Cloud-SDR is a company that aims to make using SDR over the cloud/network/internet easier. It allows you to set up a remote SDR server that you can access from anywhere. Previously Cloud-SDR was still in development, but now we recently received mail from Cloud-SDR programmer Sylvain that the client and server software has just been released for the RTL-SDR. It appears that it also currently supports the Airspy, BladeRF, SDRplay and PerseusSDR.
The email reads:
I am pleased to inform you that we have just released two softwares compatible with your devices :
The Cloud-SDR free client, a windows + Linux (to be released soon) client able to run locally RTL-SDR devices (check the news/turorials, we have featured several times dongles from your blog)
The Cloud-SDR streaming server (codenamed SDRNode) , a windows + Linux (to be released soon) multi-user configurable streaming server.
SDRNode is a commercial software but an evaluation version is already available. Both softwares can be downloaded from our store after registration.
Source code for the drivers are already released as open source software through our GitHub repo: https://github.com/cloud-sdr
To download the software you must register an account with them at https://store.cloud-sdr.com/my-account. The client is free but the server costs 110 euros for personal and hobby usage, although a 30 day trial version is available. Currently only the Windows Client and Server are available, but they write that Linux should be available soon.
We tested the software out with an RTL-SDR V3. The client installation process was a simple wizard and after installation we launched the Cloud-SDR client by opening the shortcut “cSDRc” in the Start Menu. We found that the hardware needed to be plugged in first for the client to recognize it. The client is basic, but can already demodulate USB/LSB/CW/AM/FMN without trouble. It also has some interesting features:
Dual channel receiver: RXA and RXB are two totally independent receivers;
Geographic integration: Display on map beacons, ADS-B reported airliners, known HF broadcast stations or any geo-localized information coming from the SDRNode server;
GPS compatibility: plug a GPS receiver to your computer and track your location on the map, record signals with your position for later processing (coverage mapping etc.); display the UTC time;
Digital Terrain Elevation: See the terrain elevation around your position, or in the direction of the antenna directly on the map (requires to download the free SRTM3 files from NASA, with 90m resolution);
MP3 audio recording: record to mp3 the demodulated streams to reduce disk requirements;
Chat with other users connected to the SDRNode Group: when used as a remote client for the SDRNode streaming server, you can interact with other users with messages or station spotting;
Time-domain analysis: the MSR mode enables analysis of any sub-band and displays in real time the time domain signals of the selected spectrum portion. This sub-band can also be recorded (with geographic position if GPS is connected) and processed with provided MATLAB®.
The Cloud-SDR Client Software
Next we tested the evaluation version of the SDR-Node server software on a remote laptop with an RTL-SDR connected. Again installation was easy, just follow the wizard after ordering the evaluation version. SDR-Node installs itself as a Windows service which starts up automatically on boot. To set up the Node we followed the guide shown in the video below. To connect with the client you need to know the IP address of the remote computer, the port is 8080, and the certificate is displayed on the server PC SDR-Node dashboard. We note that we also had to disable the Windows firewall to get it to connect, but it should be possible to also add SDR-Node to the firewall whitelist.
When streaming it appears that only 1/4 of the SDR sample rate can only be sent over the network. There are also compression options which can be used on slower networks or the internet to reduce bandwidth. Using the interface while in network mode was slightly laggy, but the waterfall and audio was smooth.
Overall everything worked as expected and it looks to be a very useful tool. More information is available at cloud-sdr.com. Some already existing alternative remote SDR streaming software that supports the RTL-SDR includes rtl_tcp, the SDR Console V2 server, OpenWebRX and ShinySDR.
Many thanks to Simon Brown for updating SDR-Console V3 Preview to fully support both the RSP1 and the RSP2- you can download the software from http://sdr-radio.com/v3_preview_downloads (be sure to click on the software link under where it says ‘Downloads’ unless you want to download the software from the advertisers who support Simon’s work!)
As new YouTube demo videos of SDR-Console V3 in action become available, we will add them to the playlists on our YouTube Channel: www.youtube.com/c/SDRplayRSP
The RSP2 now supports its native SDRUno software, HDSDR through an extIO module, CubicSDR and now SDR-Console V3.
