Alexander Csete (OZ9AEC) is the programmer behind the popular GQRX software. Recently Alexander has received a review sample of the upcoming Airspy HF+ and has been uploading videos showing it in action to his YouTube channel.
The Airspy HF+ is a soon to be released low cost (expected price $149 USD) yet high performance HF/VHF receiver designed for DXing with exceptional performance in the presence of strong overloading signals. If you are interested we also have our own review of the HF+ available here.
In the video below Alexander demonstrates the HF+ on SSB and CW modes in his GQRX software. See his YouTube channel for the rest of the videos. Currently there are about 7 videos demonstrating the HF+ on his channel.
Over on his Twitter account @csete Alex has also been uploading several images of the HF+ in action as well as some screenshots of it being compared against the RFSpace Cloud-IQ which is a $629 USD SDR. So far his impressions of the HF+ seem very high.
Testing the Airspy HF+ with Gqrx, then a pirate comes by...
Looks like the radar guys have learned to stay outside the amateur radio bands. Now we can study selective fading ? pic.twitter.com/8y8rDoXJh0
Side by side comparison of Cloud-IQ and Airspy HF+ on MW
Cloud-IQ: 370120 sps (RBW 22.6 Hz)
Airspy HF+: 768000 sps ↓2 (RBW 23.4 Hz) pic.twitter.com/uUUard2XmZ
The Airspy HF+ on the other hand is based on a polyphase harmonic rejection mixer design with 18-bit DDC and has a frequency range of DC – 31 MHz and 60 – 260 MHz, with a maximum bandwidth of up to 660 kHZ. It is not yet released, but is expected to be about US $149 shipped from China.
Simon’s screenshots show that despite its low cost the HF+ seems to perform just as well as the more expensive NetSDR.
By connecting the output of the noise source to the SWR-bridge input, and the antenna to the DUT port the return loss or SWR of the antenna can be measured with the Airspy. To get a wider than 10 MHz view of the spectrum Anders uses the SpectrumSpy software for the Airspy which is a spectrum analyzer application that allows you to view any bandwidth that you like. With the Airspy, noise source and antenna all connected correct to the SWR-Bridge significantly notches in the spectrum show up in SpectrumSpy. These notches are the resonant points of the antenna. Visually seeing these notches allows you to fine tune the length of the antenna elements for best SWR.
How to connect it all upSpectrumSpy showing the resonant notches at 40m and 20m.
Over on Twitter @lambdaprog and @mm6dos, developers of SDR# and Airspy SDR products have tweeted videos showing off an Android watch being used as an SDR interface. They use a prototype of their upcoming Airspy HF+ SDR, their SpyServer streaming software and an Android watch. The Android watch receives the streaming FFT and audio data from a server running the SpyServer and Airspy HF+.
They write that this new SpyServer client is mainly for phones and tablets and is efficient enough to run on a watch. It appears that this lightweight version of the SpyServer sends compressed FFT and audio instead of a slice of the IQ data like the current SpyServer, making it very light on the client side CPU and network usage.
If you’re interested in the Airspy HF+ we have an initial review available here.
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)
The Airspy HF+ is an upcoming product from the Airspy team that is intended to be a high performance HF/VHF receiver at a low price. Its frequency range will be DC to 31 MHz, and 60 to 260 MHz and the bandwidth will be about 660 kHz. So why choose the HF+ over the Airspy R2, Mini or SDRplay which all have larger frequency ranges and bandwidths? It seems the focus of the HF+ is to be an extremely high dynamic range receiver. This means that strong signals should almost never overload the receiver making it very good for DXing weak signals (listening to weak signals from very far away). On other receivers once you turn the gain up strong signals can block reception of the weaker ones.
Recently we saw the release of some of the first 3D renderings of the product. Now finally we have a photo of the actual PCB which is shown below. The RF sensitive innards are hidden away within a shielding can, but we know from the product page that inside are the switches, filters, tuner, ADC and 18-bit DDC.
The Airspy HF+ PCB
Also, over on Twitter, @lambdaprog, lead creator of SDR# and of the Airspy HF+ has uploaded some sensitivity tests. It seems that sensitivity will be at least -136 dBM at 20 meters, as a -136 dBm signal still comes in with 21 dB of SNR. Similar sensitivity results are obtained on the FM Band.
Sensitivity tests of the prod revision of the Airspy HF+. It looks like -136 dBm still gives a good readable signal on 20m. cc @ITeadstudiopic.twitter.com/n4KaKi0eAB
The Airspy team have sent us a sample unit from an early manufacturing test and we hope to have a full review available a few weeks after we receive it.
