy new Year from all of us at SDRplay.

Here’s an update on additional software for the RSPdx. SDRplay’s SDRuno fully supports the RSPdx but it takes several weeks for other software to catch up to the capabilities offered on the other RSP models.

Simon Brown has released his latest version of SDR Console V3 which supports the RSPdx (Version 3.0.18 dated January 1st) over on https://www.sdr-radio.com/ (make sure you download the latest API 3.x from our downloads page first)

We have released an EXTIO plugin for the RSPdx which will enable the RSPdx to work with any EXTIO-based software (e.g. HDSDR) although it doesn’t support HDR mode. HDR mode will not be added and the source code for the plugin can be found on our GitHub repository (https://github.com/SDRplay/ExtIO_SDRplay) we will not be supporting the plugin source code or extending the plugins capabilities. They are all free to be modified.

It is important to note that the RSPdx ExtIO plugin does NOT, AND WILL NOT, support HDR mode. If you need HDR mode, then SDRuno is the best option. HDR mode requires the end application to work in a certain way and this is not something that can be controlled via the ExtIO protocol.

Work has also begun on supporting RSPdx for SoapySDR based applications such as Cubic SDR (again this won’t include HDR mode). A Gnu Radio source block for the RSPdx will follow.

We are working with Steve Andrew, author of the Software Analyser software programme (see https://www.sdrplay.com/spectrum-analyser/ ) to help get compatibility for the RSPdx – this is a slightly longer process so this will take several more weeks.

Regarding stocks of the RSPs, SDRplay and most of our resellers on www.sdrplay.com/distributors/ have plenty of stock of RSP1A and the RSPduo. However there continues to be a shortage of the RSPdx whereby many of the resellers have sold out of their first deliveries. SDRplay is queuing up their replacement orders on a first come, first served basis. We also have our own quantity planned in there to allow us to sell direct from our website. We still hope that by the end of January we will have supplied this second wave of RSPdx demand.

Over on YouTube TechMinds has uploaded a new video explaining NavTex and showing how to decode it with an HF capable SDR like the SDRplay RSPDx. NavTex is a marine digital data radio service designed for transmitting information like navigational and meteorological warnings, weather forecasts and maritime safety information. It is broadcast in either the MW frequency band at 490 kHz and 518 kHz or in the HF band at 4209.5 kHz.

In the video TechMinds uses a guide put out by Mike Ladd from SDRplay (pdf warning). The guide explains how to connect SDRuno to a NavTex decoder called YanD via a virtual audio cable. The rest of the video shows a NavTex message being decoded, some sample messages, and a closer look at YanD. 

Even if you don't use an SDRplay, the guide could be adapted for other SDRs too.

Over on his YouTube channel TechMinds has uploaded a video reviewing the X1-HF 1 - 50 MHz Trapped Coil Receiving antenna from Moonraker.eu which goes for £69.95. This is a small electrically short antenna for HF reception which is easy to setup and install, requiring no radials. However, like all short HF antennas it is a compromise.

In the review he uses an SDRplay RSP2 SDR to test HF reception with the antenna. Later in the video he also tests it outside the advertised 1 - 50 MHz range. He concludes that the antenna works very well for it's small size.

SDRplay have recently released an update on how the Coronavirus is impacting their supply lines. In short, they note that their fulfillment is currently normal, but there may be delays in the logistics distribution network. In terms of stock levels, they have enough to cover a few more weeks of normal buying, but beyond that the supply chain is not certain and there may be restocking delays.

Dear customer,

We have been fortunate that our suppliers have been able to source the components needed to fulfil our current backlog commitments. In particular the demand for the new RSPdx exceeded our expectations, and that has caused shortages up until now.

However we now have enough product available to continue supply of all three SDRplay production RSPs for a few more weeks at traditional buying levels. Beyond that, we will be dependent on our subcontract manufacturing partners’ ability to source components. As the coronavirus situation unfolds it is likely that restocking will take significantly longer than usual and we are working with both suppliers and our distributors to do our best to plan for the uncertain future.

Meanwhile, regarding orders placed in the next week or so, SDRplay and its fulfilment centres are currently working as normal, BUT please be aware that logistical delays in the distribution network are likely – so please be patient if your shipment takes longer than expected.

We’d also like to take the opportunity to send our best wishes to all our customers and their friends and families as this emergency situation develops.