Over on our new YouTube channel we’ve uploaded a video comparing the SDRplay RSP1 and RSP2 on reception of Non-Directional Beacons at around 350 kHz. Both radios had their gains adjusted for the best possible SNR and reception. They were connected through a splitter to a Wellbrook Magnetic Loop antenna. The Hi-Z port on the RSP2 was used as Port A and Port B don’t have good reception below about 1 MHz.
In all tests the RSP2 appears to have the better SNR, a lower noise floor and thus better audio, though from the spectrum view the RSP1 seems to have a little less spurs.
Subscribe and keep an eye on our new YouTube channel as soon we’ll be uploading more RSP1 vs RSP2 comparisons, Airspy vs RSP2 comparisons and other SDR related videos as well.
DB Gain’s review first covers the features of the RSP2, and some basic SDR vs Analogue theory. He talks a bit about what criteria makes a good SDR and discusses why SDRs are so good for digital work. The review then goes on to talk about the SDRuno software, sensitivity settings, and voice mode work. The review mostly concerns the RSP2’s use on HF, and in this respect DB Gain appears appears to be extremely impressed with the results that the RSP2 gives him.
We’re happy to announce that in conjunction with Mike, one of the leaders in the SDRplay users community, we have manufactured and released a high quality aluminum enclosure upgrade for the SDRplay RSP-1 software defined radio. The SDRplay RSP-1 is a $129 USD 12 bit SDR that can tune between 10 kHz – 2 GHz. It comes by default in a simple plastic enclosure. Upgrading to a metal case enclosure not only looks sleeker, but also shields the RSP-1 from strong RF interference directly entering the PCB.
The enclosure also comes with a bonus RTL-SDR Blog broadcast FM (BCFM) filter to help reduce overloading and images from extremely strong broadcast FM stations. This filter can be installed either inside or outside the metal enclosure.
Also included is a semi-hardshell travel case which is perfect for protecting the RSP-1 while on the move. Finally, some accessories such as a thermal pad for mounting, grounding lug with nuts, 3M rubber feet and of course the enclosure screws are also included.
The cost of the enclosure including all extras is $39.95 USD with worldwide shipping included. The case is available from our Chinese warehouse for customers anywhere in the world, and in a few days it will also be able on Amazon USA for faster local US shipments. Shipping on Amazon should also be free as the free shipping threshold on Amazon was recently reduced back down to $35 USD.
Over on YouTube Jon, head of SDRplay marketing has uploaded a video showing how the SDRplay RSP2 can be used for accurate RF power measurements. In the video he shows how well calibrated the RSP2 is by comparing how well the power measurements in SDRuno match with a signal generator at various frequencies and power levels.
Later in the video he shows how RF power measurements can be used in a field situation by using the RSP2 and SDRuno to compare the performance of two different whip antennas.
A new reasonably priced 5-band HF preselector has been released by the company Cross Country Wireless, and it looks perfect for use with SDRs. The price is $56.95 GBP, which right now is about $72 USD. They write:
This can be used to provide additional front end selectivity for HF and medium wave receivers protecting the receiver from strong out of band transmissions, wideband noise and other transmitters on multi-station field days.
As the sunspot cycle declines and more listening is done on the lower HF bands with long wire antennas and strong NVIS signals then the HF Preselector is an ideal accessory to aid receiver performance.
It is invaluable when using simple conventional superhet or SDR receivers such as RTL-SDR dongles with upconverters or SDRPlay with large HF antennas.
It is an ideal tool to reduce ADC overload on the Icom IC-7300 with the new second receiver socket modification kit.
It can also be used with other transceivers that have sockets for a separate receiver input and receive antenna output.
It also covers the medium wave broadcast band for MW DXers.
The Preselector is a passive high Q design that does not use an additional amplifier or require external power.
Frequency tuning range: 0.5 to 52 MHz in five bands
Over on YouTube user SignalSearch has uploaded a video showing and explaining the use of a W4OP magnetic loop antenna on a SDRplay SDR. On the video he explains what the W4OP loop is, and demonstrates it’s operation in SDR-Console with his SDRplay. The video description reads:
Experiment: Hookup the SDRPlay RSP 1 (SDR receiver) to the W4OP (Small Transmitting Loop). I’ve always wanted to try hooking up a loop to my SDRPlay. Though different from an active receive loop (one that has a Low Noise Amplifier), this loop can be used for transmitting @ QRP levels – but works great for shortwave listening too! For more info. please visit my website @ www.k5acl.net!