SDR-Console is a popular RTL-SDR compatible multi purpose SDR software package which is similar to programs like SDR#, HDSDR and SDRuno. Currently SDR-Console V2 is the stable version and SDR-Console V3 is in a beta state. A few days ago SDR-Console V3 Preview 6 was released. It comes with some very interesting new features including a built in Airspy server, a recording scheduler, a new feature called signal history and a new receivers pane.
“Signal History” takes the signal strength of the given bandwidth each 50 milliseconds, which can be saved in a CSV file. It is also shown in three different speeds on a display.
“Receivers’ Pane” shows up to six combos of spectrum/spectrogram of the complete up to 24 parallel demodulators (they additionally can be shown in the Matrix, as in former versions).
“Signal History” offers many applications, to name just three:
analyze fading and its structure with an unsurpassed time resolution of 50 ms
document fade-in and fade out
measure signal-to-noise ratio of signals
In addition Nils has also uploaded a very useful 19 page PDF where he writes step by step instructions and shows numerous examples of the new signal history tool.
DK8OK’s SDR-Console V3 P6 Screenshot. Showing multiple receiver panes and the new signal history feature.DK8OK’s screenshot of the signal history toolbox.
Back in February of this year we first heard about the Airspy HF+, which is an upcoming product from the Airspy team that is intended to be a high performance HF receiver at a low price. Over on the Airspy HF+ website the first (rendered) image of the unit has recently been released. We’ve also managed to get some additional renderings from the Airspy team which we show in the image slider below.
The enclosure is CNC carved aluminum with two SMA ports on one side, and a USB port on the rear. Since the HF+ actually has the capability to tune up to 260 MHz it uses two SMA inputs, one for an HF antenna and one for a VHF antenna. Inside the RF circuit is shielded again with a shielding can to protect it from USB noise.
The tweet below also appears to show some grounding improvements made to reduce USB noise.
The Airspy HF+ is also the result of a long learning journey and a great attention to details. USB noise is past! cc @ITeadstudiopic.twitter.com/6RJykinRWq
Other recent tweets from prog (the creator of the Airspy HF+) indicate that the hardware is ready, and show that streaming from with SpyServer from a RPi3 is functional. Hopefully we should be seeing this unit release for sale soon.
Alexander Csete (OZ9AEC) is the programmer behind the popular GQRX software. Recently Alexander has received a review sample of the upcoming Airspy HF+ and has been uploading videos showing it in action to his YouTube channel.
The Airspy HF+ is a soon to be released low cost (expected price $149 USD) yet high performance HF/VHF receiver designed for DXing with exceptional performance in the presence of strong overloading signals. If you are interested we also have our own review of the HF+ available here.
In the video below Alexander demonstrates the HF+ on SSB and CW modes in his GQRX software. See his YouTube channel for the rest of the videos. Currently there are about 7 videos demonstrating the HF+ on his channel.
Over on his Twitter account @csete Alex has also been uploading several images of the HF+ in action as well as some screenshots of it being compared against the RFSpace Cloud-IQ which is a $629 USD SDR. So far his impressions of the HF+ seem very high.
Testing the Airspy HF+ with Gqrx, then a pirate comes by...
Looks like the radar guys have learned to stay outside the amateur radio bands. Now we can study selective fading ? pic.twitter.com/8y8rDoXJh0
Side by side comparison of Cloud-IQ and Airspy HF+ on MW
Cloud-IQ: 370120 sps (RBW 22.6 Hz)
Airspy HF+: 768000 sps ↓2 (RBW 23.4 Hz) pic.twitter.com/uUUard2XmZ
The Airspy HF+ on the other hand is based on a polyphase harmonic rejection mixer design with 18-bit DDC and has a frequency range of DC – 31 MHz and 60 – 260 MHz, with a maximum bandwidth of up to 660 kHZ. It is not yet released, but is expected to be about US $149 shipped from China.
Simon’s screenshots show that despite its low cost the HF+ seems to perform just as well as the more expensive NetSDR.
By connecting the output of the noise source to the SWR-bridge input, and the antenna to the DUT port the return loss or SWR of the antenna can be measured with the Airspy. To get a wider than 10 MHz view of the spectrum Anders uses the SpectrumSpy software for the Airspy which is a spectrum analyzer application that allows you to view any bandwidth that you like. With the Airspy, noise source and antenna all connected correct to the SWR-Bridge significantly notches in the spectrum show up in SpectrumSpy. These notches are the resonant points of the antenna. Visually seeing these notches allows you to fine tune the length of the antenna elements for best SWR.