Jon, on behalf of the SDRplay team.

Librespace, who are the people behind the open hardware/source SatNOGS satellite ground station project have recently released a comprehensive paper (pdf) that compares multiple software defined radios available on the market in a realistic laboratory based signal environment. The testing was performed by Alexandru Csete (@csete) who is the programmer behind GQRX and Gpredict and Sheila Christiansen (@astro_sheila) who is a Space Systems Engineer at Alexandru's company AC Satcom. Their goal was to evaluate multiple SDRs for use in SatNOGS ground stations and other satellite receiving applications. 

The SDRs tested include the RTL-SDR Blog V3, Airspy Mini, SDRplay RSPduo, LimeSDR Mini, BladeRF 2.0 Micro, Ettus USRP B210 and the PlutoSDR. In their tests they measure the noise figure, dynamic range, RX/TX spectral purity, TX power output and transmitter modulation error ratio of each SDR in various satellite bands from VHF to C-band.

The paper is an excellent read, however the results are summarized below. In terms of noise figure, the SDRplay RSPduo with it's built in LNA performed the best, with all other SDRs apart from the LimeSDR being similar. The LimeSDR had the worst noise figure by a large margin.

In terms of dynamic range, the graphs below show the maximum input power of a blocking signal that the receivers can tolerate vs. different noise figures at 437 MHz. They write that this gives a good indication of which devices have the highest dynamic range at any given noise figure. The results show that when the blocking signal is at the smallest 5 kHz spacing the RSPduo has poorest dynamic range by a significant margin, but improves significantly at the 100 kHz and 1 MHz spacings. The other SDRs all varied in performance between the different blocking signal separation spacings.

Overall the PlutoSDR seems to perform quite well, with the LimeSDR performing rather poorly in most tests among other problems like the NF being sensitive to touching the enclosure, and the matching network suspected as being broken on both their test units. The owner of Airspy noted that performance may look poor in these tests as the testers used non-optimized Linux drivers, instead of the optimized Windows drivers and software, so there is no oversampling, HDR or IF Filtering enabled. The RSPduo performs very well in most tests, but very poorly in the 5 kHz spacing test.

The rest of the paper covers the TX parameters, and we highly recommend going through and comparing the individual result graphs from each SDR test if you want more information and results from tests at different frequencies. The code and recorded data can also be found on the projects Gitlab page at https://gitlab.com/librespacefoundation/sdrmakerspace/sdreval.

Over on YouTube TechMinds has uploaded a video where he explores the QT-DAB software (formerly known as SDR-J), which is a program capable of decoding Digital Audio Broadcast (DAB) signals. QT-DAB is compatible with several SDRs including the RTL-SDR, HackRF, Airspy and SDRplay units. 

DAB stands for Digital Audio Broadcast and is a digital broadcast radio signal that is available in many countries outside of the USA. The digital signal encodes several radio stations, and it is considered a modern alternative or future replacement for standard analog broadcast FM.

In the video TechMinds explains how to download, install and use the software on a Windows machine. He goes on to demonstrate some DAB decoding in action with various SDRs and then shows how to connect QT-DAB to a remote RTL-SDR via rtl_tcp.

Over on YouTube user Tech Minds has uploaded a video showing how you can determine if you are getting HF interference from a VDSL internet connection going to your house or neighbors. VDSL or Very High Speed Digital Subscriber Line is an internet connection technology that runs over old copper phone wires allowing for a fast broadband connection. The frequencies used by VDSL are between 25 kHz to 12 MHz, and for VDSL2 up to 30 MHz. Unfortunately the frequencies used can result in high amounts of radio interference from RFI radiating from the copper phone lines which is a major problem for HF amateurs and short wave listeners.

In his video Tech Minds uses an SDRplay RSPdx to record a short IQ file of the VDSL interference that he experiences in his home in the UK. He then opens the IQ file in a piece of software called Lelantos, which was developed by a member of the UK amateur radio organization RSGB. If a VDSL signal is present, this tool will determine various bits of information about the interference, and will give you enough information to make a complaint to OFCOM, the UK's radio communications regulator.