Mike (kd2kog), our partner on the SDRplay RSP1 Metal case upgrade kit has recently uploaded an instruction set that shows step by step how to perform the upgrade (pdf). It shows how to dismantle the RSP1 from the plastic case, install the included broadcast FM filter, mount the PCB and shows where all the nuts and washers go.
The metal case upgrade is something we brought out back in March. It allows owners of the SDRplay RSP1 SDR to upgrade the default plastic case to a sturdy metal one for improved ruggedness and RF shielding. It also comes with an included broadcast FM filter to help reduce strong FM images which are often a problem on some bands with the RSP1. It also comes with a handy travel case. If you want to purchase the enclosure we have it available on our store at www.rtl-sdr.com/store, and also on US Amazon, both with free shipping.
Over on his blog USA-Satcom has released his XRIT (LRIT/HRIT) decoder for GOES satellites. The software requires a licence and costs $100 USD. GOES-13 (East), GOES-15 (West) and the new GOES-16 are geosynchronous orbiting satellites that broadcast very nice high resolution weather images of the entire visible disk of the earth. The transmit their LRIT/HRIT signals at about 1.7 GHz at fairly weak power, which means that a good LNA and dish set up is critical to be able to receive them. A dish size of about 1 meter, or an equivalent grid or Yagi is recommended as the lowest starting point.
GOES Full Disk Image of the Earth
USA-Satcom’s decoder is Windows based and comes with a nice GUI. Some portions of the code are based on the Open Satellite Project created by Lucas Teske. It currently supports the Airspy R2/Mini and the SDRplay RSP2 software defined radios.
The software is not free, it costs $100 USD for the licence. To help curb illegal distribution of his software which has been rampant in the past, USA-Satcom also requests that you show some proof of a working setup which is capable of receiving the GOES signal before inquiring about the software.
If you are also interested, USA-Satcom did an interesting talk at Cyberspectrum a few months ago, and he has also recently uploaded his slides.
Mike Ladd, one of the top volunteer contributors of the SDRplay community was recently hired by SDRplay officially and has now been working on a fairly comprehensive SDRuno tutorial series over on the SDRplay YouTube channel. SDRuno is the official software for the SDRplay line of SDRs and is a slightly modified version of the ‘Studio1’ software which was previously acquired by SDRplay. SDRuno also supports the RTL-SDR.
SDRuno is a complex piece of software with many features and settings, so it’s great to see a comprehensive video tutorial like this. Mike’s tutorial series currently has 10 episodes, and discusses things like the basic layout and settings of SDRuno, using Virtual Audio Cable (VAC), noise reduction, memories, calibration, DSD, notch filters and FM broadcast with RDS. More videos are probably still on the way.
LilacSat-1 is an educational CubeSat built by students from the Harbin Institute of Technology (HIT) in China. It was recently launched from the ISS on 25 May 2017 as part of the QB50 science experiment to explore the lower thermosphere, and it is expected to stay in orbit for about 3 months. Apart from BPSK telemetry at 145.935 MHz, LilacSat-1 is interesting because it contains on board an FM to Codec2-BPSK digital voice amateur radio transponder at 145/436 MHz (uplink/downlink). It is probably the first amateur radio satellite to contain an FM to digital voice transponder.
To decode LilacSat-1 digital voice and telemetry you can use a Linux live CD provided by HIT, or download the GNU Radio decoder directly from the LilacSat-1 information page on the HIT website. The GNU Radio program can be used with any GNU Radio compatible SDR, such as an RTL-SDR.
An example of LilacSat-1 being decoded has also been uploaded by YouTube by Scott Chapman. In his test he used an RTL-SDR to work the pass live, but in the video shows an offline decoding received by his SDRplay which was also monitoring the same pass.
Over on YouTube user Kevin Loughin has recently uploaded a video that shows a step by step guide on how to set up an SDRplay RSP2 in Linux. Setting up the RSP2 in Linux is not a simple task, but Kevin’s video walks us through the entire process step by step. At the end of the process you’ll be set up with the SoapySDR framework which is the glue software that sits between the hardware driver and SDR software. You’ll also have the CubicSDR software installed which is what you use for general browsing and listening. CubicSDR is similar to SDRuno, SDR#, HDSDR etc.