How to connect it all upSpectrumSpy showing the resonant notches at 40m and 20m.
Over on Twitter @lambdaprog and @mm6dos, developers of SDR# and Airspy SDR products have tweeted videos showing off an Android watch being used as an SDR interface. They use a prototype of their upcoming Airspy HF+ SDR, their SpyServer streaming software and an Android watch. The Android watch receives the streaming FFT and audio data from a server running the SpyServer and Airspy HF+.
They write that this new SpyServer client is mainly for phones and tablets and is efficient enough to run on a watch. It appears that this lightweight version of the SpyServer sends compressed FFT and audio instead of a slice of the IQ data like the current SpyServer, making it very light on the client side CPU and network usage.
If you’re interested in the Airspy HF+ we have an initial review available here.
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)
The Airspy HF+ is an upcoming product from the Airspy team that is intended to be a high performance HF/VHF receiver at a low price. Its frequency range will be DC to 31 MHz, and 60 to 260 MHz and the bandwidth will be about 660 kHz. So why choose the HF+ over the Airspy R2, Mini or SDRplay which all have larger frequency ranges and bandwidths? It seems the focus of the HF+ is to be an extremely high dynamic range receiver. This means that strong signals should almost never overload the receiver making it very good for DXing weak signals (listening to weak signals from very far away). On other receivers once you turn the gain up strong signals can block reception of the weaker ones.
Recently we saw the release of some of the first 3D renderings of the product. Now finally we have a photo of the actual PCB which is shown below. The RF sensitive innards are hidden away within a shielding can, but we know from the product page that inside are the switches, filters, tuner, ADC and 18-bit DDC.
The Airspy HF+ PCB
Also, over on Twitter, @lambdaprog, lead creator of SDR# and of the Airspy HF+ has uploaded some sensitivity tests. It seems that sensitivity will be at least -136 dBM at 20 meters, as a -136 dBm signal still comes in with 21 dB of SNR. Similar sensitivity results are obtained on the FM Band.
Sensitivity tests of the prod revision of the Airspy HF+. It looks like -136 dBm still gives a good readable signal on 20m. cc @ITeadstudiopic.twitter.com/n4KaKi0eAB
The Airspy team have sent us a sample unit from an early manufacturing test and we hope to have a full review available a few weeks after we receive it.
SDR-Console is a popular RTL-SDR compatible multi purpose SDR software package which is similar to programs like SDR#, HDSDR and SDRuno. Currently SDR-Console V2 is the stable version and SDR-Console V3 is in a beta state. A few days ago SDR-Console V3 Preview 6 was released. It comes with some very interesting new features including a built in Airspy server, a recording scheduler, a new feature called signal history and a new receivers pane.
“Signal History” takes the signal strength of the given bandwidth each 50 milliseconds, which can be saved in a CSV file. It is also shown in three different speeds on a display.
“Receivers’ Pane” shows up to six combos of spectrum/spectrogram of the complete up to 24 parallel demodulators (they additionally can be shown in the Matrix, as in former versions).
“Signal History” offers many applications, to name just three:
analyze fading and its structure with an unsurpassed time resolution of 50 ms
document fade-in and fade out
measure signal-to-noise ratio of signals
In addition Nils has also uploaded a very useful 19 page PDF where he writes step by step instructions and shows numerous examples of the new signal history tool.
DK8OK’s SDR-Console V3 P6 Screenshot. Showing multiple receiver panes and the new signal history feature.DK8OK’s screenshot of the signal history toolbox.
Back in February of this year we first heard about the Airspy HF+, which is an upcoming product from the Airspy team that is intended to be a high performance HF receiver at a low price. Over on the Airspy HF+ website the first (rendered) image of the unit has recently been released. We’ve also managed to get some additional renderings from the Airspy team which we show in the image slider below.
The enclosure is CNC carved aluminum with two SMA ports on one side, and a USB port on the rear. Since the HF+ actually has the capability to tune up to 260 MHz it uses two SMA inputs, one for an HF antenna and one for a VHF antenna. Inside the RF circuit is shielded again with a shielding can to protect it from USB noise.
The tweet below also appears to show some grounding improvements made to reduce USB noise.
The Airspy HF+ is also the result of a long learning journey and a great attention to details. USB noise is past! cc @ITeadstudiopic.twitter.com/6RJykinRWq
Other recent tweets from prog (the creator of the Airspy HF+) indicate that the hardware is ready, and show that streaming from with SpyServer from a RPi3 is functional. Hopefully we should be seeing this unit release for sale soon.