Earlier in the month SDRplay released SDRuno V1.4 RC1. This is a beta version that amongst other changes now has the capability to run "plugins". Plugins allow developers to easily create modules that extend the functionality of the SDRUno software. For example right now there is a plugin included with V1.4 RC1 that allows users to listen to DAB audio. Up until recently plugin functionality has only been available in Airspy's SDR# software, so it's good to see SDRuno finally including this feature too.

Over on the Techminds YouTube channel Matthew has uploaded a short video where he tests out the new plugins feature. First he tests out the DAB decoder, noting that the CoreAAC codec needs to be installed first separately. Later he tests the second plugin which is an audio recorder that allows users to record audio to MP3.

In a recent YouTube video Tech Minds shows how to decode GMDSS (Global Maritime Distress and Safety System) messages which are broadcast on MW and HF. In the video he explains the DSC (Digital Selective Calling) which allows calls to be made to individual ships, a group or all stations. He goes on to demonstrate the YADD GMDSS DSC decoder running via the HF audio piped in from SDRUno and received with an SDRPlay RSPdx.

Our metal case upgrade kit for the SDRplay RSP1A software defined radio is now back in stock in our store and will be ready to ship out within the next couple of days. This is a premium aluminum metal upgrade enclosure for the SDRplay RSP1A. Helps block RF interference and protects the RSP inside the sturdy enclosure. This will be the final batch made of this product, so if you are interested please order before stock runs out for good.

The kit includes 1x black aluminum metal enclosure with two labelled side panels, 1x black semi-hardshell carry case, 1x thermal pad to keep the RSP1A cool and mechanically stable inside the enclosure, 1x accessory set including enclosure screws, GND lug bolt set and 3M anti-slip rubber feet.

In his latest YouTube video Tech Minds shows how to decode HF ACARS (HFDL) with an SDRplay RSPdx. Tech Minds initially explains what HFDL is, and how it is typically received via special aviation radios. He goes on to show how we can decode it from home with any HF capable SDR, and a program called PC-HFDL. Finally he explains how to set up a Google Earth file that can display the aircraft location data that is provided in some HFDL messages.

Back in April we posted a video from Tech Minds where he showed us how to use special software combined with an SDRplay RSPdx to detect and report VDSL interference on the HF bands. VDSL or Very High Speed Digital Subscriber Line is an internet connection technology that runs over old copper phone wires allowing for a fast broadband connection. The frequencies used by VDSL are between 25 kHz to 12 MHz, and for VDSL2 up to 30 MHz. Unfortunately the frequencies used can result in high amounts of radio interference from RFI radiating from the copper phone lines which is a major problem for HF amateurs and short wave listeners.

Recently John Rogers (M0JAV) presented a talk via the UK amateur radio organization RSGB. In the talk he explains how VDSL works, why it causes RFI and how to check for VDSL RFI using an SDR and the Lelantos software. He also shows how he drove around with a magnetic loop antenna looking for VDSL RFI sources in his neighbourhood. He then goes on to call out for more volunteers in the UK to submit RFI reports to Ofcom as they responded that they won't do anything about the interference unless there are more complaints. 

The RSGB EMC Committee (EMCC) has been investigating VDSL interference since 2014. As the number of installations has risen to over 30M the interference level at amateur radio stations has also increased. The majority of radio amateurs are now impacted by this problem.

In the May 2020 RadCom we outlined how to detect and estimate the level of interference. This can be done by inspection of an SDR spectrum display or by taking a recording and then using a SW package—developed by Martin Sach of the EMCC—which identifies the VDSL signature in the recording and shows how many different VDSL lines are causing the problem and what their relative strengths are.

This talk demonstrates what to look for and how to use the tools to find out if you have a problem yourselves. We hope this will help you respond to our call for action and complain to Ofcom about the level of RFI you are subjected to.

John Rogers, M0JAV
Chair EMCC

Over on the SDRplay blog Jon has posted about the STRATONAV experiment which makes use of the SDRplay RSP1 software defined radio. The STRATONAV experiment uses high altitude balloons to carry the RSP1 as well and a commercial portable receiver. The two receivers were configured to receive aircraft VOR navigation signals in order to test the effectiveness of VOR when used at extreme altitudes of up to 28 km. The VOR navigational data was then compared against GPS tracks, resulting in a measure of how well VOR worked at those altitudes. 