Over on YouTube user Kevin Loughin has uploaded a video demonstrating his SDRplay RSP2 running on a Raspberry Pi 3. The software he uses is CubicSDR which is a multiplatform program that is similar to software like SDRUno, SDR#, SDR-Console, HDSDR etc. The video shows CubicSDR running, but the interface is quite slow and laggy, although the audio is at least not choppy.
In a previous post we showed one of Kevin’s earlier videos where he does a tutorial and some scripts that help to actually set up the SDRplay drivers and CubicSDR in Linux. In the new video he first goes over a specific hack that needs to be done in Raspbian to fix the PulseAudio server. Then he explains that you can run the Linux build script mentioned in his previous tutorial video and it should work on the Raspberry Pi 3 just fine. Finally he mentions that CubicSDR and the SDRplay use a high amount of CPU processing on the pi3 so some sort of cooling mechanism is required or the pi3 may throttle down its CPU.
Over on YouTube user MaskitolSAE has uploaded a video showing him receiving some noise bursts from Jupiter with his SDRplay RSP1. The planet Jupiter is known to emit bursts of noise via natural ‘radio lasers’ powered partly by the planets interaction with the electrically conductive gases emitted by Io, one of the the planets moons. When Jupiter is high in the sky and the Earth passes through one of these radio lasers the noise bursts can be received on Earth quite easily with an appropriate antenna
In his video MaskitolSAE shows the 10 MHz of waterfall and audio from some Jupiter noise bursts received with his SDRplay RSP1 at 22119 kHz. According to the YouTube description, it appears that he is using the UTR-2 radio telescope which is a large Ukrainian radio telescope installation that consists of an array of 2040 dipoles. A professional radio telescope installation is not required to receive the Jupiter bursts (a backyard dipole tuned to ~20 MHz will work), but the professional radio telescope does get some really nice strong bursts as seen in the video.
SDRPlay have just announced that their RSP1 unit has just been reduced in price to $99.95 USD. Their press release reads:
SDRplay are pleased to announce a price reduction for their entry-level SDR receiver, the RSP1 to $99.95 USD making it the most competitive mid-range SDR to include reception down to low frequencies without the need for an upconverter. The RSP1 provides general coverage receiver and panadapter capability from 10 kHz to 2 GHz. As well as providing SDRuno SDR software, support for popular 3rd party packages like HDSDR, SDR-Console and Cubic SDR is provided. Recent availability of an SD Card image makes for easy set up on a Raspberry Pi.
Over time we’ve seen the RSP1 reduce in price originally from $299 USD, to half price at $149 USD in March 2015 and then to $129 USD in September 2016, and now finally down to $99 USD. The newer RSP2 remains at a price of $169.95 USD.
During July 24-31 the large Arecibo Radio Observatory in Puerto Rico (the big dish antenna that you may be familiar with from the movie ‘Contact’) ran an Ionospheric heating experiment which involves transmitting 600kW of net power up into the Ionosphere. This type of experiment is used for researching plasma turbulence in the ionosphere and upper atmosphere.
“The new Arecibo ionosphere HF heater nominally transmits 600 kW net power and has a unique Cassegrain dual-array antenna design that increases gain of three crossed dipoles for each band, using the signature 1000-foot spherical dish reflector,” explained Chris Fallen, KL3WX, a researcher at the University of Alaska-Fairbanks HAARP facility. He has reported that Arecibo would use 5.125 or 8.175 MHz, depending upon ionospheric conditions, but emphasized that these are estimates and frequencies may be adjusted slightly. On July 25, Arecibo was transmitting on 5.095 MHz.
Over on YouTube Mike L. used his SDRplay RSP1 together with our BCAM HPF to record some transmissions from the observatory.
Over the last few months we’ve been posting and getting excited about the Airspy HF+, an upcoming high dynamic range HF/VHF receiver designed for DXing. The Airspy team were kind enough to supply us with an early pre-production unit for review.
Long story short, the Airspy HF+ is probably one of the best low cost SDRs we’ve seen for DXing or weak signal reception out there. So far few details on the availability of the HF+ have been released, but we’re aware that preorders are due to start soon, and the target price is expected to be $149 USD from iTead Studio in China.
What follows is the full review and comparisons against other similarly priced SDRs. The Airspy team want us and readers to understand that our review unit is a pre-production model, and apparently already the matching and thus SNR has already been improved by about 2-4 dBs, so the sound samples we provide in the review below should sound even better with the newer revision.
Disclaimer: We received the HF+ for free in exchange for an honest review, but are not affiliated with Airspy. We’ve been in contact with the Airspy team who have helped clarify some points about the architecture and technology used in the design.
Introduction
The Airspy HF+ is designed to be a HF/VHF specialist receiver with a frequency range of DC to 31 MHz, and then 60 to 260 MHz. It has a maximum bandwidth of 768 kHz. So the question is then, why would you consider buying this over something like the regular Airspy R2/Mini or an SDRplay RSP2 which both have larger frequency ranges and bandwidths? You would buy the Airspy HF+ because has been designed with DXing and weak signal reception in mind. Basically the main idea behind the HF+ is to design it so that it will never overload when in the presence of really strong signals. Combined with it’s high sensitivity, weak or DX signals should come in much clearer than on the other radios especially if you have strong blocking signals like broadcast AM/FM around.
Aside: What is overloading, intermodulation and dynamic range?
Basically strong signals can cause weak signals to be drowned out, making them not receivable, even though they’re there at your antenna. This is called overloading or saturation. Intermodulation occurs when the SDR overloads and results in images of unwanted signals showing up all over the spectrum.
A simple analogy is to think about what happens when you are trying to drive, but there is sunstrike. The road is very hard to see because the sun is so bright and right in your eyes. The human eye does not have enough “dynamic range” to handle the situation of sunstrike. Dynamic range is a measure of how well a radio (eye) can handle strong (bright) and weak (dark) signals at the same time. The same analogy applies to radios which can struggle to ‘see’ weak signals if there is a very strong signal nearby on the frequency spectrum. There are a few ways to solve this:
Filtering: Block the strong signals that you don’t want using LC filters.
Eye analogy: using your sun visor to block the sun.
Attenuation: Reduce the strength of all signals.
Eye analogy: using sunglasses or squint.
Increase dynamic range: Get a better SDR with better design/technology and more bits in the ADC.
Eye analogy: upgrade your eyes.
Technology and Architecture
The HF+ uses a typical Filter->Tuner ->ADC architecture. So it is not a direct sampling receiver like most of the more expensive SDRs. Direct sampling receivers directly sample the analogue spectrum, without the need for a tuner so they avoid losses and the intermodulation problems that usually come from the mixing stages. But there are some major cutting edge technology differences in the HF+ architecture that should make its performance even better than direct sampling receivers.
Tuner: The tuner on the HF+ is one of the first to use a “Polyphase Harmonic Rejection” architecture. Essentially this means that harmonics produced in the mixing stages are naturally rejected, making the front end filtering requirements much more relaxed. So unlike the tuners used in other SDRs, this one is extremely unlikely overload in the mixing stage.
An additional benefit to this architecture is that the mixer is very low loss, so the LNA in the tuner only needs to use low gain, giving it a very high IIP3 value. So the first LNA which is typically another point of saturation and imermodulation, is very unlikely to saturate in the HF+ design. Most of the amplification only occurs after the mixing stage with the filtered narrowband output of the tuner.
Analogue to Digital Converter (ADC): The ADC is 16-bits and uses a “Sigma Delta” (ΣΔ) design. Basically a Sigma Delta ADC has a natural filtering ability due to its narrowband nature. Instead of seeing say a 30 MHz signal, it only sees 1 – 2 MHz, thus increasing dynamic range and reducing the likelihood of out of band overload.
Digital Down-Converter (DDC): Then after the ADC is a DDC which decimates the output from the ADC, increasing the effective number of bits. The more bits the larger the resolution of the digitized RF signal, so weak signals are less likely to be lost when converted from analogue to digital.
The HF+ Block Diagram
So the block diagram flow goes like this:
A weakly filtered signal enters the tuner, is weakly amplified by the tuner LNA, mixed down to baseband and filtered to 1-2 MHz. It is then amplified and sampled with the sigma delta ADC into 16-bits. The DDC decimates the output into 18-bits which is then sent to the microcontroller and PC via USB.