VOR (aka VHF Omnidirectional Range) is a navigational beacon that is transmitted between 108 MHz and 117.95 MHz from a site usually at an airport. In the past we have posted about VOR a few times as it can also be decoded with an RTL-SDR, or used for passive doppler aircraft radar. 

The results showed that VOR navigation does indeed continue to function at extreme altitudes, proving that it can be used as a back up navigation system for stratospheric platforms. They also note that VOR navigation could also be used as a primary navigation system on smaller stratospheric platforms due to its low cost and low complexity to implement.

The full academic paper is available on sciencedirect, or for free via Sci-Hub.

SDRplay have announced the start of their undergraduate University course titled "Understanding Radio Communications". This course is created by the Sapienza University of Rome and consists of text material plus a series of YouTube videos released on the "SDRplay Educators" channel. Currently only the introduction videos are released, and they note that all videos will be released in early December 2020. A PDF info sheet about the course can found here, and if you wish to register for the course you'll need to sign up at sdrplay.com/understandingradio.

The course appears to be intended for University teachers in order to accelerate adoption of SDR based teaching of RF courses. We're unsure if this material will be released to the general public as their signup form appears to ask for University details. They write:

Alton, England; 5th November 2020 – SDRplay Limited announces a new Radio Communications course for under-graduate teaching as part of its SDRplay Educators Programme

“Understanding Radio Communications – using SDRs” includes a rich set of teaching materials and practical exercises to help students understand the key elements of radio communications. This one semester course provides teaching materials and practical workshops that lead students from the first switch-on of a Software Defined Radio (SDR), through to signal reception, demodulation, and finally, successful communications with satellite signals.

As well as guides and set-up instructions for teachers for both the lecture and lab sessions, there are downloadable teaching materials in both PowerPoint and .pdf formats. There are video guides showing the lab activities and there’s a dedicated new forum for teachers to share experiences and to get help from the authors.

The course was created in association with academic partners Sapienza University of Rome, Department of Mechanical and Aerospace Engineering whose intention was to create a practical course that will inspire Science, Technology and Engineering students to nurture their understanding of radio communications.

The course started life as a 12-hour optional course for third-year bachelor students in Aerospace Engineering and has been broadened to make it suitable for all students that have some basic knowledge of signal theory and signal processing. It can either be run as an additional or optional “module” or adapted to be included as materials within a full year radio communications subject.

Robert Owen, University Programme specialist at Essaimage who guided the academic team, says, “I have spent 26 years in global “University Programmes” and across this time I’ve learned two fundamental principles. The first is that teaching materials must fill an essential need in the curriculum, not just be something that business thinks should be taught. And secondly, that the best teaching materials come from academics not commercial trainers. This course, Understanding Radio Communications, fulfils these principles generously, and I am proud to be associated with it!”

The details of the course structure can be found by going to https://www.sdrplay.com/understandingradio/

Key dates:19th November 2020, 1300 UTC – SDRplay and Course developers, Lorenzo Frezza and Paolo Marzioli from the Department of Mechanical and Aerospace Engineering, (DIMA), Sapienza University of Rome, will host a webinar presenting the programme and taking questions via YouTube chat.

About the SDRplay Educators Program The SDRplay Educators Program provides practical encouragement to teachers around the world so that they can use SDRplay’s SDR receivers in courses and student projects. The focus is on providing the key elements needed to teach a course: a suitable hardware platform at a reasonable price, ready access to SDRplay software, effective technical support, and excellent teaching materials that serve genuine teaching needs. The SDRplay Educators Programme is open to all members of academia, see

https://www.sdrplay.com/educators/

In this week's Tech Minds video Matthew interviews the SDRplay team and also takes a tour of their design lab and PCB manufacturing facility. SDRplay is a manufacturer of low cost wideband software defined radios, with the cheapest starting at US$109.

The video starts with an interview with Jon Hudson from the SDRplay sales team who gives an overview of the entire SDRplay product line up, also explaining how the products have been iterated on over time. Jon also talks about the SDRuno software and team members in the company.

The next interview is with Andy Carpenter who is the head of SDRplay software development. Andy talks about SDRuno and how it came to be acquired and improved by SDRplay. They go on to discuss some recently added SDRuno features such as the plugin environment as well as the upcoming feature roadmap.

The final part of the video is a tour of the equipment used at the SDRplay design lab, and a tour of the UK based PCB manufacturing facility contracted by SDRplay.