The Airspy team also compiled this comparison chart for us to understand the differences in architecture between the current SDRs on the market (click to enlarge). This shows that the HF+ is a different type of design compared to other SDRs. Generally the best SDRs out the market right now are direct sampling receivers with many filter banks. The HF+ approaches the problem in a different way, and according to the specs seems to match or better the performance of heavily filtered direct sampling receivers.
Performance from the Airspy HF+ product page is stated as:
-141.0 dBm (0.02 µV / 50 ohms) MDS Typ. at 500Hz bandwidth in HF
-141.5 dBm MDS Typ. at 500Hz bandwidth in FM Broadcast Band (60 – 108 MHz)
-139.5 dBm MDS Typ. at 500Hz bandwidth in VHF Aviation Band (118 – 136 MHz)
-139 dBm MDS Typ. at 500Hz bandwidth in VHF Commercial Band (136 – 174 MHz)
-138 dBm MDS Typ. at 500Hz bandwidth in the upper VHF Band (> 174 MHz)
+26 dBm IIP3 on HF at maximum gain
+13 dBm IIP3 on VHF at maximum gain
110 dB blocking dynamic range in HF
95 dB blocking dynamic range in VHF
Software and User Experience
The Airspy HF+ runs on the standard SDRSharp software. The first thing you notice when selecting the HF+ on the SDRSharp menu is how simple the controls are. There is no gain control – the AGC algorithm automatically adjusts the internal gain for maximum SNR, whilst ensuring zero overloading. The only control is the bandwidth selector where you can select from 768 kHz, 384 kHz, 192 kHz, 96 kHz and 48 kHz. Browsing the spectrum without having to adjust the gain slider is quite a liberating experience and the AGC always seemed to optimize the reception nicely.
All the controls you get/need for the HF+
The HF+ is also compatible with the SpyServer software, which allows you to stream the data radio IQ data over a network. SpyServer saves network bandwidth by sending only the currently actively tuned IQ signal plus the waterfall data. This is in contrast to other SDRs like KiwiSDR which send only compressed audio, or rtl_tcp which sends the full IQ data. Sending the IQ data rather than compressed audio allows you to perform various DSP algorithms to the signal on the host side, such as noise filtering. Sending the IQ data (even if only a slice of it) still uses significantly more bandwidth compared to sending compressed audio however, so internet connections and wideband signals such as BCFM may not work well together over long distances and slow internet connections.
External Design/Photos
Note that our pre-production unit does not have the completed metal finish to it yet. The final version is supposed to have a more aesthetically pleasing metal finish applied to the enclosure.
The HF+ is about the size of a pack of cards, and comes in a 90 x 55 x 3 mm metal enclosure with the Airspy HF+ logo stamped onto the top. This thick enclosure gives the HF+ quite some weight at 190 g and a very sturdy feel to it. There are two SMA ports on the left for HF and VHF antennas, and a USB micro port on the right. Two small status LEDs are placed near the SMA ports.
Inside is the PCB, and the main RF circuitry is shielded with a metal can (ignore the poor soldering on the can as this was removed and replaced by us when performing a small mod to the pre-production unit). This double shielding means that the HF+ is well protected against stray RF and USB noise. Also, one interesting feature is the use of a grounding spring on the bottom plate which ensures that the USB connector is grounded with a low impedance connection to the metal enclosure.
Comparison SDRs
In this review we are doing side by side comparisons of the HF+ against similarly priced SDRs, including the ColibriNANO, Airspy Mini + SpyVerter Upconverter and the SDRplay RSP2.
In these tests we compare each SDR on a real world signal. SDRs are cycled through, taking screenshots and recording audio as fast as possible to ensure that conditions don’t change. To verify conditions didn’t change part way through we go through our loop twice to confirm that similar results are recorded.
The HF and below tests use a Wellbrook Loop antenna. VHF Tests use a discone or dipole tuned for the tested band. The RF environment is one with strong broadcast AM and FM stations. The location is 10km away from an AM tower, and LOS to the FM/TV transmitter tower.
In all cases the signal of interest is optimized for best SNR without overloading the SDR. For each SDR we used the officially recommended software package. For the Airspy devices this was SDRSharp, for the ColibriNANO this was ExpertSDR and for the RSP2 this was SDRUno.
With the RSP2 we used the recommended HiZ port for all LF – HF signals and also flipped between then Zero and Low-IF mode choosing the best one. Just to be sure, we tested the A and B ports on the RSP2 as well, but experienced heavy broadcast AM overload (with the filters turned off) and weaker signals than with the HiZ port with the filters on, so did not continue to use these ports.
On the ColibriNANO we used bandwidths at or below 768 kHz to get the 24-bit output.
A modern 2016 Core-i7 laptop run on battery power is used for all tests, but all SDRs were confirmed to run smoothly on an older model Core-i5 desktop PC.
LF (Low Frequency 40 kHz Time Signal)
Airspy HF+
ColibriNANO
Airspy Mini + SV
SDRplay RSP2
RTL-SDR + SV
This signal is a 40 kHz time signal originating from Japan. It is know as the Ohtakadoya-yama LF Standard Time and Frequency Transmission Station (NICT).
From the screenshots we can see that the only SDRs successful at receiving this station where the HF+ and the Airspy Mini + SV.
The HF+ comes in with a very clear copy and there is no sign of overloading from broadcast AM. VLF signals down to 20 kHz are also visible and copyable.
The Mini + SV receives the signal too, but there is significant overloading from broadcast AM stations present all around the signal.
The ColibriNANO cannot receive the signal at all. According to the advertised specifications the ColibriNANO starts receiving at around 100 kHz so this is expected. From the screenshot we start to see a response at around 70 kHz.
The RSP2 just barely receives the signal (a very faint line is visible in the waterfall), but no audio was copyable. There is some minor signs of overload from broadcast AM as well.
NDB’s (~325 kHz)
NDB’s or Non-Directional Beacons are beacons used to aide with aircraft navigation. In this test all SDRs were able to receive NDBs with good performance and it was difficult to notice a difference between SDRs.
Airspy HF+
Airspy Mini + SV
ColibriNANO
SDRplay RSP2
The HF+
The Mini + SV
The ColibriNANO
The RSP2
Broadcast AM
Here we tuned to the broadcast AM band and tested reception with one of the weaker signals.
Airspy HF+
ColibriNANO
SDRplay RSP2
The HF+ receives this weak station clearly and fading is minor.
The ColibriNANO received the station but seemed to be a bit noisier with more static coming through.
The RSP2 also receives the station clearly, but there is a bit more static noticeable in the background.
2.6 MHz FAX
Receiving a fax signal about 1 MHz above the broadcast AM band.
Airspy HF+
ColibriNANO
SDRplay RSP2
The HF+ received the fax cleanly.
The Mini + SV was not tested as the fax finished before we could get to it.
The ColibriNANO received the fax cleanly.
The RSP2 received the fax as well as the other receivers, but on the waterfall are some broadcast AM station images. Reducing the gain reduced the fax signal strength, but the images remained as well.
7 MHz Shortwave
Airspy HF+
Airspy Mini + SV
ColibriNANO
SDRplay RSP2
The HF+ receives weak shortwave stations well with pretty clear audio.
The Mini + SV has similar performance to the HF+
The ColibriNANO seems to be a bit noisier.
The RSP2 experienced quite a bit of fading which wasn’t as intense on the other SDRs. It didn’t seem to be related to changing conditions as switching back to another SDR after the RSP2 didn’t show the effect.
96.03 MHz FM
This is a low power DX station, very closely spaced to a powerful station on the frequency spectrum.
Airspy HF+
Airspy Mini + SV
ColibriNANO
SDRplay RSP2
The HF+ quite clearly has a very noticeable sensitivity edge on the broadcast FM spectrum as can be heard in the audio examples. The HF+ audio seems to be noticeably clearer.
The AS Mini receives the station too, but it noticeably noisier.
The ColibriNANO cannot receive the station at all. As it is working in undersampling mode, it is possibly overloaded. To use undersampling mode successfully filters are required.
The RSP2 works similarly to the AS Mini.
96.2 MHz FM
Receiving a regular non-E’s FM station about 120km away.
Airspy HF+
Airspy Mini
SDRplay RSP2
ColibriNANO
The HF+ was able to receive the FM station fairly clearly
The AS Mini could also receive the station, but the audio was barely audible. Turning up the gain further caused overload, a rise in the noise floor and a weakening of the SNR.
The ColibriNANO could not receive this station, so we did not record any audio.
The RSP2 was also able to receive the station, but like the AS Mini the audio was barely audible.
Pagers
In this location we have some very strong pagers at 158 MHz and most SDRs show signs of overloading near to the pager frequency. The HF+ seemed to handle them quite well, however when two transmitted at once there was a about a 100ms period of overload before the AGC kicked in to reduce the gain.
HF+ Receiving strong pagers. Two transmitting at once.
Here we tested a weak signal about 2.5 MHz below the pagers.
Airspy HF+
Airspy Mini
SDRplay RSP2
The HF+ was able to clearly receive this data station without any sign of overload from the pagers.
The Airspy Mini could also receive the station, but much weaker. Turning up the gain any further caused overload, and caused pager + WFM noise to appear over the frequency whenever the pager transmitted. Even at a gain setting of 10 there was some mild interference noticeable in the screenshot when the pager transmitted.
The RSP2 could also receive the station with fairly good strength, but intermodulation was severe whenever the pager transmitted, causing a loss of signal. Turning down the gain did not help with the interference, and only reduced the signal of interests’ strength further. Enabling the MW/FM filter did not help as the pager interferer is outside the notch range.
The ColibriNANO could not receive this station.
Conclusions
The Airspy HF+ is an exceptional SDR and will truly please any DXers or people wishing to listen to weak stations. It is a relatively narrowband SDR (in comparison to say the Mini/R2 and RSP2) that can only tune up to 260 MHz, so don’t expect to be able to use it as a wideband scanner for trunked radios for example. But on VHF it would perform very well on FM DX, airband voice scanning and for 137 MHz WX satellites. The reception on the HF+ is almost entirely unaffected by extremely strong pagers in the 157 MHz region.
Below 30 MHz the HF+ also shines. VLF to MW is the best we’ve seen on any sub $300 SDR. Overload is non-existent on broadcast AM, and no effects from the strong AM signals can be seen further up on the spectrum.
The closest competing unit to the HF+ in terms of price and use cases (designed for HF) is probably the ColibriNANO. But the ColibriNANO commands a decently higher price at $350 USD. Performance on HF seems similar, but we do have to give a slight edge to the HF+. The ColibriNANO also has the downside of poor LF/VLF reception (advertised response starts at 100 kHz), and heavily aliased VHF/UHF due to undersampling. A filter is needed for proper operation on VHF/UHF. That said the ColibriNANO itself is a very good SDR, but the HF+ certainly wins out in terms of value and general performance and we can’t see any situation where the ColibriNANO would be a better choice at the moment.
The Airspy Mini/R2 and SDRplay RSP2 also generally perform well for the majority of signals, but will struggle when it comes to really strong signals. Comparing against these SDRs on weak signals near strong blockers really shows where the HF+ shines. But when compared against regular (non-weak) signals or in a tame RF environment without strong signals then it is pretty much impossible to determine which SDR is better.
So there is obviously some brand new cutting edge technology going on in this receiver with the polyphase harmonic rejection mixer and the sigma delta ADC which possibly even puts it on top of the very expensive direct sampling SDRs. On the HF+ weak and DX signals are noticeably more accessible. Performance for the price (expected $149USD) is phenomenal. This is a highly recommended SDR.
Disclaimer: We received the HF+ for free in exchange for an honest review, but are not affiliated with Airspy. We’ve been in contact with the Airspy team who have helped clarify some points about the architecture and technology used in the design.
LilacSat-1 is an educational CubeSat built by students from the Harbin Institute of Technology (HIT) in China. It was recently launched from the ISS on 25 May 2017 as part of the QB50 science experiment to explore the lower thermosphere, and it is expected to stay in orbit for about 3 months. Apart from BPSK telemetry at 145.935 MHz, LilacSat-1 is interesting because it contains on board an FM to Codec2-BPSK digital voice amateur radio transponder at 145/436 MHz (uplink/downlink). It is probably the first amateur radio satellite to contain an FM to digital voice transponder.
To decode LilacSat-1 digital voice and telemetry you can use a Linux live CD provided by HIT, or download the GNU Radio decoder directly from the LilacSat-1 information page on the HIT website. The GNU Radio program can be used with any GNU Radio compatible SDR, such as an RTL-SDR.
An example of LilacSat-1 being decoded has also been uploaded by YouTube by Scott Chapman. In his test he used an RTL-SDR to work the pass live, but in the video shows an offline decoding received by his SDRplay which was also monitoring the same pass.
